Adrian! posted:I guess it makes sense if you don't have the TVS inside the TIU it won't fail to short. That does mean the ACT244s are taking the voltage then. They have ESD clamps on-die so they aren't completely defenseless.
I don't have a schematic of the TIU. Exactly how are the failing TVS units connected with respect to the ACT244? Are they directly from OUT to GND?
PLCProf posted:Adrian! posted:I guess it makes sense if you don't have the TVS inside the TIU it won't fail to short. That does mean the ACT244s are taking the voltage then. They have ESD clamps on-die so they aren't completely defenseless.
I don't have a schematic of the TIU. Exactly how are the failing TVS units connected with respect to the ACT244? Are they directly from OUT to GND?
Yup it’s a +\- 9.2V clamp across the output.
Adrian! posted:PLCProf posted:Adrian! posted:I guess it makes sense if you don't have the TVS inside the TIU it won't fail to short. That does mean the ACT244s are taking the voltage then. They have ESD clamps on-die so they aren't completely defenseless.
I don't have a schematic of the TIU. Exactly how are the failing TVS units connected with respect to the ACT244? Are they directly from OUT to GND?
Yup it’s a +\- 9.2V clamp across the output.
OK - Here is my scenario. This is pure semi-uneducated speculation.
The ACT244 spec calls for the output voltage to go above VCC or below GND by no more than 1/2 volt, probably to protect the ESD diodes from being pushed into conduction A TVS from the output to ground will do nothing to stop negative-going transients from pulling the output below ground, not until you are way past the 1/2 volt spec, anyway.. Those diodes may well be the failure mode of the ACT244 when subject to transient voltages on its output.
I would expect that MTH was experiencing ACT244 failures and applied the TVS as a shotgun. Apparently, the TVS is about as tender as the ACT244, but the failure effects are more noticeable. But, it doesn't really protect in all cases.
Was thinking about a couple external diodes to supplement (protect) the clamp diodes in the ACT244, then put a bigger, slower TVS (or a an appropriate zener!) from VCC to ground along with a cap (which is probably already present.) That approach would let you dissipate the transient energy somewhere other than in the signal path. It also puts the capacitance of the TVS in series with the small capacitance of a small diode, making it much less of an issue unless the diodes are conducting.
Or so it seems to me.
Interesting idea, perhaps a Schottky diode from ground and VCC to the outputs to prevent any excursion that would damage the 244 internally. That should be low enough in capacitance to not cause the issue that the TVS may cause regarding the signal and excessive capacitance. The TVS across VCC would supply added protection, and capacitance of the TVS isn't an issue when connected across VCC.
There must be a reasonable solution that will keep the chips or the protection from self-destructing in normal operation.
If you could do a 3 component solution, we might still be able to mount it right on top of the 244.
Norton posted:RJR posted:I agree with you, GRJ, on your evaluation of the PH180 breakers. I wish that some talented soul would design and sell a DIY kit to assemble such breakers, to use on train layouts. [HINT
HINT]
A few already have. The Lionel TMCC Lock on is every bit as fast and unlike the 180w brick, is self restting. Also you have DCC specialties PSX-AC. Even better as the current trip point is setable up to 15 amps and it can be used in conventional mode. No need to reinvent the wheel.
Pete
I can verify, at least in my testing, that the TMCC Direct Lockon kills the DCS signal! I tried three of them, all of them killed the signal from my Rev. L TIU. Perfect without the lockon, couldn't find engines with it.
We had the same issue with the TMCC Direct Lockon at our club. Removed them and that problem was resolved.
There may be more than one version of the TMCC Direct Lockon, but I can assure you that at least one version of it will kill the DCS signal.
Barry Broskowitz posted:Pete,
The Lionel TMCC Lock on is every bit as fast and unlike the 180w brick, is self restting. Also you have DCC specialties PSX-AC.
I'd heard (but not verified) that there were issues with signal degradation when using either one of these devices with DCS. Could you provide any insight in that regard?
Thanks!
I have PSX-ACs between the PH-180 bricks and my early Rev L TIU and have had no problems with DCS at all in the last 4-5 years or so. That was when I installed my current layout. Probably a lot of overkill, but it works for me. I like to feel safe and so far no problems.
I believe any problem comes from placing the PSX-ACs after the TIU. I think that is when you need to add the choke to eliminate the interference. PSX-ACs are a bit pricey, but a whole lot less than replacing circuit boards in your command control engines. Having to replace the boards in just one engine will buy you several PSCX-ACs.
Edit: After replying to this I read all the following posts after yours and saw that Adrian! said the same thing as I posted above about the PSX-AC. I will defer to his findings from now on.
Adrian! posted:PLCProf posted:I don't have a schematic of the TIU. Exactly how are the failing TVS units connected with respect to the ACT244? Are they directly from OUT to GND?
Yup it’s a +\- 9.2V clamp across the output.
Are you sure about this? I've asked this question before - about where EXACTLY the TVS is located. In this post from a related thread, you say:
Given this case I measured the ACT244s deferentially also to make sure there wasn't something the single ended monitoring wasn't capturing. Again in differential mode both the weak and good channels have about the same voltage swing. If you zoom into the individual bits inside both look like clean square waves.
This suggests to me that the 9.2V TVS is NOT placed across the ACT244 output. That is, if the TVS is failing (shorting) over time, how can the good and bad channels have identical signals right at the ACT244 outputs?
In any case it seems to me that Adrian! has a solution. 1N4148 diodes are a wallet-busting 1 cent a piece! So even with cost of the bare circuit board, we're talking about $1-2 (or so) per channel out-of-pocket cost. Yes, there is the tedious matter of soldering diodes and such which can be a show-stopper for some guys.
It seems to me that the idea of clamping the ACT244 output pins right at the chip itself is another candidate solution. Perhaps this solution might have fewer components and hence a smaller circuit-board and perhaps less soldering and assembly. But I can't imagine the out-of-pocket cost being much lower than $1. And this requires evaluation, testing, etc. Nothing is so easy as the job you imagine someone else doing.
I just tossed something together with a pair of Schottky diodes to limit the output excursion above and below VCC and ground, and a 1500W TVS across the outputs. I'm trying to see if it can be small enough to just stick to the top of the 244 and just wire it. Obviously, I'd probably change how it connects, this is just a sizing exercise for the components right now. These three components and the three required connections are on a board that is .675" x .2", so it's certainly small enough. The the paralleled output pins of the 244 are connected to pin 1, and the VCC and ground are connected to pins 2 & 3. I used a 1500W TVS, it's the size used for the TIU outputs, so it should be fairly robust.
The diodes are rated at 500ma with a peak surge of 14A, and their junction capacitance is fairly low, CT is 15pf. The capacitance of the TVS shouldn't matter in this configuration, one of the issues we had with the other schemes.
From Adrian! other post,
The voltage swing looks pretty much the same in both the good and bad channels so I feel it's safe to say the ACT244s are working fine. From my understanding of the traces on the PCB it looks like they the 4 left channels together to form a positive output and the 4 right channels together to form a negative output, then use it differential to drive the output transformer after a filtering network.
In other words of the 8 outputs per ACT244 chip, 4 are tied together to form "output+" and other 4 are tied together to form "output-." Hence two clamps per ACT244. I'd think you'd want to put both clamps on one board with 4 connections to the ACT244: VCC, GND, output+, output-. Just a suggestion.
Good point Stan! 
We could just add two diodes, no need for a second TVS I would imagine.
Let's see if this is closer... The four pads are to solder jumpers to the chip that we perched this on. The board dimensions are 16.5mm x 6mm, the E2 and E3 pads are spaced to connect to GND and VCC, the others two connect to the two output banks.
I guess interest in a generic solution waned a bit. I'll park this until I have a problem with one of my TIU's.
gunrunnerjohn posted:I guess interest in a generic solution waned a bit.
Yeah, I guess so.
I don't have a TIU so I can't really do any testing or analysis.
GRJ,
Interest is there, not being a tech guru, I await a solution which works, we go through TIU's like underwear and a solution would be quite welcome.
Ron
I was curious if Adrian or Stan were going to weigh in and give me their thoughts on this approach. Until I get a layout built, I can't really do any serious testing either. I suspect also, I won't have the issues that a large club layout would have with the TIU's.
gunrunnerjohn posted:I was curious if Adrian or Stan were going to weigh in and give me their thoughts on this approach. Until I get a layout built, I can't really do any serious testing either. I suspect also, I won't have the issues that a large club layout would have with the TIU's.
I like what you drew up. I don't see any reason it wouldn't work (testing is always best of course).
Any thoughts on a simple signal level monitor as oppose to a costy oscilloscope? I've got 2 or 3 ideas but they're all mixed-signal/digital ways so far (which are still expensive)
I wanted to see if anyone had any issues with what's there before trying to make a couple. I think it would be a lot easier to use than the zillions of diodes you originally used, the question is how effective would it be in protecting the TIU 244's. That can only be determined by testing in an environment that destroys TIU's. Wait... You have such an environment! 
If I share this project on OSH Park, would you be interested in putting a couple together and seeing if they survive your club torture tests? A preview shows that the board cost is 80 cents for three of them, shipped free. Of course, you do need a couple bucks worth of components.
The smallest dimension they'll do is .25", so I had to enlarge it slightly.
Here's the OSH Park Link to the shared design: MTH TIU Signal Protection
What makes me nervous about the proposed alternative is that the original 1N4148 method was apparently developed in coordination with MTH themselves (?). As I've suggested earlier, I don't believe the MTH clamp is directly on the ACT244 output based on tests Adrian! made months ago. What's my point? While it's been stated that the clamp protects the ACT244, does anyone know with certainty that the clamp doesn't protect OTHER components too? When Adrian! made the oscilloscope tests in the other post, I recall there were other semiconductor components AFTER the ACT244 in the filter circuit.
But if someone is willing to do the assembly and testing of the direct-on-the-ACT244 method then by all means fire up the soldering iron! I'd also think that one would always want to install clamps on all 4 channels so perhaps the circuit board should have 4 clamps which might save wiring (since VCC and GND) could be shared.
Even if remaining with the 1N4148 approach, I'm pretty certain you could cut the PCB board size in half using tighter bends on the leads and it looks to me like the hole sizes are larger than they need be. You could probably use the SMD LL4148 leadless version which would save space and assembly time and those are also a penny a piece. And as above I'd think you'd want to put 4 clamps on one board.
stan2004 posted:What makes me nervous about the proposed alternative is that the original 1N4148 method was apparently developed in coordination with MTH themselves (?). As I've suggested earlier, I don't believe the MTH clamp is directly on the ACT244 output based on tests Adrian! made months ago. What's my point? While it's been stated that the clamp protects the ACT244, does anyone know with certainty that the clamp doesn't protect OTHER components too? When Adrian! made the oscilloscope tests in the other post, I recall there were other semiconductor components AFTER the ACT244 in the filter circuit.
But if someone is willing to do the assembly and testing of the direct-on-the-ACT244 method then by all means fire up the soldering iron! I'd also think that one would always want to install clamps on all 4 channels so perhaps the circuit board should have 4 clamps which might save wiring (since VCC and GND) could be shared.
Even if remaining with the 1N4148 approach, I'm pretty certain you could cut the PCB board size in half using tighter bends on the leads and it looks to me like the hole sizes are larger than they need be. You could probably use the SMD LL4148 leadless version which would save space and assembly time and those are also a penny a piece. And as above I'd think you'd want to put 4 clamps on one board.
Yeah there's some discrete FETs in the output network. I haven't seen them fail, even when the diodes are short (although.... maybe that's *because* the TVS diodes are short and sacrificially protecting them ). I don't have the full network schematic, just a lot of slow (yes or no) question sessions. If anyone is willing to put time into a test PCB, I'm willing to install it in a TIU and test it in our battle arena.
My prototype wasn't meant for any kind of production or minimum cost answer, it was me coming up with a quick solution and testing it empirically over and over to make sure its functional. The idea of posting the details was to start a discussion (check that off) and to get the clever folks like GRJ to refine it.
Also just to throw this out there based on some of the comments above. I don't want to give anyone the wrong idea... not *every* DCS problem you have is because the TVS diodes failed in your TIU. If you're rough on trains, and have a later Rev L TIU, you may have this problem too, but outside of that, lots of other things can also go wrong!
Adrian, Granted other issues arise, but blowing 1-2 channels on a TIU adds up for our club, we are running 5 on the layout and have 15 we rotate as send off for repairs, if this fixes the blown channels, we are one step ahead in making the layout less maintenance intensive and our crew can make new additions vice only keeping the old running.
Shorts from derailments are a daily problem, not all members are lucky with their trains , whether inattention or a switch being thrown by someone not watching , a bad coupler opening and train meets the tail end or doesn't like a turnout. It is impossible to foolproof a layout, but removing one problem sure feels good.
Adrian! posted:Any thoughts on a simple signal level monitor as oppose to a costy oscilloscope? I've got 2 or 3 ideas but they're all mixed-signal/digital ways so far (which are still expensive)
As you pointed out earlier, it can be challenge to design a low-cost DCS signal level meter given the short, high-frequency bursts. To that end I'd think you could put a suspect DCS-channel into the Proto-cast mode where it sends hundreds or thousands of times more DCS packets than normal DCS use. My thinking is this might make it as simple as a high-pass filter (to reject the 60 Hz), and a simple averaging diode detector which could feed any DC voltmeter. Yes, this would not provide "in-service" monitoring in that you would have to stop playing with trains and put on a diagnostic-mode hat.
There was a similar widget made for TMCC level monitoring. That is, a signal level pin was tapped on the 455 kHz demodulator chip which then fed a DC voltmeter. As I recall, you just added a couple components to make it work. This worked because the 455 kHz signal is always present. Hence this is why I think some way to get the DCS signal to be on all the time or at least much more frequent would make it easier to measure.
I have repaired my fair share of TIU over the past few years. I do communicate with MTH Senior Tech who does the majority of repairs at MTH. So here are some points.
TIUs repairs are a small fraction of the repair work compared to engine repairs and upgrades.
After a TIU repair they don't come back for re-repair. I did have one comeback, which I attribute to a faulty component or too much heat when reinstalling (VAR Channel FET)
I have not seen many Rev L with the modified TVS added, though I will pay more attention to this.
Pre Rev L, the Transmit failure was possible, but more likely the Receiver chip took a hit, especially if all channels effected.
A hard hit on one channel transmit chip can cause sufficient of a load on the 5V regulator, that negatively effects all other channels since their input voltage has dropped too low. This is why it is very nice to know what channel was being used when the failure occurred. Otherwise I start removing transmit chips until I find the culprit.
Post Rev L, the receiver chip rarely takes a hit anymore.
You can have a loss of DCS capability, but the TIU transmits fine, but it is receiving the return signal at issue. This can effect half the channels or all of them. Again this is rare.
The only components I have seen damaged are the main power TVS, VAR FET (usually just one of the 4), ACT Transmitter, Receiver Chip, Memory (Rare and usually the very early units), a damaged Aux power jack, fuses and melted terminal housings, and the power inductors over heated and melting changing inductance.
I have only had 2 TIU that I can remember that I could not fix. Early Rev G with a burned up main trace and memory damage, and Later REV L. MTH would acknowledge that occasionally some other unknown component may be damaged that kills a TIU making it not worthy of repair, but this is very, very rare.
My point, For REV L with added TVS for transmit protection, I think Adrien or GRJ device would be acceptable if test shows it holds up better. I don't think it is protecting any other components. Remember this is an add on mod designed to better protect ACT244.
I think the normal home owner and small club environments probably do not see anything like this; though I am sure there are occasional failures.
For those that have failures but keep using the TIU it might make sense your loosing other channels because you have not addressed the faulty component which is still on the buss being powered by the 5V source despite no input power to that channel.
I have repaired ACT244 on Rev L with TVS mod and the DCS came right back, I never tested if the TVS was shorted. I will add this to my procedure, but it is an additional factor, that not all TVS short prior to an ACT244 going bad. G
I have put the ACT244 in three TIU's now, and as I don't see nearly as many TIU's for repair as George, I thought that was a lot of failures. I think I've only had a handful of the TVS diodes on the output fail on the TIU's, so the ACT244 failure is almost as common in my limited sample size.
I'm going to check our club TIU's for signal strength, some of the issues we have with DCS could easily be explained by lower DCS signal amplitude, maybe we have some partial failures that we don't know about.
stan2004 posted:What makes me nervous about the proposed alternative is that the original 1N4148 method was apparently developed in coordination with MTH themselves (?). As I've suggested earlier, I don't believe the MTH clamp is directly on the ACT244 output based on tests Adrian! made months ago. What's my point? While it's been stated that the clamp protects the ACT244, does anyone know with certainty that the clamp doesn't protect OTHER components too? When Adrian! made the oscilloscope tests in the other post, I recall there were other semiconductor components AFTER the ACT244 in the filter circuit.
The diode method obviously does work, I think the object of the exercise is to try to do similar protection with fewer components. The only real way to know if the alternative I proposed will work is for some extended testing in a "real world" environment where we know the failures are happening.
stan2004 posted:But if someone is willing to do the assembly and testing of the direct-on-the-ACT244 method then by all means fire up the soldering iron! I'd also think that one would always want to install clamps on all 4 channels so perhaps the circuit board should have 4 clamps which might save wiring (since VCC and GND) could be shared.
I'm somewhat confused about the four clamps, I thought four outputs were paralleled for each side of the signal. That being the case, why isn't the circuit below sufficient to protect against excursions above and below VCC and ground for both groups of outputs? This should handle one of the ACT244 chips. As for one board servicing all the channels, I thought one of the desires was to keep the wiring short. I wanted this unit to sit on top of the ACT244, one for each channel. To that end, it's only 1/4" wide and .65" long.
gunrunnerjohn posted:...
stan2004 posted:But if someone is willing to do the assembly and testing of the direct-on-the-ACT244 method then by all means fire up the soldering iron! I'd also think that one would always want to install clamps on all 4 channels so perhaps the circuit board should have 4 clamps which might save wiring (since VCC and GND) could be shared.
I'm somewhat confused about the four clamps, I thought four outputs were paralleled for each side of the signal. That being the case, why isn't the circuit below sufficient to protect against excursions above and below VCC and ground for both groups of outputs? This should handle one of the ACT244 chips. As for one board servicing all the channels, I thought one of the desires was to keep the wiring short. I wanted this unit to sit on top of the ACT244, one for each channel. To that end, it's only 1/4" wide and .65" long.
By all clamps on all 4 channels, I mean all 4 TIU channels (Fix1,Fix2,Var1,Var2). So the board could share VCC and GND between all 4 channels and save 6 connections to the TIU board. As for short wire lengths, I was keying off the earlier photo which showed fairly long wires.
I figure the boards were placed where they are because there are no tall components in that area. But as your clamp is placed at a different point in the circuit, perhaps wire length is factor. In which case 4 individual boards would make sense to allow placement directly above the 4 individual ACT244 chips.
I assume your E1..E4 pads line up right above the corresponding pins on a SO-20Wide package allowing placement right on the chip? In which case would it make sense to rotate the E1..E4 pads 90 degrees so only a single right-angle wire bend between board pad and chip pin.
I thought about the orientation of the pads, but due to the small size of the board and pads, I wanted a bit more "meat" soldered to the pad. I hesitate to make the pads smaller as they lose strength in the bond to the PCB material, makes them too easy to pull off. I deliberately made this a one-sided board so there were no traces on the bottom and I could stick it right on the ACT244. One thing I didn't check is the orientation of the ACT244 to see if I had to allow the overhang to be in a different place, or even perhaps have two versions, kinda' left-handed and right-handed to fit on all the chips without hitting anything close. I'll have to "pop the top" of a TIU to check those clearances.
As for the longer wires, I figured any extra propagation delays I introduced with the longer wires would add to the response time of the diodes, so I thought the shorter and more compact edition would work out best. It remains to be seen if this is an effective solution to the issue, but I figured I'd give it the best chance to succeed. Also, his TVS was right at the chip, and now that we're going to likely slower diodes, I didn't want to introduce any extra delay.
By rotating pads I don't see why they would get smaller. I mean like shown in orange:
Would probably mean moving some components around but since you have 4 pins on each side to choose from for the out+ and out-, perhaps not a big deal to slide the middle components around. Also, I would think one way of assembling and installing would be to use solid 24 or 26 AWG (or clipped resistor leads). They would be soldered as shown in red. Then bent down 90 degrees. The board would then be dropped over the ACT244. Then 4 solder joints to the ACT244 pins. I'm sure there are many ways to do this but clearly it's the final attachment step to the ACT244 that will be the hardest part.
Also, maybe also change the white silkscreen from E1...E4 to the actual ACT244 pin numbers such as 10 for GND, 20 for VCC, etc.
It would be easy to move the components, I can do that. I didn't know the pins for the two groups of outputs for sure, are they common on one side of the chip and then common on the other side? If so, I could put the pin number on them, and also locate them directly above the pin in question on the 244 chip.
From this picture, I think I need to have the excess hang-over of the board on the other end, the back of one of the 244's butts up against a large capacitor, the one on the extreme left here. Without opening up one here, I think the four ACT244 chips are the ones indicated, pretty sure that's what I've indicated.
I figure this is yet another chore to verify that relevant revisions of the TIU board group the four left and four right outputs together as suggested here for all 4 channels. Given the ACT244 pinout, it's hard to imagine why you wouldn't group all the lefts together and all the rights together no matter the revision but who knows!
For extra credit, one might research if other DCS devices (DCS Commander, Remote Commander, Explorer, etc.) also use the same ACT244 scheme and hence be candidates for this protection.
I see what you mean about the clearance on the leftmost ACT244.
I suppose the neat thing about your single-sided surface-mount design is you could, for no extra cost, put one style on one side of the board and a different style on the other side of the board!
stan2004 posted:I figure this is yet another chore to verify that relevant revisions of the TIU board group the four left and four right outputs together as suggested here for all 4 channels. Given the ACT244 pinout, it's hard to imagine why you wouldn't group all the lefts together and all the rights together no matter the revision but who knows!
That's what I thought, and I made that "assumption". However, I suspect I should verify it before going to press.
stan2004 posted:For extra credit, one might research if other DCS devices (DCS Commander, Remote Commander, Explorer, etc.) also use the same ACT244 scheme and hence be candidates for this protection.
Interesting point about the other devices. I don't have a DCS-RC handy to check, the only part I see in a fuzzy photo I have is U3, and it looks to be a different pitch part than the TIU. I don't have the Remote Commander or DCS Explorer, so no possibility of checking those.
stan2004 posted:I see what you mean about the clearance on the leftmost ACT244.
I suppose the neat thing about your single-sided surface-mount design is you could, for no extra cost, put one style on one side of the board and a different style on the other side of the board!
I don't see an easy way to convince the PCB layout package to do the trick with two circuits. In any case, since I'd need boards of both designs, I don't see having two different boards as a big deal, they're very cheap. I can't really build both circuits on one board, I can only use one anyway.
Here's a new layout. I had to do double-sided to compress it, but I only need one design now. It's .3" x .52" in size, and it'll perch on any of the 20 pin SOIC packages for the ACT244, no overhang. The pads are labeled with pin numbers, and they're spaced correctly to line up with the corresponding pin on the ACT244. If this works for the needed protection, it would be a compact solution to the issue.
I think you've gone as far as you ought to go until someone steps up to assemble and evaluate.
With either design alternative, I'm curious to see how the costs work out. I figure the component/board costs are negligible compared to labor and cost for 2-way shipping of a TIU. I suspect most guys would want someone else to install these.
As far as evaluating a beta board, we can do that if someone shows the process for us that are technically challenged. We have a scope but only one member knows how to use it and I hesitate to volunteer him with his current load of keeping the wiring functioning in the layout.
Yep, the cost for components and the board should be pretty small. It would be nice for someone with a TIU handy to verify that Pin-17 and Pin-8 are on the two grouped outputs. I am assuming they are since they're on opposite sides, but you never know.
Here's a Link to the latest shared version of the board. MTH TIU Signal Protection PCB at OSH Park
These are the diodes used, quantities in ().
(1) DIODE SCHOTTKY 80V 500MA SOD123
The cost of the parts and the board is less than $3 for a board in small quantities, the board is still 80 cents for three of them, the five diodes are less than $2. I order most boards like this with 2oz copper and .8mm thickness. I get lower impedance traces and thinner boards.
John,
I ordered 9 boards and enough of the diodes and TVS to populate the 9 boards. I will work on soldering them into units and do a test run on a wounded TIU to see if it works.
gunrunnerjohn posted:It would be nice for someone with a TIU handy to verify that Pin-17 and Pin-8 are on the two grouped outputs. I am assuming they are since they're on opposite sides, but you never know.
Not sure what you mean. Your board diagram correctly shows P7 and P18 as being outputs. The close up TIU photos of the mounted ACT244 show the drivers are connected as 4 left inputs driving right 4 right outputs (12,14,16,18), and 4 right inputs driving 4 left outputs (3,5,7,9).
I have an early REV. L TIU that FIXED 1 sends no watch dog signal and cannot communicate with the engine after it's started. All other channels work fine in command mode. Would this be a fried ACT244 on my FIXED 1 channel? I opened it up and don't see any TVS's on the ACT244's unless their soldered on the bottom side of the board. Also, if the problem is a bad ACT244, is it possible to replace it with a socket, to make it easier to replace if it ever fails again?
stan2004 posted:gunrunnerjohn posted:It would be nice for someone with a TIU handy to verify that Pin-17 and Pin-8 are on the two grouped outputs. I am assuming they are since they're on opposite sides, but you never know.
Not sure what you mean. Your board diagram correctly shows P7 and P18 as being outputs. The close up TIU photos of the mounted ACT244 show the drivers are connected as 4 left inputs driving right 4 right outputs (12,14,16,18), and 4 right inputs driving 4 left outputs (3,5,7,9).
Stan, I was asking if the TIU was actually wired with the groups you indicate. I know where I put the pins, but I didn't have a TIU on the bench to see if that's how they were grouped.
Ron_S posted:John,
I ordered 9 boards and enough of the diodes and TVS to populate the 9 boards. I will work on soldering them into units and do a test run on a wounded TIU to see if it works.
If the TIU is already wounded, you may have to replace the 74ACT244 as well. This won't fix cooked outputs, it's only protecting them, or at least the hope is it will protect them.
Dave Zucal posted:I have an early REV. L TIU that FIXED 1 sends no watch dog signal and cannot communicate with the engine after it's started. All other channels work fine in command mode. Would this be a fried ACT244 on my FIXED 1 channel? I opened it up and don't see any TVS's on the ACT244's unless their soldered on the bottom side of the board. Also, if the problem is a bad ACT244, is it possible to replace it with a socket, to make it easier to replace if it ever fails again?
The 74ACT244 is a likely suspect, but it's not really possible to use a socket as it's a SOIC surface mount part. If you look at the first post of this thread, Adrian shows you were they soldered the TVS parts to "protect" the 74ACT244 chips, three were on the top, one was on the bottom. FWIW, with that symptom, that's the first part I go for, I haven't seen the other associated parts fail yet.
gunrunnerjohn posted:Stan, I was asking if the TIU was actually wired with the groups you indicate. I know where I put the pins, but I didn't have a TIU on the bench to see if that's how they were grouped.
OK - I see what you mean. So whoever is stepping up to try your method should take a few seconds to confirm the circuit traces around the TIU look as indicated in the close up photos of the ACT244 chips I posted earlier. The idea there was to show that all 4 ACT244 chips have circuit traces connecting 4 left pins and circuit traces connecting 4 right pins. The red lines show the connections being made by the traces. As it turns out, some of the chips in this particular board are connecting 4 inputs and some are connecting 4 outputs. This doesn't matter so seeing this type of trace pattern is good enough to confirm the desired left right groupings of 4.
That's it, your pictures do seem to suggest they did it the most expedient way, which is obviously what we were hoping. It'll be interesting to see if this is a fix, it would be fairly easy to install if so.
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