Weak or NO DCS signal from TIU

the revision with which your talking about was only for the rev L tiu older ones were built slightly different and did not have the same problem with 244 ic's  but rather with the max 4639!

Alan

If you have varying signals on the channels, that's likely the ACT244 chips.  The MAX 4639 would likely be a digital event, either no signal or normal operation.

Does anyone have the correct Digi-Key part number to replace the ACT244 chip. I have one channel functioning with Variable voltage but will not emit a DCS signal.

Drop me a line and I can fix you up, I have tons of them in stock.

It is not as simple as you think.  I have seen all sorts of combinations of defects have an effect on the TIU function.  In the end the only thing that matters is can the TIU transmit and RECEIVE the signal back.  I have seen the TIU transmit the initial watch dog pulse, but not the longer sustained one once the TIU finishes starting up and flash the LED ID #.  I have seen a single transmit chip effect other channels, I have seen partial receive chip function, I have seen receiver chip effect Transmit output, and the combination goes on and on.

The MTH guidance in ASC manual was before an actual device to look at output.  Techs did not have oscilloscope (except John:-)).  So it was a logic chart.  Early models more susceptible to receiver failure.  Rev L more susceptible to Transmitter failures.  BUT I do see both on Rev L and sometimes together.

The simplest is when one channel does not work but all the others do.  The worst is none work and LED barely lights or the current draw is high just TIU.  This means a short that is effecting the Power Supply.  So you can pull all the transmit chips and if still present pull the receiver.  If still shorting change the 5V reg, if still shorted, look for round object with lid and deposit TIU in the object.

@GGG posted:

If still shorting change the 5V reg, if still shorted, look for round object with lid and deposit TIU in the object.

I deposit them in my dead TIU box for spare parts.

@gunrunnerjohn posted:

I deposit them in my dead TIU box for spare parts.

A veritable graveyard 😉

From this post and others, I have picked up many good suggestions for trouble shooting TIU issues.  It has been interesting trying to keep the clubs 14 TIUs (8 active, 6 spare) operational. summarized below are some of the TIU trouble shooting problems and" POTENTIAL" hardware causes I have picked up from the various threads.  Before addressing a potential hardware problem make sure that all TIU software setting are correct.

-Variable channels with low or no track power output, potentially a bad power FET (IRFZ44)

-Track power short on the output of any of the TIU channel, most likely a bad TVS which has shorted out (1.5KE33)

-Low or no DCS signal output on any one channel, potentially a bad transmit chip (ACT244 )

-No DCS signal on any output channel, potentially a bad receiver chip (MAX 4639). The Max4639 receives only track signal from a DCS engine

If anyone wants to add, correct or update the above list, please do.

Thanks to all the contributors,

Bob D

NJ-Hi Railers

Add one more,

Variable channels with constant ON track power output, most likely a bad TVS which has shorted out (1.5KE51). These are in parallel to the MOSFETS so when they short, even if the MOSFET is off, you get the full voltage out bypassing the control by the MOSFETS.

FWIW- Zcontrollers have the same (1.5KE51) in the same arrangement in parallel to the variable control MOSFETS and have the same result- constant output regardless of handle position when that TVS fails shorted. Picture and details here https://ogrforum.com/...4#154167236021571964

My method is to use a side cutter to clip one end of the TVS diode leg and then check with a meter when you have one suspected shorted. This removes it from the circuit but still allows you to test the device with a meter. Again, the problem is, we have more than one device in parallel that might have failed- so disconnecting the cheapest and easiest one to replace (2 leg diode VS 3 leg MOSFET).

-No DCS signal on any output channel, potentially a bad receiver chip (MAX 4639). 

Not true, but possible.  Channel that transmit, but can't receive return signals can be the receive chip.   G

@GGG posted:

-No DCS signal on any output channel, potentially a bad receiver chip (MAX 4639).

Not true, but possible.  Channel that transmit, but can't receive return signals can be the receive chip.   G

Thanks GGG for commenting.  Can you elaborate?

I have a TIU that will transmit the watch dog signal on all channels when I first turned on TIU power.  But when I use the hand held, both tethered & wireless, I don't  get any TUI output signal.  Also, can't change the TIU number.  I changed the MAX 4693 receiver chip which seems to be common to all channels, but that didn't help.  Are there any other  components  that are common to all channels that would prevent an output signal when the hand held is used?  

Thanks,

Bob D

Not being able to change ID address or communicate with TIU has nothing to do with the DCS transmit and receive chips that communicate with the engine.  Sounds like some other fault, and that may not be repairable.

If a TIU can transmit the watchdog.  The transmit chips are probably fine.  If you can not load an engine or receive a DCS signal strength response from an engine already loaded, that could be receiver chip.  For example an engine loaded can be started.  But can't respond when necessary.  Transmit fine, receive not.  Being able to load an engine requires a transmit signal, and the receive signal from the engine.  G

How about a scenario where: the engine will load and start. Engine will run, cannot get engine lights to respond and horn/whistle may be intermittent. Smoke takes multiple remote or app hits to make a change. Test signal only reading 6-7. ACT244 chip? 2 other TiU channels in use read 10s with no issues.

The only time I get a signal reading on the scope of any type, is when I first power up the TIU.  When I use the handheld tethered or wireless, I don't see any output signal response on the scope for any of the channels, not transmitting at all.  That's why I thought the problem might be a faulty MAX4693 receiver chip which was not receiving commands from the handheld, so the TIU would not transmit anything out and not execute internal commands to the TIU.    Is there a way to trace the signal in the TIU or does anyone have a schematic of the TIU.  Any suggestions?

Thanks

Bob D

The MAX4693 has nothing to do with the wireless remote communication, it's receiving the DCS track signal coming back from the engines.

@Vernon Barry posted:

Add one more,

Variable channels with constant ON track power output, most likely a bad TVS which has shorted out (1.5KE51). These are in parallel to the MOSFETS so when they short, even if the MOSFET is off, you get the full voltage out bypassing the control by the MOSFETS.

FWIW- Zcontrollers have the same (1.5KE51) in the same arrangement in parallel to the variable control MOSFETS and have the same result- constant output regardless of handle position when that TVS fails shorted. Picture and details here https://ogrforum.com/...4#154167236021571964

My method is to use a side cutter to clip one end of the TVS diode leg and then check with a meter when you have one suspected shorted. This removes it from the circuit but still allows you to test the device with a meter. Again, the problem is, we have more than one device in parallel that might have failed- so disconnecting the cheapest and easiest one to replace (2 leg diode VS 3 leg MOSFET).

Thanks for the additional information and this could be a way to resolve the problem of replacing bad MOSFETs when the variable channels are used as fixed channels.  If the two variable channels are always used as fixed channels, and a MOSFET goes bad, any issue of just jumping the TVS so now you are just getting full transformer voltage at the output of the TIU channel?  

@rad400 posted:

Thanks for the additional information and this could be a way to resolve the problem of replacing bad MOSFETs when the variable channels are used as fixed channels.  If the two variable channels are always used as fixed channels, and a MOSFET goes bad, any issue of just jumping the TVS so now you are just getting full transformer voltage at the output of the TIU channel?  

I would not recommend that. The TVS was there in an attempt to protect against voltage spikes. It's not there as a primary current path. If you are having events that would kill the channels (derailments, overloads, shorts, inductive kickback spike events) that caused the original failure and then now passing primary current through a path meant to be for protection seems like a really bad idea.

Ideally, just use passive mode and external inductive choke and bypass the entire power section. and any  power going through the TIU.

I have replaced only 1 of those TVS during my career of fixing TIU.  As far as jumpering the VAR Fet for constant Fix, yes it can be done.  Believe a few clubs do that.  What you loose is emergency Kill feature since only Fix channels protected by Relay.  The VAR turn off the FETs, which are now jumpered.

You did read my post about the receiver chip versus your issue of non communication with TIU?   The remote and TIU have a transceiver board for communication between remote and TIU.  Engine is done over the track.  G

@GGG posted:

You did read my post about the receiver chip versus your issue of non communication with TIU?   The remote and TIU have a transceiver board for communication between remote and TIU.  Engine is done over the track.  G

G - Yes, thanks for the clarification.   ACT244 transmit chip & MAX 4639 receive chip handles TIU to track/engine communication.  The plug-in transceiver board handles the air link communication between TIU and handheld.  

Where does a tethered hand held get connected into?

Thanks, Bob D