Failed Sound Chip on 5V Board?

You mean the audio amplifier- yes, replaceable.  A search in the forum came up with this post below.

@gunrunnerjohn posted:

The PS/3 amplifier is a WM9081 2.6 watt class AB/D amplifier.

The 3V PS/2 amplifier is a TPA2000D1 2 watt class D audio amplifier.

The 5V PS/2 amplifier is a TDA7056A 3 watt audio amplifier.

In my experience, the through hold desoldering with the nearby SMD components is what makes this replacement pretty hard. It's just a lot of components placed as physically close as possible.

Here is a shot from a PS2 5V repair topic https://ogrforum.com/topic/pro...d-2-5v-board-repairs

The amplifier is the one with the large heatsink tab vertical near the output connectors. You do not have to desolder the board stack- this is just a quick picture I found showing the location.

The sound chip on the 5V board is the large SIP package at the end, they are available and can be replaced.  I've stuck a few in, but it's been a while since I had one come in for that issue.  The chip is the TDA7056B, Amazon has them.

I just flex the old one to break the leads, then desolder them one at a time.  That makes this kind of repair pretty easy.

Hey thanks Vernon and grj; great info! That looks pretty doable so I’ll get a couple on order.

I assume it has failed because the sounds dropped out while running and were replaced by a steady audible buzzing kind of sound. It has about 10 hours on it. And it would be a shame to trash an otherwise good board for a failed sound amp!

Check the speaker first, they're a common failure.

@gunrunnerjohn posted:

Check the speaker first, they're a common failure.

Thanks John. There is an audible humming you can hear (even a half-deaf guy can hear!), so I figure the speaker is OK. It wouldn't be something that simple haha!

So here is my take on 5V board repairs having read through everything here, including the previous OGR topic that Vernon attached:

1. Many parts on the backside of the larger bottom board can be replaced. This includes all FETs for lighting, smoke unit control, etc.

2. The large sound amp chip can be replaced; part TDA7056B.

3. Accessible aluminum caps can be replaced if bulged or burnt appearing.

4. Separating the two boards to get to a failed part is likely not feasible; not repairable.

5. If the board is shorted out it could be a short between board layers; not repairable.

6. If you are powering two smoke units, upgrade Q307 and Q311 to BSH101 and IRLL2705 parts respectively.

7. Early 2000-2001 seem to be the most failure prone. Later boards seem to be more reliable.

8. If its dead, leave it dead. Bury it and move on.

What's interesting is I have maybe 6-8 diesels, mostly multi F units, as well as a similar number of steam, all from 2000 to 2004 that are still working fine. Mind you they don't get a lot of "hard" use or lengthy running sessions. My recent dead slave board and now this sound issue are the first 5V problems I have had.

I have noticed on ABA sets that after about say 1/2 hour of running, the lead shell is noticeably warm to the touch, whereas the trailing unit shell is quite cool. Maybe the biggest enemy of the master board is excessive heat?

Another question: how are the couplers controlled? I don't see any data as to what controls them.

Well, the 5V boards pull considerably more power than the 3V boards.  That's both at idle and running.  The 5V boards just run hot.

@Rod Stewart posted:

Another question: how are the couplers controlled? I don't see any data as to what controls them.

They are commanded from the lead unit.  The coupler connection in the slave comes off pin-6 of the eight pin connector, and it comes across the 10-pin tether from the master.

@gunrunnerjohn posted:

Well, the 5V boards pull considerably more power than the 3V boards.  That's both at idle and running.  The 5V boards just run hot.

They are commanded from the lead unit.  The coupler connection in the slave comes off pin-6 of the eight pin connector, and it comes across the 10-pin tether from the master.

Sorry, I meant which board component on the master PS-2 board actually triggers the F coupler? The trailing A unit slave board would have a similar device for the R coupler presumably.

@Rod Stewart posted:

Sorry, I meant which board component on the master PS-2 board actually triggers the F coupler? The trailing A unit slave board would have a similar device for the R coupler presumably.

Actually, they send the rear coupler pulse through the tether to the rear, the master is doing all the work.

@Rod Stewart posted:

Sorry, I meant which board component on the master PS-2 board actually triggers the F coupler? The trailing A unit slave board would have a similar device for the R coupler presumably.

So basically right there where you wanted to replace the audio amplifier.

https://ogrforum.com/topic/192...1#192886122952331501

Credit to George- GGG

Here is the PS-2 5V coupler Transistor (Not FET).  It sits behind the audio chip on top of the processor board.   The top power section is removed along with other components.  You can clearly see the traces from pin 8/9 of the 12 pin going to legs 5/6 and 7/8 of the transistor.

Vernon, thanks for that coupler chip info, and to GGG originally. I pulled the number and found the data sheet and ordered a few on ebay for stock, since it does appear to be a serviceable part. (Digikey have no stock) Its called a dual n-channel mosfet and can handle a continuous current drain of 3 amps. Wow!

After all that excitement I went downstairs and just for fun powered up the offending AA set. Guess what? It sounds just fine today; working perfectly. it ran for perhaps 40 minutes and never missed a beat; though I was expecting dead silence at any moment. Strange or what? But the jury is still out; it could croak for good any time.

Next I took a closeup pic of a 5V board stack, below.

In the upper left area you can see the pins where the two boards join electrically. Those pins look similar to the same kind of thing used extensively in TMCC days for plugging board together. I have not tried to pry them apart since this board set is running fine. But are these the pins that cause all the trouble separating the boards?

Anyway, thanks to all for the help!