Help with Yamaha ABC channel audio

[Frank.Bullitt]

Hello,

 

I've got an Atari 1040STE, I plugged in the left and right audio jacks the other day, and I'm not able to get audio from the Yamaha sound chip.

 

I have removed the YM sound chip and placed it back in, no luck.

 

I have recently been replacing the capacitors in my ST with Rubycon Aluminium caps of the same value, I can't see any errors in what I've done, negative and positive sides all match up.

I've also replaced the PSU, but this has been running smoothly for a couple of weeks.

 

Can anyone give any indication as to which capacitors could cause this issue, or any other help in fixing my ST?

 

I've attached a video of the STE V1.9 test running from a diagnostic cart I purchased from Exxos.

[Zogging Hell]

Is there sound coming from the monitor port (mono) on pin 1 (iirc). If so then the sound chip is probably ok. I have never used separate speakers with my STe, although have tapped the output into my Phillips monitor, but believe the sound they produce needs to run through an amplifier, so I don't know if you were doing this?

 

If not you will probably need to trace back from the audio outs until you find the culprit.

[Frank.Bullitt]

13 minutes ago, Zogging Hell said:

Is there sound coming from the monitor port (mono) on pin 1 (iirc). If so then the sound chip is probably ok. I have never used separate speakers with my STe, although have tapped the output into my Phillips monitor, but believe the sound they produce needs to run through an amplifier, so I don't know if you were doing this?

 

If not you will probably need to trace back from the audio outs until you find the culprit.

I tried using the mono audio out on this VGA adapter, it has a 3.5mm socket, unfortunately the same issue occurs.

[Zogging Hell]

An audio probe might be helpful to trace back the signal so far. It could be something simple like a broken track. The sound chip also drives some other functions in the ST so if the sound is your only issue then I suspect the fault still lies somewhere else. I believe the sound chip output is mixed with the DMA sound system at some point on the STe (I may be mistaken this is above my pay grade on the ST internals, hopefully someone with a bit more knowledge can chime in). I did manage to kill the sound chip in my Falcon by trying to drive a scanner through the parallel port back in the day, so perhaps trying to check to see if you can also print may also give further clues.

[Frank.Bullitt]

I kept the capacitors that I replaced in a bag, and looking at them now, two of them say NP. Their value is 4.7uf 35v. I think I've replaced these with polarised caps of the same value.

 

This is likely to have caused the issue, as non polar caps are used in audio equipment if I'm not mistaken?

 

I've ordered some replacement caps from Mouser as I can't find any on Farnell, I hope they come tomorrow. Really want to finish off my ST project by the weekend so I can play some classic games LOL.

Edited August 13, 2020 by Frank.Bullitt
Spelling error

[Frank.Bullitt]

Hello again,

 

If anyone has a 1040ste, could you tell me how many non polar caps they have on their board?

 

I've only found two, but I'm afraid I may have misplaced one, as there are currently 3 caps that I have replaced that are valued at 35v 4.7uf.

 

If someone could let me know I'd be really really grateful.

[zzip]

On 8/12/2020 at 6:30 PM, Zogging Hell said:

I believe the sound chip output is mixed with the DMA sound system at some point on the STe (I may be mistaken this is above my pay grade on the ST internals, hopefully someone with a bit more knowledge can chime in)

Yes that is correct, it seems to be the LMC1992 chip that does this.

 

If you look at the page below, under figure 6, it says that certain values sent to LMC1992 will disable YM2149 sound.  It might be worth checking to see if this is occuring

https://info-coach.fr/atari/hardware/STE-HW.php

 

 

[Frank.Bullitt]

Hello again all.

 

I've replaced the capacitors with non polar Nichicon's of the same value, still no sound.

 

I've tried tracing from the YM sound chip and the LMC1992 chip, and I'm not able to figure out what is wrong.

 

is there anyone on the Atariage forums in the UK that does repairs for ST's? I have to hold my hands up at this point and say I haven't got a clue lol.

[Chri O.]

In Post #6 you show 3 pictures with some capacitors, all of these capacitors point to TL497A IC#107 at least in Atari STe Schematic (Rev A, C300780-001).

The TL497A switching voltage regulator operate in numerous voltage-conversion applications (step-up, step-down, invert) with as much as 85% of the source power delivered to the load.

I wonder if you screw up here somehow (lose connection maybe, bad soldering job ) perhaps you ripped the trace while you were trying to desolder the old caps?

 

Just ignore the first picture I'm having difficulties with Windows 10 and few beers ?

[Frank.Bullitt]

1 hour ago, Chri O. said:

In Post #6 you show 3 pictures with some capacitors, all of these capacitors point to TL497A IC#107 at least in Atari STe Schematic (Rev A, C300780-001).

The TL497A switching voltage regulator operate in numerous voltage-conversion applications (step-up, step-down, invert) with as much as 85% of the source power delivered to the load.

I wonder if you screw up here somehow (lose connection maybe, bad soldering job ) perhaps you ripped the trace while you were trying to desolder the old caps?

 

Just ignore the first picture I'm having difficulties with Windows 10 and few beers ?

Thanks for this, I'll have another look when I get home from work tonight. The capacitors in post #6 have been replaced with non polar capacitors, as I made a mistake there.

The background colour on the STE diagnostic software is now blue instead of orange, but other than that no changes to the sound.

[Zogging Hell]

If you've hit a brick wall you may want to try posting on Atari Forum or Exxos's forum, you'll most likely find more advice there and potentially someone to fix it. There was a thread recently on people that might repair your ST in the UK on Atari Forum iirc.