CPS3 Sound problem

[yavuzg]

I've resurrected my second CPS3 system (by converting 4 x 32Mbit SIMMs into 2 x 128Mbit SIMMs and an extra 128 sourced by Darksoft - thanks btw). The system works fine but with very "scratchy" distorted sound from the JAMMA sound. I tested the line-out (connected to Commodore 1084 monitor - just with RCA extension cables) and the sound output is as pure as angels singing

I first suspected the strangely "loose" volume pot. I changed it with a bulky ordinary 10K stereo volume pot but didn't get any change. Still distorted, "hissy", "scratchy" sound. Oh btw, the pot seems fine internally and the "loose" feeling was because the volume knob has been broken internally. I repaired it later with some epoxy glue but I don't know this repair would last. Ordered a new one from Aliexpress - there was only a single guy selling it $11 per piece - total ripoff but I want my PCBs repaired complete and as original as they should be. Anyway, if anyone is interested, the part for the original volume pot for the CPS3 is; ALPS RK09 I'm not sure about the dimension though. I'll let you know in a month!

Anyway, I then suspected the electrolytic capacitors but just felt too lazy to change all of them because my automatic solder sucker just died on me and since the line-out is OK (there are also electrolytic caps on the line-out part as well), I just thought the caps might be still OK... I mean, if some are OK the rest might be OK too (very lazy thinking I know )

My next victims were the sound amplifier IC and the two 0.15uF polyester capacitors. The amp IC and the two polyester caps are the only components directly connected to the JAMMA edge (L and 10). I already ordered the amp IC (which was ridiculously cheap - $1 + VAT ) and the caps locally online.

Tomorrow when I get the package and have time to replace the suspected components I'll let you know the results. But in the meantime, if you have any other suggestions, I'd be glad to listen...

 

[yavuzg]

OK. Update...

Changed the 0.15uF polyester capacitors first (Used 150nF 100V ones). New ones look nicer but didn't solved the problem.

Next, changed the amplifier IC. Bingo! Now I got pure sound from JAMMA as well...

So, for the reference, if you have distorted sound with lots of background "hiss" noice from JAMMA and if playing with the volume pot does not seem to have a positive/negative effect AND you have stereo audio on the line-out RCA connectors then change your amplifier IC!

The part number is; Toshiba TA8201AK


It is a very cheap (price-wise) mono audio amplifier IC generally used in car audio systems back in the day (That's probably the reason I can still find it easily even in local electronics parts shops for $1).

Generally, having stereo output from the line-out RCA connectors is a good indication that your sound data on the SIMMs are OK, do not have digital-analog conversion problem, electrolytic caps most probably OK, your pre-amplifier ICs (LM833) are OK etc.

 

[Mitsurugi-w]

Good info! Thanks for sharing.

 

[nonosto]

I have the same issue when I touch the volume pot, do you think must change volume pot too or only ampli? I found Toshiba TA8201AK but where can buy a volume pot and service button too.

 

[yavuzg]

I have the same issue when I touch the volume pot, do you think must change volume pot too or only ampli? I found Toshiba TA8201AK but where can buy a volume pot and service button too.

If your sound problem is "only" related with the pot, touching it would result as good sound/bad sound/no sound. Just change the pot. If the problem is "only" related with the amp then you should still be able to get good sound from the line-out RCA connectors.

Regarding the "service button" you mentioned; I guess you are referring to the "TEST" button on the PCB, right? It is an ordinary tactile button. I don't know the exact part number but any tactile button of correct dimension would work. You should find them from any hobby/robotics/arduino shop or online... Btw, if your cabinet/supergun/jamma setup has a test button you don't need the test button on the PCB. I mean the button on the PCB is not a "special" button, just a switch connected to the JAMMA edge pin 15...

 

[nonosto]

THX buddy. you are in right I have problem sound with rca output, when I touch the pot. So if you have one or 2 pot to sell for me please. For test button it's just cosmetic.

 

[tacobell]

What if you’re getting scratchy sound coming from the RCA output? Would replacing Toshiba TA8201AK still work?

 

[nonosto]

you must change sound post for a new, ref: ALPS ロータリボリューム RK09K12

 

[tacobell]

Ended up changing ALL the caps, the sound amp IC AND the alps rk09 pot with a brand new one and still no change. Still sounds scratchy.

 

[tacobell]

So this is a very weird case. Ended up replacing both LM833N chips after replacing all the caps, sound amp IC AND alps rk09 pot. Unfortunately, the cracking still persists.

However, I accidentally increased the voltage on my power supply and notices the audio cracking was mostly gone!

Based off the HAS, the cracking disappeared past 5.30v:

Anything under that you will hear some static. Anything under 4.90v starts to crackle a bunch.

This worries me because this should be running at 5v.

Does anyone know if that is normal to run that hot on the CPS3 or if there are any parts I need to replace other than the ones mentioned?

 

[tacobell]

On the Toshiba TA8201AK equivalent (NTE1832) I measured 4.84 on pins 1-3, 6.19 on 5 & 7 and 12.86 on pin 6 VCC at 5.32v on the power supply!

There is barely any audio cracking but it happens rarely. This worries me because of how hot it is and yet not powering up thr sound amp to spec. What is causing this chip to be under powered?

 

[kikaso]

Maybe the HAS voltmeter lacks proper calibration?

Use a multimeter to measure the voltage at the JAMMA edge and adjust the power supply so that the JAMMA edge reads 5V.

 

[tacobell]

Maybe the HAS voltmeter lacks proper calibration?

Use a multimeter to measure the voltage at the JAMMA edge and adjust the power supply so that the JAMMA edge reads 5V.

This matches the multimeter. It’s 5.3v at the jamma edge unfortunately

 

[kikaso]

That’s a lot of voltage drop from Jamma edge to a chip. Do any other chips behave this way in terms of voltage drop?

 

[tacobell]

That’s a lot of voltage drop from Jamma edge to a chip. Do any other chips behave this way in terms of voltage drop?

I haven’t tested any other chips, but it’s been happening prior to any modifications I’ve made to it. @Derick2k is aware of this issue as I’ve purchased the board from him. We’ve been trying to pinpoint this for a couple years now, but it’s only now I’ve had the time to go over it.

@kikaso if you got any hints, let me know. The only other chip I hadn’t replaced, but was suggested by @Derick2k was the TSOP TDA1306T but I highly doubt replacing that it would help considering the voltage is dropping

Either way, this sound issue is way above my skillset so if anyone else got hints, I’m definitely gonna take them and add to this thread. Hopefully, this can be solved.