Amiga A600 - No audio in SOME games and demos.

[jbh1977]

Hi all. Bit of a weird one... Have searched high and low, but I can't find anyone ever having this problem before...

I have an A600 (rev 1.5), upgraded to KS 3.1.4. In some games and demos the audio works great on all four channels. In others though, there is complete silence. This is very consistent between different software and it's not a case of 'intermittent' audio.

The classic State of the Art demo is particularly interesting, because it clearly plays the thud thud thud when the title appears but there is no music and the rest of the demo is silent.

In Amiga Test Kit I can hear all four channels loud and clear, whether or not the filter is on, so it's not that.

I have tried different audio cables, and even a different TV. I've tried two different power supplies. The PSUs are outputting the correct voltages on each pin.

I know what you're all thinking, and yes, it has just been re-capped. I should point out though, that this fault was apparent before AND after the re-cap, so I don't think it's a cap issue. There was no obvious leakage or damage. Perhaps some slight darkening on a couple of traces but these check out ok with a multimeter. While I had the meter out I checked the AVREF voltage which was 2.3 - which is near enough what it should be.

Anyone have any ideas? I have just purchased a Furia accelerator and I am keen to get going with some WHDLoad goodness!

[jbh1977]

I've cracked it.

I can't believe I missed it. Hiding under the floppy cable, pin 23 on the CIA chip looks like it's never been soldered properly. It must have left the factory like that and I'm surprised the previous owner never noticed.

Have checked the schematics, and this is for _INT6, whatever that is. All I know is it goes to the expansion port, and also the Gayle chip. I guess some devs use certain interrupts to play audio and others don't. That would explain it only worked some of the time.

All I know is that when I bridge the joint, the audio springs into life. When I get a chance I'll re-flow it properly and I'll be cooking on gas. Am just glad I haven't had to replace Paula or something because I was not looking forward to that!

[psoma]

Wow... good find!!

[jotd]

Phx ptreplay (and probably others) uses level 6 interrupt to play music/sfx. Other trackers just use level 3 (vertical blank). Nice story!

[solarmon]

@jbh1977

An interesting symptom and root cause!

Also interesting that audio could be played through/using other interrupts, other than level 4 (as per https://wiki.amigaos.net/wiki/Exec_Interrupts)

Didn't a CIA test in Amiga Test Kit show up any issues? (I don't know if/how it tests interrupt levels and how interrupt issues could manifest itself in the CIA tests).

[jbh1977]

Originally Posted by solarmon

Didn't a CIA test in Amiga Test Kit show up any issues? (I don't know if/how it tests interrupt levels and how interrupt issues could manifest itself in the CIA tests).

@solarmon As a matter of fact it did but I'd seen spurious errors before, so I didn't connect the two things straight away. Should have noticed it sooner but the chip was hidden by the floppy cable. That's my excuse and I'm sticking to it!

All fixed now and sounding great.

Pics and video here: https://twitter.com/jbh1977/status/1269293287371931648

[solarmon]

I was curious, so I tested the same issue and isolated pin 21 on the Even CIA on my A500.

I was able to boot ATK OK. Latest ATK v1.9 has a new mod tracker feature in the Audio test section and the mod tracker music was not working until I bridged pin 21. Although, the tone test (500hz Sine) was still working - as it probably doesn't use/require INT6.

The CIA tests when INT6 is not available to the Even CIA shows the following errors:



Another good one for the knowledgebase!

[jbh1977]

The really strange thing is, it looked like it had always been like that. Perhaps that's why the previous owner was so keen to get rid of it! I did notice it doesn't have a burn-in sticker, and it does make me wonder how well these machines were tested at the time...

It wasn't until somebody else pointed out the CIA errors that I started looking more closely at those chips. Until then I was starting to think about replacing Paula, which was something I really didn't want to do.

At least it works now, that's the main thing. It's been re-capped too, which would have needed doing anyway.

Am glad it was such a simple fix. The answer really was right under my nose. If anyone else finds this story useful then I'll be glad to know I've helped in some small way.