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Soundblaster 32 PNP (CT3620) EMU8000 not working

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First post, by audiocrush

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Hi,

I got a troublesome CT3620.
To make it come to life again, I reflowed all the QFP chips on it, and the X3 crystal wasn't producing any clock, until I desoldered L3. That's when I discovered L3 was cracked, so I bridged it with a piece of wire.
Also a handful of caps were damaged so I replaced them.
Starting from that, Soundblaster 16 portion of the card came back to life and I could listen to 8- and 16-Bit FM synthesis.
But when I run diagnose.exe from the soundblaster package, it recognizes everything and the full 8 megs this card can take test out fine, but won't play the EMU samples.
The RAM tests ok though, so something fishy is going on.
What I noticed is, that the CT1745A chip has a lot of bent pins, like it is mounted crooked on the pcb. Almost like the whole chip is turned 2-3 degrees clockwise, but there is no shorts between the pins. Only the 5th pad to the right on the lower edge of the chip seems to have lifted from the pcb, but I cant figure out if it is connected to anything, as there seem to be multiple pads that are not connected.

Also when I go ahead in windows and play a midi file, I can hear a very faint pop, suggesting the audio routing changes in the card, but then no sound is output from the card.

Another weird thing is, that I have to force windows to use the Soundblaster 16 / AWE32 PNP driver manually, if I don't it chooses a XPRESS audio driver for me (which does work but it seems wrong)

Any guesses what could be the culprit?

Cheers audiocrush

https://www.nerdsh.org/ - my blog, a bit neglected though
https://www.youtube.com/channel/UChsU6woi3lhLhtT_ILbSCCw - Some videos of mine

Reply 1 of 5, by Tiido

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Look for an 8 pin Philips branded chip connecting to EMU8000, it is the DAC of it. If there is sound there you can start followng it into opamp+caps and eventually into CT1745 (the mixer chip).

T-04YBSC, a new YMF71x based sound card & Official VOGONS thread about it
Newly made 4MB 60ns 30pin SIMMs ~
mida sa loed ? nagunii aru ei saa 😜

Reply 2 of 5, by audiocrush

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Thanks man, I'll check it out!

Also I tried to measure the broken inductor L3, it is very hard to get a good connection but it seems to be around 16mH, is that realistic? it is quite large for an smd inductor...

*edit*

meeh unfortunately no philips chip in sight. 🙁

Attachments

https://www.nerdsh.org/ - my blog, a bit neglected though
https://www.youtube.com/channel/UChsU6woi3lhLhtT_ILbSCCw - Some videos of mine

Reply 3 of 5, by Tiido

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I'm not sure what value is normal for the inductors, I have not tried to measure them and for now I cannot either since my hardware is packed away from the recent move to another country 🤣

They DACs are right next to the main oscillator and CQM chip just above 16bit part of ISA slot. One is for EMU, other is for CQM.

T-04YBSC, a new YMF71x based sound card & Official VOGONS thread about it
Newly made 4MB 60ns 30pin SIMMs ~
mida sa loed ? nagunii aru ei saa 😜

Reply 4 of 5, by audiocrush

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I tried to measure the other ones in circuit but it doesn't seem to work 😁

Oh, I hope the move went well then?

I'll check out the DACs later, I was focusing on the area around the EMU but there weren't any, didn't know you meant the other ones.

There is good news however:
I hooked up my oscilloscope to the SPDIF output next to the EMU and I get a 7V square wave, and once I start playing a midi file the square wave starts doing all sorts of funny things.
I don't have a SPDIF device handy but it looks to me like that is data 😁

https://www.nerdsh.org/ - my blog, a bit neglected though
https://www.youtube.com/channel/UChsU6woi3lhLhtT_ILbSCCw - Some videos of mine

Reply 5 of 5, by Tiido

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Yeah, in-circuit measurement of capacitors and inductors is inaccurate at best.

Move itself went well, the stuff afterwards have been more trouble 🤣. Settling in goes slowly, partially because space is an issue.

EMU is definitely alive then. Next up is investigating the DAC and path to the mixer then. EMU and FM share the input so this narrows things down to DAC and whatever does the mixing of the two sources into one signal.

T-04YBSC, a new YMF71x based sound card & Official VOGONS thread about it
Newly made 4MB 60ns 30pin SIMMs ~
mida sa loed ? nagunii aru ei saa 😜

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