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Soundblaster Pro2 CT1600 detected, no sound

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First post, by Michiel79

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Hi there,

I put together a 486 for DOS gaming.

Specs are as follows:

Mitac board, IH4077D. Efar chipset.
486 DX4 100Mhz (33X3) As shown by the CPU check tool.
SB PRO2 CT1600
3com NIC, for WIn3.11 networking. Mainly for ftp'ing tools/games/drivers to the 486.
Added a battery (cmos) to keep bios settings.

Everything worked like a charm. Benchmarks were on par with what it should be.

I stored the 486 for a while. Left it in a cool dry place where nothing could harm it. After a good six months I decided to power it up again.

At first, two problems:

* No sound, what so ever.
* Also, mouse not working (serial microsoft mouse, com1).

Sound: Autoexec.bat has the setblaster set at what the jumpers on the sound board are configured at. The creative driver tools (SBP-TEST) can detect it. Found at 220, dma1, irq5. As set by the jumpers on the card. Mixer tool shows that nothing is muted. Everything at max. Tried different Creative tools that test/play sounds, but nothing. Starting wolf3d shows that a soundblaster is detected, but, as stated, no sound. Yes I'm using the speaker output, but of course I tried every output to be sure. AIDA also finds the SP-pro2 at 220/i5/dma1. I tried different speakers. No dice.

Then I tried a CT2960, a PnP card. Installed the SBbasic16 driver, together with CTCM. CTCM detects it. CTCU finds no conflicts. But again, no sound.

- could it be a bios setting?
- AT bus clock maybe? Currently at clck/4, so 33/4=8 mhz. Should be ok?

No mouse. Tried two different serial mice, a Tulip one, and a MS mouse. I have a multimeter. I checked the voltages on the pins of the com port. There's ~-10volt on pin 3. I tried that to make sure the powersupply is sending -12v to the board. Tried CTMouse of course, and a MS driver for the Microsoft mouse. Nope. MSD states that no mouse hardware is found. Mouse driver is mapped to IRQ4, used by com1, as stated in the IRQ overview in MSD. LPT1 is switched off. NIC is using IRQ10, as stated by that driver.

These two issues are of course completely different, but both of these things stopped working, at the same time.
Could these two issues (sound and mouse) be related? Is the motherboard on it's way out, or the powersupply, or both? Any voltages I could test? I have a multimeter.

Any ideas/suggestions are much appreciated!

Here are some photos of the configuration: BIOS settings, MSD diagnostics.

https://imgur.com/a/FwfwiIr

Last edited by Michiel79 on 2021-11-30, 07:09. Edited 1 time in total.

Reply 3 of 8, by SpocksBeer

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The SB Pro at least needs -5v to function, so check that rail on the PSU. -10v seems kinda weird, nothing would be generating that from the PSU, so perhaps you have a general issue with the negative voltage rails

Reply 4 of 8, by Michiel79

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SpocksBeer wrote on 2021-11-30, 10:25:

The SB Pro at least needs -5v to function, so check that rail on the PSU. -10v seems kinda weird, nothing would be generating that from the PSU, so perhaps you have a general issue with the negative voltage rails

Thanks for that tip. How do I check that, exactly? The main powersupply plug that goes into the motherboard?

Reply 5 of 8, by mpe

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I don't believe SB Pro (CT16xx) cards need -5V. Older Sound Blasters do (like SB 2.0 ct1350b or earlier)

You can clearly see that the -5V pin is not present on the PCB:

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Reply 6 of 8, by SpocksBeer

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Well, there you go. Had that wrong in my head. Anyway, still good to check all the voltage rails at the AT plug on the motherboard.

After that, try removing everything you don't need to make it boot (minimum expansion, drives, ram) and see if there's any change in behaviour. Focus on one problem at a time as they might still be related.

Reply 7 of 8, by mkarcher

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SpocksBeer wrote on 2021-11-30, 10:25:

The SB Pro at least needs -5v to function, so check that rail on the PSU. -10v seems kinda weird, nothing would be generating that from the PSU, so perhaps you have a general issue with the negative voltage rails

The OP was talking about having -10V at a pin of the serial port. This sounds about right. The output driver chip is supplied with -12V, but some voltage "gets lost" in that chip, so -10V appears on the output. On the other hand, having a sound card and serial ports (mouse) fail at the same time puts some suspicion on the -12V rail, as that rail is used by the serial port drivers as well as classic analog op-amp circuits on sound cards.

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