386SX board will not work with most sound cards...

Discussion about old sound cards, MIDI devices and sound related accessories.

386SX board will not work with most sound cards...

Postby Ozzuneoj » 2019-1-14 @ 04:00

This has me pretty much baffled. I'm going to keep it short.

Short Version:

In my 386 system my SB Pro2 CT1600 and CT1740 work fine. SB 2.0 CT1350B, MediaVision Thunderboard and Aztech SoundGalaxy BXII (8bit card) all give me no FM music or sound other than a static\buzzing sound when the speakers are turned up high and it does not change with activity on the computer. All are set to IRQ5 and address 220, just like the CT1600 and CT1740. MediaVision PAS16 is not detected at all by several DOS installation programs and will not work at all. Tried with both an original AT power supply and a modern one with an AT-ATX (with -5v) converter, same problem. All of the 8bit cards work flawlessly in a PII 400Mhz system (using an ATX 24pin to ATX 20pin with -5v converter). Originally thought it was related to the OSC clock pin, but I'm unsure since the CT1740 has this pin as well and it is connected to something.

DTK Datatech AM386SX 33Mhz Motherboard with 128KB cache installed (More info about this board here)
Diamond Speedstar VGA Tseng ET4000AX
SIIG Enhanced IDE card (with the Parallel port set to IRQ7, floppy and 1.2GB hard drive installed)
350W Seasonic 80 Plus Bronze PSU with ATX to AT converter (with -5v added)

Long version:

I can't get any 8bit soundcards (and some others) to work in this system! I don't think it's caused by a resource conflict because an SB Pro2 CT1600 works fine with the same IRQ and IO port settings. I can boot from the hard drive to DOS 6.22, I can use a Parallel to CF reader for external storage and everything works fine except that I get no sound in any games when using any 8bit cards. I've tried my CT1350B, MediaVision Thunderboard and an Aztech SoundGalaxy BXII and they all give me random buzzing and static. All are set to IRQ5 and address 220, just like the CT1600.

I thought maybe it was related to some of the cards requiring -5v (I'm using a modern ATX PSU with one of the adapters that adds -5v), but using an ISA tester card it shows -5v as being there and I can use my DMM on the -5v test points and it is showing about -4.85v. Last week when I first noticed the issue with the CT1350B I tried using an old AT PSU and had the same problem, so it really doesn't seem to be -5v related. Also it doesn't look like the -5v pin on the Thunderboard is connected to anything so that definitely rules that out for that card. I just tested the CT1350B in another system (also using a -5v adapter on an ATX PSU) and it works flawlessly with no setup required... CMS and FM both work.

I just tried a PAS16 in my 386 and the installer simply says that no Pro AudioSpectrum 16 is detected. Also tried the PAS Studio drivers and had the same problem. I know that the PAS16 does require -5v, but from what I gather it only affects the audio output. Not having -5v shouldn't disable the card completely... plus, as mentioned, I've already tested the -5v right at the ISA slot and it is there.

The only other thing I can tell that is different between the working and non working cards is that ALL of the ones that are not working use the OSC pin on the ISA connector. The SB Pro2 does not use this. I'm just about hitting the limits of my knowledge, but I guess allows a card to get its clock from the motherboard, rather than a clock on the card. I thought I'd found the problem when I saw that the solder joints on the legs of the 14.31818Mhz crystal on my board were looking a bit sad, so I reflowed them with my iron and some flux (they look perfect now)... and it still doesn't work. I still get the same low, growly, static noise. The volume of the noise is affected by the volume pot on the cards as well.

I'm at a loss. What would cause something like this? Is it likely a hardware fault? Where would I start to diagnose it? I do own an oscilloscope, but I don't really know how to use it. If that could help fix a clock related problem, I'll give it a shot.
Last edited by Ozzuneoj on 2019-1-17 @ 22:26, edited 4 times in total.
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Re: 386SX will not work with most sound cards...

Postby Jo22 » 2019-1-14 @ 04:38

Hm. Not sure either. You could try to replace that crystal oscillator by a socket and try another one.
I haven't tried yet, but if the the main oscillator on such a mainboard can be socket (like an 80Mhz type on a 386DX40),
it shouldn't hurt that much from an electric point of view.

If you have a short wave radio with a BFO knob (for SSB reception), you could also try to hear a signal on ~14MHz (beeeeep).
You can also test that out of cicuit. If you've got a classic 4,5v battery at hand (or a 9v battery), you are ready to go.
Just remember to add a few centimetres of wire to the out pin, so a nearby receiver can pick the signal up.

Edit: An oscilloscope is also fine. You need a 20Mhz or higher model (50MHz), I believe (my father has one and knows how to use it, I don't).
Also keep in mind that these TTL oscillators produce harmonics. A signal should also be visible on 28MHz and so on.
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Re: 386SX board will not work with most sound cards...

Postby Ozzuneoj » 2019-1-17 @ 04:36

Thanks for the tips Jo22!

I was going to start digging into this a bit further but decided to try to find another card that has the OSC pin connected to something. I have a CT1740\CT1730 with DSP 4.05 and it has the OSC pin connected. I don't know much about circuits, but I traced it out and the pin does lead through a couple resistors and into the main CT1746B chip, so I would imagine the clock provided by the motherboard is being used for at least something. However, the card does have its own 14.32Mhz crystal and it DOES connect to "master clock input" pin (24) on the YMF262-M. The result? FM music works without a hitch! I will report back shortly once I've tested a game with digital effects too.

EDIT: Just tried Flashback and Mixed Up Mother Goose VGA (for my daughter! :blush: ) and when configured properly I get FM music and "sound blaster" sound effects with the CT1740. Replacing the CT1740 with the CT1350B and doing the same tasks gives no sound... just a gross sounding static at high volumes. This is very confusing...

I'm at a loss here. Surely someone has seen something like this before.
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Re: 386SX board will not work with most sound cards...

Postby Ozzuneoj » 2019-1-17 @ 22:22

Just to be sure, I just tried an old AT power supply again, and I tested 3 different PAS16 card and I get the same results.

I can try to figure out the oscilloscope next (it is a Tektronix 2235 100Mhz model) to see if I can find any issues with the clock, but I'm not really sure how to go about that yet without just pulling the crystal from the board and test it out of circuit. If it tests okay there it could be a problem elsewhere in the clock circuit... or it could be totally unrelated. In the mean time, here are pictures of the cards I've tested so far. The four on the left do NOT work in this 386 board, the two on the right (CT1600 and CT1740) work fine. The three 8 bit cards produce no digital or FM sound (or CMS), and the PAS16 cannot be initialized by the installer (same with two other PAS16 variants I have).

0117191701 (1920x1440).jpg
0117191701a (1920x1440).jpg

0117191702 (2048x1536).jpg
0117191702a (2048x1536).jpg


Any insight at all could save me a ton of time trying to diagnose this.

Has anyone ever found a motherboard incompatibility with 8bit soundblaster compatible cards? It seems so odd since this is probably the kind of system that these cards would have been made for.

If I were to try a different BIOS that actually has some options, where could I find one that'd work with this odd board?
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