Lack of PCM can be bad DAC chip. Yamaha DB60XG (XR712) and the NEC OEM board (XR385) use a same family DAC+ADC chip and I have seen more than 3 cards where this chip has failed, produring no output or very distorted output.

FM detection errors are fully digital side issue, but since the OPL core is inside a chip where all else is handled in is difficult to single out exact issue. Perhaps there's a pin with a bad solder that makes intermittent contact. Sometimes the crystals fail too, the 14.31818MHz one provides clock for OPL3 section but without an oscilloscope there isn't too much to do.

You're not getting digital sound out of the CT1740 because it is currently configured for use with an ASP/CSP chip. Either add that, or throw jumpers on the IFSD and APSD shunts otherwise.

I have completely forgotten about those jumpers. I had a SB16 with them in the wrong place and it played no PCM until they were set correctly.

Cloudschatze wrote on 2024-10-23, 05:20:

You're not getting digital sound out of the CT1740 because it is currently configured for use with an ASP/CSP chip. Either add that, or throw jumpers on the IFSD and APSD shunts otherwise.

That did the trick! Thank you, can't believe I missed that. 😅

What confuses me though, is during testing I did get distorted audio output at one point. And I'm pretty sure I hadn't connected those jumpers, which makes me wonder how distorted output would be possible in that instance.

Tiido wrote on 2024-10-23, 05:07:

FM detection errors are fully digital side issue, but since the OPL core is inside a chip where all else is handled in is difficult to single out exact issue. Perhaps there's a pin with a bad solder that makes intermittent contact. Sometimes the crystals fail too, the 14.31818MHz one provides clock for OPL3 section but without an oscilloscope there isn't too much to do.

Yeah, with everything integrated into the CT1747 chip I figured this could be a challenge to diagnose.

I do have an oscilloscope, so I should at least check the crystal frequencies and see if they are outputting correctly.

I also found a CT2230 card in my bins which uses the same chip, so at the very least I have something I can test and probe for comparison.

Did some probing of the 14.3MHz crystal.

Initially I tested the working CT2230 Sound Blaster 16. This resulted in a clean ~14.3MHz signal at 5V.

Then I tested the non-working CT2290. The result was very different. The frequency was jumping around and the voltage was not anywhere near 5V.

Not sure if this is a problem with the crystal itself or possibly some other components. I'll have to test around for shorts and voltages to see what might be at fault.

I couldn't find any circuit diagrams online for these cards, so I'll have to figure it out as I go. At least the CT2230 appears to have a very similar circuit layout, which makes it easy to have something to compare with.

You have R11, R12 and the two light colored capacitors to check, but it is highly unlikely they're at fault. The crystals themselves are mechanical devices with a thin sheet of quartz in it and they can break from something like a drop. HCT04 nearby is the actual oscillator, but it is unlikely that it or the resistors + capacitors are bad. You can try swapping the crystals between the cards if you don't have a spare. Most motherboards and video cards have a 14.31818MHz crystal on them, and many other sounds cards do too.

Shponglefan wrote on 2024-10-22, 22:19:

I have two Sound Blaster 16 cards with different faults. The CT1740 fails produce PCM audio, while CT2290 fails to detect and ou […]
Show full quote

I have two Sound Blaster 16 cards with different faults. The CT1740 fails produce PCM audio, while CT2290 fails to detect and output FM synthesis.

CT1740

The attachment Sound Blaster 16 CT1740 - no PCM audio.jpg is no longer available

In testing the CT1740, I did get PCM (digital samples) to play once, but it was highly distorted and full of static. Otherwise it fails to produce digital audio sample playback. FM and MIDI playback works fine, however.

The attachment Sound Blaster 16 CT1740 - no PCM audio - capacitors.jpg is no longer available

My initial instinct is this might be a faulty capacitor issue. While there are no obvious leaking or bulging caps, the distorted and/or lack of audio mimics symptoms I've seen with some sound modules with bad caps. I've also read that the Wincap capacitors used are of generally poor quality.

Turns out the issue was missing jumpers on the IFSD and APSD pins. Added jumpers, and the problem is fixed!

CT2290

The attachment Sound Blaster 16 CT2290 - no FM.jpg is no longer available

The CC290 has inconsistent detection and output of FM synthesis. In games like Wolfenstein 3D or Arkanoid: Revenge of Doh, the card generally won't be detected. In games like Doom, it won't give any obvious errors, but just won't output any FM music.

Digital PCM and MIDI playback, on the other hand, work fine.

However, occasionally will detect and play back FM synthesis correctly. I haven't been able to pin down any specific steps or pattern in this and it seems to be somewhat random. Again, I'm wondering if it might be either bad caps or some other faulty component.

The card also had what appears to be some trace repair between the C50 and C51 capacitors. In examining the solder joints underneath, there is no obvious signs of capacitor replacements or other rework.

The attachment Sound Blaster 16 CT2290 - no FM - capacitors.jpg is no longer available

I've examined both cards under a microscope with no obvious damage or faulty components, other than the above mentioned trace repair. I also cleaned the ISA contacts with Deoxit.

These cards were tested on two motherboards, processors (Pentium MMX 233 and Pentium 100), and DOS installs. I also tested a CT1750 and CT2940 with the same setups, and those two sound cards work perfectly 100% of the time. I don't think the issue is related to either drivers or some hardware incompatibility.

Any suggestions on any possible areas to look at for faults?

For the CT1740, since you mentioned adding jumpers fixed the PCM issue, it might be worth checking the solder joints and connections on the CT2290 as well, just in case there's a loose connection causing the FM synthesis problems.

Anonymous Coward wrote on 2024-10-23, 19:03:

For the CT1740, since you mentioned adding jumpers fixed the PCM issue, it might be worth checking the solder joints and connections on the CT2290 as well, just in case there's a loose connection causing the FM synthesis problems.

I had checked pins on the CT1747 and a few other ICs, and everything seemed solid. Incidentally, it turns out the issue was the crystal as the card started working again after replacing it.

Did some more testing for shorts around the 14.3 MHz crystal. Not finding any other issues, I decided to just replace it with a new 14.31818 MHz one. That fixed the issue!

The card now gets correctly detected and plays back FM synthesis sounds/music.

I checked it with the oscilloscope and it now shows a steady ~14.3MHz and 5V.

Thank you to everyone for the advice! That's two more working Sound Blaster 16 cards than I had a day ago. 😁

Tiido wrote on 2024-10-23, 18:44:

You have R11, R12 and the two light colored capacitors to check, but it is highly unlikely they're at fault. The crystals themselves are mechanical devices with a thin sheet of quartz in it and they can break from something like a drop. HCT04 nearby is the actual oscillator, but it is unlikely that it or the resistors + capacitors are bad. You can try swapping the crystals between the cards if you don't have a spare. Most motherboards and video cards have a 14.31818MHz crystal on them, and many other sounds cards do too.

This was spot on, it was the crystal that was faulty. Fortunately I had a few spare 14.31818MHz crystals from the last time I ordered them, so it was a quick replacement that fixed the issue. Thank you! 😀

Anonymous Coward wrote on 2024-10-23, 19:03:

Shponglefan wrote on 2024-10-22, 22:19:

I have two Sound Blaster 16 cards with different faults. The CT1740 fails produce PCM audio, while CT2290 fails to detect and ou […]
Show full quote

I have two Sound Blaster 16 cards with different faults. The CT1740 fails produce PCM audio, while CT2290 fails to detect and output FM synthesis.

CT1740

The attachment Sound Blaster 16 CT1740 - no PCM audio.jpg is no longer available

In testing the CT1740, I did get PCM (digital samples) to play once, but it was highly distorted and full of static. Otherwise it fails to produce digital audio sample playback. FM and MIDI playback works fine, however.

The attachment Sound Blaster 16 CT1740 - no PCM audio - capacitors.jpg is no longer available

My initial instinct is this might be a faulty capacitor issue. While there are no obvious leaking or bulging caps, the distorted and/or lack of audio mimics symptoms I've seen with some sound modules with bad caps. I've also read that the Wincap capacitors used are of generally poor quality.

Turns out the issue was missing jumpers on the IFSD and APSD pins. Added jumpers, and the problem is fixed!

CT2290

The attachment Sound Blaster 16 CT2290 - no FM.jpg is no longer available

The CC290 has inconsistent detection and output of FM synthesis. In games like Wolfenstein 3D or Arkanoid: Revenge of Doh, the card generally won't be detected. In games like Doom, it won't give any obvious errors, but just won't output any FM music.

Digital PCM and MIDI playback, on the other hand, work fine.

However, occasionally will detect and play back FM synthesis correctly. I haven't been able to pin down any specific steps or pattern in this and it seems to be somewhat random. Again, I'm wondering if it might be either bad caps or some other faulty component.

The card also had what appears to be some trace repair between the C50 and C51 capacitors. In examining the solder joints underneath, there is no obvious signs of capacitor replacements or other rework.

The attachment Sound Blaster 16 CT2290 - no FM - capacitors.jpg is no longer available

I've examined both cards under a microscope with no obvious damage or faulty components, other than the above mentioned trace repair. I also cleaned the ISA contacts with Deoxit.

These cards were tested on two motherboards, processors (Pentium MMX 233 and Pentium 100), and DOS installs. I also tested a CT1750 and CT2940 with the same setups, and those two sound cards work perfectly 100% of the time. I don't think the issue is related to either drivers or some hardware incompatibility.

Any suggestions on any possible areas to look at for faults?

For the CT1740, since you mentioned adding jumpers fixed the PCM issue, it might be worth checking the solder joints and connections on the CT2290 as well, just in case there's a loose connection causing the FM synthesis problems.

There must be a problem with the site, because I definitely did not write that reply.

Shponglefan wrote on 2024-10-24, 00:13:

This was spot on, it was the crystal that was faulty. Fortunately I had a few spare 14.31818MHz crystals from the last time I ordered them, so it was a quick replacement that fixed the issue. Thank you! 😀

Excellent, enjoy the cards ~
Perhaps socket the MCU for adding bug fixed one in there, this is something I plan to do to all my SB16 cards.

Tiido wrote on 2024-10-24, 05:08:

Excellent, enjoy the cards ~
Perhaps socket the MCU for adding bug fixed one in there, this is something I plan to do to all my SB16 cards.

What's the MCU? Are you talking about the DSP chip (CT1741)?

Shponglefan wrote on 2024-10-24, 23:17:

What's the MCU? Are you talking about the DSP chip (CT1741)?

Yeah, the "DSP" is an Intel 8051 microcontroller.

I bought a CT1740 on eBay a while ago, but it’s missing the C48 capacitor. Can someone tell me the value of that cap?
Thanks!

1uf 50v