I have a Sound Blaster 16 model CT2230 which has developed a problem playing back 16 bit audio. I bought the board on eBay a month ago and it was working ok until recently. FM music sounds ok, 8-bit audio sounds ok, and 16-bit audio sound ok if I use the low DMA channel, but if I try to play back 16-bit audio using the high DMA channel it is very scratchy like there is static in the background. I have a video here: https://www.youtube.com/watch?v=fWGTh-UlOnk. My normal settings are IRQ 5, low DMA 1, and high DMA 5, but I tried high DMA on 6 and 7 and get the same issue. I have the IRQ and both DMA channels reserved my PnP BIOS settings so I don't think it is a conflict. I have also run the system checks on Checkit 3.0 and it says my DMA controller is OK.
Sorry to necro this, but I finally got around to doing some more testing and I thought some folks might find this interesting. Some further diagnosis:
- Repeated from above, but this is an important diagnostic criteria, so I'll repeat it. The issue ONLY affects the 16-bit DMA channel, 16-bit audio over 8-bit DMA channel works fine.
- The sound card behaves the same on a AOpen AP5VM Socket 7 board as it did on the PVI-486SP3, so we can rule out system-specific conflicts.
- I found that slightly flexing the board while playing the sound sometimes improves the audio quality. At one point after flexing the problem went away for several minutes before coming back. This points to a bad trace or broken solder joint.
- I made a recording of the 16-bit testing sound from diagnose.exe using the 8-bit DMA channel, then using the 16-bit DMA channel while flexing the board. Then I fed the WAV to ChatGPT (5.6 Sol high effort) and had it analyze it. Based on this, it strongly suspects the SD13 line. Here's the ChatGPT transcript: https://chatgpt.com/share/6a7739ce-1b04-83ea- … 4d-3ec0de46be60
- I'll do some more probing of the board out of the system as ChatGPT suggested and I'll update again if I isolate the problem.
Taking ChatGPT's advice, I traced from the ISA fingers to the pins CT1747 chip.
The routing is pretty straightforward:
- The 8 data lines on the front of the board go to 8 vias immediately above the fingers.
- On the back of the board, there are 8 short horizontal traces to reverse the order of the lines which then immediately go back to the front of the board through another series of vias.
- On the front, the traces continue directly up to the chip on the front side via short vertical traces. The data lines are all along the bottom edge of the chip, I think DA13 is pin 12.
- There weren't any obvious scratches or corrosion on any of the traces.
- The resistance measures close to 0-1 ohm all the way from finger to pin on all the data lines.
- Flexing did not produce any obvious differences in resistance, although I had the probe pressed on the pin so it could be holding it down.
At this point I decided to try reflowing the vias and pins along the bottom of the chip. This appears to have fixed the problem. Unfortunately I was too aggressive with the heat and caused the PCB to blister under the traces and solder mask. Luckily the damage appears to be cosmetic only and the board is working normally now.
To be clear for those reading the transcript, I didn't intend to use 450C--I don't use my hot air station often and maybe I brushed the temp knob when I took it out of the cabinet. My brain isn't a native celsius speaker and I didn't pay close enough attention to the temp reading.
I think ChatGPT could well have been hallucinating about the specific bit that was bad when analyzing the audio. But I think it was right about it being some data bit in the upper byte and it pointed me in the right direction. I just wish I had been more careful with the temp control on my hot air station. Oh well, live and learn. The board seems to be stable for now at least during several hours of testing.
Sound Blaster 16 CT2230 – scratchy/noisy 16-bit audio, eventually fixed
I'm deleting my ChatGPT transcripts of the troubleshooting sessions, so I thought I'd summarize my steps for anyone runs into the same problem. If anyone objects to my posting of an AI-assisted troubleshooting session, consider that I did ask the humans on this forum for help first and nobody replied, so I turned to ChatGPT.
The card is a Sound Blaster 16 CT2230. It worked normally when I first bought it used, but after being used for a while it developed a problem where 16-bit digital audio sounded scratchy/static-filled, somewhat like a weak FM radio station.
8-bit digital audio and MIDI/FM audio sounded fine.
My normal configuration was:
1A220 I5 D1 H5
The interesting part was that if I configured the high and low DMA to use the same DMA channel, so that 16-bit playback was transferred using DMA1, the 16-bit audio sounded normal.
I was initially suspicious of a DMA conflict, but testing ruled that out.
Things I tested:
The card behaved the same way in multiple motherboards.
High DMA 5, 6 and 7 all produced the same noisy 16-bit audio.
DMA1 playback was clean.
I cleaned the ISA edge connector with contact cleaner. No change.
8-bit PCM remained clean.
FM/MIDI remained clean.
At that point it appeared that the fault was somewhere in the portion of the card used by native 16-bit ISA DMA transfers rather than in the DAC or analog audio circuitry.
While experimenting, I flexed the PCB slightly and the problem suddenly disappeared. That was a major clue that there was probably an intermittent connection somewhere on the card.
Unfortunately the fix didn't last, and the crackling came back.
I made some recordings of good DMA1 playback and bad DMA5 playback and attempted to determine whether a particular data bit was failing by comparing the audio. That analysis didn't produce a reliable result, so I don't think anything useful can be concluded from it.
Tracing the PCB
The eight upper ISA data lines on the 16-bit extension are very easy to follow on this board.
On the component side they run from the ISA fingers to a row of eight vias. On the back of the board there are eight short horizontal traces which reverse their order, then another row of vias brings them back to the component side. From there they run almost directly into the CT1747.
I checked continuity through these paths from the ISA fingers all the way to the CT1747 pins. They all measured approximately 0-1 ohm, comparable to the other traces.
I also tried flexing the PCB while measuring continuity and couldn't provoke an obvious open circuit. It's possible that pressing the meter probe against the chip pin was mechanically holding a marginal joint together, though.
There were no obvious scratches, corrosion, or broken traces visible under magnification.
Repair
Since flexing the PCB had affected the fault, I decided to reheat the CT1747 pins and the nearby vias in the data path with a hot-air station.
After doing that, the 16-bit DMA audio became clean again.
So at this point the most likely cause appears to have been an intermittent solder joint, via connection, or similar PCB interconnect problem around the CT1747/data bus area.
I unfortunately got too aggressive with the hot air and had the station set to 450 C. The board apparently outgassed from the heat and developed a small blister/delaminated-looking area under the solder mask on the back side.
Fortunately, the copper traces and vias appear intact, continuity is still good, and the card is currently working normally. The damage appears to be cosmetic/localized, so I'm going to leave it alone rather than risk making it worse.
Summary:
18-bit PCM: Good 2FM/MIDI: Good 316-bit via DMA1: Good 416-bit via DMA5: Bad 516-bit via DMA6: Bad 616-bit via DMA7: Bad 7Multiple PCs: Same problem 8Cleaning edge: No effect 9Flexing PCB: Changed/fixed problem temporarily 10Reheating CT1747 11pins/vias: Fixed problem
So if a CT2230 has noisy/crackly 16-bit PCM while 8-bit audio is fine, and the problem follows the card between systems, it may be worth checking for intermittent connections around the CT1747 and the upper ISA data-bus traces/vias before assuming the DAC or DSP itself has failed.