Do you happen to have a multimeter with frequency counter (Hz) mode? They're cheap, but do check the max value which can be measured. Also one can't check how 'clean' the sinewave is.

PD2JK wrote on 2026-02-10, 18:23:

Do you happen to have a multimeter with frequency counter (Hz) mode? They're cheap, but do check the max value which can be measured. Also one can't check how 'clean' the sinewave is.

My multimeter has the function, but it only goes up to 10Mhz so that wouldn't be very useful unfortunately

I replaced the 24mhz oscillator and the card sprang back to life. Previously DIAGNOSE.EXE didn't pick it up at all, now the configuration went through fine and all sound tests worked. DOOM now has all sound effects, along with the music that already worked previously. So this oscillator seems to be a fairly common issue with these cards

The part for repair is like 50 cents each on aliexpress, so very cheap. Just search for "24mhz crystal HC-49U" to find the ones that have the same physical dimensions as the original. You also need a piece of solid core wire to ground the body of the crystal (same as was done in the factory)

Good to hear it's working, great job.

PD2JK wrote on 2026-02-10, 18:23:

Also one can't check how 'clean' the sinewave is.

With an oscilloscope that can do FFT you can, and if the freq is within audio band when with a recording of that sinewave in decent audio editor. FFT will reveal any extra harmonics and gives a perfect measure of how clean/dirty that sinewave is.

Feallan wrote on 2026-02-10, 21:31:

PD2JK wrote on 2026-02-10, 18:23:

Do you happen to have a multimeter with frequency counter (Hz) mode? They're cheap, but do check the max value which can be measured. Also one can't check how 'clean' the sinewave is.

My multimeter has the function, but it only goes up to 10Mhz so that wouldn't be very useful unfortunately

I have same problem with a SB16 CT2800, card not detected in DOS or windows, no PCM sound but FM works.

Just wondering if I used a multimeter with frequency counter (mine goes to 1mhz max ) wouldn't this work as q quick test just to tell if the oscillator is dead or not. Such as it will show 0 count if dead or 1mhz if working?

Multimeter can help in the sense that if you read a voltage on a 50% duty cycle clock, it should give you around 2.5V reading. If the clock is stopped it'll give 0 or 5V, assuming measurement with the multimeter doesn't stop the oscillator circuit from excess capacitance etc.

Riikcakirds wrote on 2026-02-25, 17:03:

Feallan wrote on 2026-02-10, 21:31:

PD2JK wrote on 2026-02-10, 18:23:

Do you happen to have a multimeter with frequency counter (Hz) mode? They're cheap, but do check the max value which can be measured. Also one can't check how 'clean' the sinewave is.

My multimeter has the function, but it only goes up to 10Mhz so that wouldn't be very useful unfortunately

I have same problem with a SB16 CT2800, card not detected in DOS or windows, no PCM sound but FM works.

Just wondering if I used a multimeter with frequency counter (mine goes to 1mhz max ) wouldn't this work as q quick test just to tell if the oscillator is dead or not. Such as it will show 0 count if dead or 1mhz if working?

Instead of poking around a live system with a multimeter I decided to just replace this very cheap part, that has a seemingly high failure rate. I recommend this approach, but FYI the original crystal is not the easiest thing do desolder with just cheapo solder sucker and wick - for 2 out of 4 points, most of the heat quickly goes into the ground plane. I recommend cutting all the legs with pliers to give better access to the solder sucker

Feallan wrote on 2026-02-25, 22:34:

Riikcakirds wrote on 2026-02-25, 17:03:

Feallan wrote on 2026-02-10, 21:31:

My multimeter has the function, but it only goes up to 10Mhz so that wouldn't be very useful unfortunately

I have same problem with a SB16 CT2800, card not detected in DOS or windows, no PCM sound but FM works.

Just wondering if I used a multimeter with frequency counter (mine goes to 1mhz max ) wouldn't this work as q quick test just to tell if the oscillator is dead or not. Such as it will show 0 count if dead or 1mhz if working?

Instead of poking around a live system with a multimeter I decided to just replace this very cheap part, that has a seemingly high failure rate. I recommend this approach, but FYI the original crystal is not the easiest thing do desolder with just cheapo solder sucker and wick - for 2 out of 4 points, most of the heat quickly goes into the ground plane. I recommend cutting all the legs with pliers to give better access to the solder sucker

It was the crystal, and replacing it fixed the card. I ended up like you said cutting the legs to remove the old crystal but i didn't then desolder them as the two holes looked pretty worn, don't know why. So i ended up soldering the legs of the new crystal to the cut legs of the old crystal. Everything is working.
To test the card I disabled all non-used inputs like mic, cd, line-in etc in the mixer and testing at ull volume with headphones and, it surprised me how low noise this card is (ct2800).

Nice, glad my information was of some help. The oscillator holes on my card didn't look particularly good, but the solder attached well enough. The biggest problem was that they made them too wide for the thin legs of the oscillator and the solder could very easily travel to the other side

My CT2230 has a lot of noise, not sure what's the "normal" noise level on this card as I didn't have any ISA Sound blaster until recently

Feallan wrote on Yesterday, 22:15:

My CT2230 has a lot of noise, not sure what's the "normal" noise level on this card as I didn't have any ISA Sound blaster until recently

I thought my CT1770 was "very noisy" until I saw the output gain multiplier in mixerset.exe defaulted to 2x. When I set it to 1x and maxed out the sliders to compensate, the card was just regular "noisy".