VOGONS

Yamaha DB50XG - can hear faint music only if external speakers turned to 11

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First post, by Space Ace

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Hi,

I have an old Yamaha DB50XG that failed some time ago. Turning up the MIDI volume, speakers/amplifier to the max I could hear a faint few crackles when I attempted to play a midi file/game. Dead silent except for hiss otherwise but starting up a midi file or game I could hear faint crackles as if something was trying to play. A few weeks ago I had a look under a microscope and noticed that the NEC D63200 DAC seemed to have failed with a small crater near pin 11 (L Audio out) I looked at a few threads on Vogons and one user with a failed DB50XG replaced the D63200 DAC as well as the NEC 4570 Opamps (no updates after so not sure if this ever worked) Anyway I went ahead and replaced the chips. So there is progress, the audio is still very, very low, but if I turn the amp to the max I can now hear faint midi music playing. Everything else on the card looks to be fine, caps and resistors seem to check out. No loose legs on any IC. I thought perhaps the op-amps were faulty so changed back to the original ones and audio volume still the same. I checked with a multimeter and get -5 and +5 at the respective pins for each op-amp so the voltage regulators seem to work OK?

I also checked the soundcard (I only have one) an OEM ESS1868 and have also enabled and set max volumes with ESSVOL. Not sure what to try next. I thought the -5/+5 voltage might be low but appear to be in spec for the Op-amps and the voltage from the Wave blaster pins are correct at +5, +12, -12.

The user with the dead DB50XG also replaced the 74HC14A Hex Schmitt Trigger Inverter, I haven't yet and not sure if its worth it. Finally, I couldn't test some of the tantalum caps in circuit with my multimeter (no reading) but desoldering two, both returned the correct values, I didn't want to desolder all the rest to test so assume they're OK (the ones I cant get a reading from) there were a few traces at the back of the board that looked suspect and I thought I had it nailed but alas that's not the issue.

Any ideas?

Thanks,

Reply 1 of 7, by Tiido

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This may have been a case of bad connection on the WB header, off by one connection can result in catastrophic failure and the crater on the DAC chip suggests that may have happened.

Since there is some sound, the DAC is probably fine now but there are likely bad opamp(s) too, in addition you need to check if the tantalum capacitors C24+25, 36+37, 63+64 have shorted.

Lacking oscilloscope, you can debug with a 3.5mm audio cable connected to sound card's line-in. By touching with the plug tip some areas in the signal path you can hear where exactly sound disappears.

T-04YBSC, a new YMF71x based sound card & Official VOGONS thread about it
Newly made 4MB 60ns 30pin SIMMs ~
mida sa loed ? nagunii aru ei saa 😜

Reply 2 of 7, by Space Ace

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Thanks Tiido, when searched the issue last week I came across one of your comments about repairing these.

Yes wrong install is exactly what happened in 2016 when I visited SAfrica and put the old PC back together and decided to take it and attempt to fix it with a recent visit. I soldered in new opamps when I replaced the D63200 and then replaced the new ones back to the original ones when the audio volume didn't return to normal. Do you think both the new and the old could possibly be faulty? C36 and C37 have 4.8µF readings (tested in circuit) I will have to lift a leg for C24+C25, C63,C64 but can see they're not shorted with continuity test on the multimeter.

Would replacing 74HC14A IC be of any use? I tested again yesterday and can clearly hear Duke3d Grabbag play in the sound config so there is hope this card can be fixed. Thank you, I might try that 3.5mm audio cable technique but concerned I will short out something else whilst poking around with the cable.

Reply 3 of 7, by Tiido

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The logic chip is only address decoder for the two sample ROMs and reset signal handling, and if there's a fault there you get garbled digital noises but since you hear proper music this part definitely works.

Ok, the capacitors are likely fine then. Are both channels are equally quiet or is there an imbalance ? Are voltages over C70 and C74 at 5V ? It is unlikely that the new opamps got damaged unless they were soldered on the wrong way around but in that case they get really hot and so will the voltage regulators. Is anything hot in the analog area ?

You do need to be careful with the 3.5mm method, especially around the + and - voltage pins on the opamps. Shorting one of those with output (+ and out are next to each other) can kill the channel on that particular opamp.

T-04YBSC, a new YMF71x based sound card & Official VOGONS thread about it
Newly made 4MB 60ns 30pin SIMMs ~
mida sa loed ? nagunii aru ei saa 😜

Reply 4 of 7, by Space Ace

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I've just checked and C74 is -4.9v and C70 is 5v. I noticed there is almost no voltage at C63 and C64 (0.09v) - that doesn't look right. C36 and C37 only 1.65v - that seems low?
C71 is -10.8v and C67 is 11.65v

I've ordered a IDC Extension jumper cable so I can better test the module away from the soundcard. At the moment I have carefully balance and poke at precarious angles and will for sure short something if I continue. Temperature wise nothing is warm above ambient, the only IC that gets warm is XQo36AOO and only about 40 degrees at most?

Reply 5 of 7, by Space Ace

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Space Ace wrote on Today, 11:30:

I've just checked and C74 is -4.9v and C70 is 5v. I noticed there is almost no voltage at C63 and C64 (0.09v) - that doesn't look right. C36 and C37 only 1.65v - that seems low?
C71 is -10.8v and C67 is 11.65v

I've ordered a IDC Extension jumper cable so I can better test the module away from the soundcard. At the moment I have carefully balance and poke at precarious angles and will for sure short something if I continue. Temperature wise nothing is warm above ambient, the only IC that gets warm is XQo36AOO and only about 40 degrees at most?

Sorry should have said, both channels are equally low in volume

Reply 6 of 7, by Space Ace

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SOLVED!! - it was the ESS Audiodrive soundcard.

I ordered replacement ESS Audio drive and the thing immediately works with the exact same ESSVOL settings. My room is now filled with lovely DB50XG Midi music haha and just to annoy my neighbour for 4 minutes I will now play Theme Hospital Candy Floss on full volume 😀

Sorry for wasting your time Tiido, for sure the D63200 was fried and so glad I noticed the audio now playing with maximum amplification otherwise it would have gone on Ebay as faulty.

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