I recently got from a friend an older Crown com-tech 210 amplifier that was destined for the junkyard. As my name suggests I am not much of a solid state guy so any help is much appreciated.
The unit powers up with no protection going active and has output to the speakers but treble and mids are EXTREMELY high with almost no bass response. When input is increased output volume increases too but it seems around 1/4 output power the amp falls on its face and distorts on any peak with the front panel distortion indicators coming on.
This issue is common to both channels when in stereo mode leading me to hypothesize a possible power supply problem.
Any ideas or where I should start looking? I have several DVM, oscilloscope, variac, 0-50 volt bench supply and of course an 8 ohm 100w dummy load at my disposal.
The unit powers up with no protection going active and has output to the speakers but treble and mids are EXTREMELY high with almost no bass response. When input is increased output volume increases too but it seems around 1/4 output power the amp falls on its face and distorts on any peak with the front panel distortion indicators coming on.
This issue is common to both channels when in stereo mode leading me to hypothesize a possible power supply problem.
Any ideas or where I should start looking? I have several DVM, oscilloscope, variac, 0-50 volt bench supply and of course an 8 ohm 100w dummy load at my disposal.
Could be that, could be just dried up rail or op amp rail supply caps.
Energize with a transistor radio with the 8 ohm load on it. Pick up an analog VOM somewhere unless your DVM is the RMS variety. Turn source up to starts sounding bad, ie clipping. Measure AC voltage out each channel. 100 watts/channel would be 28 vac. If using scope multiply peak to peak by 0.7.
If a lot less, your rail caps are dried up. Op amp rail caps can cause low output too, but usually the big ones go first.
I use ones rated more than 3000 hours service life so I don't have to do this again every 8 years or so. Newark & digikey have the hours service life available in the selector table.
Schematic may be available on eserviceinfo.com or other internet sources.
Energize with a transistor radio with the 8 ohm load on it. Pick up an analog VOM somewhere unless your DVM is the RMS variety. Turn source up to starts sounding bad, ie clipping. Measure AC voltage out each channel. 100 watts/channel would be 28 vac. If using scope multiply peak to peak by 0.7.
If a lot less, your rail caps are dried up. Op amp rail caps can cause low output too, but usually the big ones go first.
I use ones rated more than 3000 hours service life so I don't have to do this again every 8 years or so. Newark & digikey have the hours service life available in the selector table.
Schematic may be available on eserviceinfo.com or other internet sources.
Ok, some things came up and I wasn't able to touch the amp for a couple weeks. Today I opened it up and was going to so some test measurements of rail voltage, etc.
I hooked up speakers, gave it an input signal and lo and behold it's working perfectly. I did not change anything at all from when it was sitting in the same spot on my bench acting weird.
The only thing I did was there is an input card on the back that has about a 14 pin connector on the back of it. I removed and re seated this card.
The wife was at work so I let it rock. It sat there and happily ran at near full power for several hours without any objection.
I'm baffled. Could it have been this input card all along?
Btw I did check out internals and it all looks good. Nothing burnt or leaking. Rails for both channels sit at 68V at idle and sag to about 60V at full power so ok there.
Just weird it's all of a sudden working. Russian hackers? Garden gnomes fixed it? Electromagnetic vortecies? Unicorns?
I hooked up speakers, gave it an input signal and lo and behold it's working perfectly. I did not change anything at all from when it was sitting in the same spot on my bench acting weird.
The only thing I did was there is an input card on the back that has about a 14 pin connector on the back of it. I removed and re seated this card.
The wife was at work so I let it rock. It sat there and happily ran at near full power for several hours without any objection.
I'm baffled. Could it have been this input card all along?
Btw I did check out internals and it all looks good. Nothing burnt or leaking. Rails for both channels sit at 68V at idle and sag to about 60V at full power so ok there.
Just weird it's all of a sudden working. Russian hackers? Garden gnomes fixed it? Electromagnetic vortecies? Unicorns?
> Russian hackers?
Maybe.
> I removed and re seated this card.
My much older Crown tape deck needed its cards pulled and reseated frequently.
Tarnish never sleeps.
Maybe.
> I removed and re seated this card.
My much older Crown tape deck needed its cards pulled and reseated frequently.
Tarnish never sleeps.
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