I found two places to measure but not sure I know what to expect. The offset is more than 50 mV at first then settles to nearly zero after a second or two. Then shortly thereafter the machine shuts itself off.
I can't see where to find the other outputs to check their offset. This unit is obviously not designed with repair in mind.
Each amplifier has a low Q choke in the output. I found two of these chokes and used them for test points but can't find the rest of them.
I'm about ready to throw in the towel. No matter how well these units might be designed electrically, no matter how carefully they are assembled and tested, no matter what quality components are used, I consider it a piece of junk if a reasonably competent technician can't work on it.
And there is no adequate technical description of the protection circuitry. I'm open to ideas but my frustration level is high.
I can't see where to find the other outputs to check their offset. This unit is obviously not designed with repair in mind.
Each amplifier has a low Q choke in the output. I found two of these chokes and used them for test points but can't find the rest of them.
I'm about ready to throw in the towel. No matter how well these units might be designed electrically, no matter how carefully they are assembled and tested, no matter what quality components are used, I consider it a piece of junk if a reasonably competent technician can't work on it.
And there is no adequate technical description of the protection circuitry. I'm open to ideas but my frustration level is high.
Okay Gajanan, I believe I have repaired it. Not knowing where to measure, I decided that it might be a major problem and so began to measure all the little test points for the bias. I figured the voltage wouldn't be the offset exactly but would at least be within a volt or so of it.
I measured a few and when I got to one in particular, it measured zero. I wiggled the little connector and suddenly the unit started working properly! Apparently it was a loose or corroded contact and now everything works. I didn't have to plug in the soldering iron or measure anything precisely or make any adjustments.
I appreciate your comments and without them I would have given up. Thanks!
I measured a few and when I got to one in particular, it measured zero. I wiggled the little connector and suddenly the unit started working properly! Apparently it was a loose or corroded contact and now everything works. I didn't have to plug in the soldering iron or measure anything precisely or make any adjustments.
I appreciate your comments and without them I would have given up. Thanks!
An update. I was happy with the repair and was replacing the cover when I realized the unit was getting very warm. There turns out to be a service bulletin, three pages long, that describes a procedure for just this problem. It requires removal of all the bias boards (I think) and replacing the interconnection cable with hard wiring, avoiding connectors. In addition, the same procedure is done for the fan.
This looks like a lot of work. I'm not sure this 10 year old unit is worth it. But at least I know where I stand with this.
This looks like a lot of work. I'm not sure this 10 year old unit is worth it. But at least I know where I stand with this.
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