The Dude Posted August 13, 2014 Author Share Posted August 13, 2014 OK some testing done last night. I pulled both output cards, and tested the power supply voltages which where at 35, and -35 so those are good. However when I plugged the problem board the voltages dropped is this normal(which I don't see how it is do to the schematic showing these voltages with the cards in) or is this do to the short somewhere in the board. Now a quick note on this board, these boards plug into a socket. When I first plugged it in, it appeared the bulb was dimming down, but then I kind of wiggled it. Now it may be a fluke but the bulb brightened up. So is it possible it could just be a bad connection from the socket to the board. When I was checking voltages at the spot indicated nothing seemed right except some 80 and 90 volts that were present. Dirty contacts that are capacitvely coupling instead of making good contact MIGHT be contributing to your problems. Dirty volume pots also What about by passing the volume pots and even mono/stereo switch to see if some problems go away. Quote Link to comment Share on other sites More sharing options...
babadono Posted August 13, 2014 Share Posted August 13, 2014 (edited) OK some testing done last night. I pulled both output cards, and tested the power supply voltages which where at 35, and -35 so those are good. However when I plugged the problem board the voltages dropped is this normal(which I don't see how it is do to the schematic showing these voltages with the cards in) or is this do to the short somewhere in the board. Now a quick note on this board, these boards plug into a socket. When I first plugged it in, it appeared the bulb was dimming down, but then I kind of wiggled it. Now it may be a fluke but the bulb brightened up. So is it possible it could just be a bad connection from the socket to the board. When I was checking voltages at the spot indicated nothing seemed right except some 80 and 90 volts that were present. Dirty contacts that are capacitvely coupling instead of making good contact MIGHT be contributing to your problems. Dirty volume pots also What about by passing the volume pots and even mono/stereo switch to see if some problems go away. OK but depending on how you 'bypass' you will have full volume or no volume Edited August 13, 2014 by babadono Quote Link to comment Share on other sites More sharing options...
babadono Posted August 13, 2014 Share Posted August 13, 2014 So is it possible it could just be a bad connection from the socket to the board. Heck yes it is possible. Quote Link to comment Share on other sites More sharing options...
babadono Posted August 13, 2014 Share Posted August 13, 2014 So with the boards unplugged the + and -35 volts come up, good. This means the power output transistors are not shorted, good. Can you do an ohm check on the boards? +35 and -35 to ground? to each other? The cards plug into connectors, what are the connector hooked to? I mean are they soldered into another board or do they have wires soldered to them directly? If it is wires something could be touching when you insert the cards. Quote Link to comment Share on other sites More sharing options...
The Dude Posted August 13, 2014 Author Share Posted August 13, 2014 OK some testing done last night. I pulled both output cards, and tested the power supply voltages which where at 35, and -35 so those are good. However when I plugged the problem board the voltages dropped is this normal(which I don't see how it is do to the schematic showing these voltages with the cards in) or is this do to the short somewhere in the board. Now a quick note on this board, these boards plug into a socket. When I first plugged it in, it appeared the bulb was dimming down, but then I kind of wiggled it. Now it may be a fluke but the bulb brightened up. So is it possible it could just be a bad connection from the socket to the board. When I was checking voltages at the spot indicated nothing seemed right except some 80 and 90 volts that were present. Dirty contacts that are capacitvely coupling instead of making good contact MIGHT be contributing to your problems. Dirty volume pots also What about by passing the volume pots and even mono/stereo switch to see if some problems go away. OK but depending on how you 'bypass' you will have full volume or no volumeWhen testing it says to have the volume knobs all the ccw. Which would be volume the way up. Quote Link to comment Share on other sites More sharing options...
The Dude Posted August 13, 2014 Author Share Posted August 13, 2014 Here some picks of the connector. First on is of the bottom and second one is of the top third will be of the card. Quote Link to comment Share on other sites More sharing options...
babadono Posted August 13, 2014 Share Posted August 13, 2014 When testing it says to have the volume knobs all the ccw. Which would be volume the way up. CCW would be all the way DOWN, IOW grounding the input to the amp. Quote Link to comment Share on other sites More sharing options...
The Dude Posted August 13, 2014 Author Share Posted August 13, 2014 When testing it says to have the volume knobs all the ccw. Which would be volume the way up. CCW would be all the way DOWN, IOW grounding the input to the amp. OH yea that would be right, guess I was thinking back words, sorry about that. Quote Link to comment Share on other sites More sharing options...
babadono Posted August 13, 2014 Share Posted August 13, 2014 So the connector contact at pin C looks a little deformed but probably no big deal, pin D looks like it has some of the insulator scraped down at the bottom. Any idea how that happened? Try to clean it out. The wiring on the bottom looks OK so long as the brown wire insulation is intact as it goes over the red and orange wires. Quote Link to comment Share on other sites More sharing options...
The Dude Posted August 14, 2014 Author Share Posted August 14, 2014 (edited) pin D looks like it has some of the insulator scraped down at the bottom I am trying to see what you are talking about by the pictures, I am heading to the garage now to check. Looking at the schematic c is 3 which is 90 volts from the power supply, d is not used. There are compete set of collector/emitter voltages on the board. You should test each of them I was thinking of comparing the voltages to the other board as well. But it will be tough as its hard to get in there. Edited August 14, 2014 by duder1982 Quote Link to comment Share on other sites More sharing options...
babadono Posted August 14, 2014 Share Posted August 14, 2014 yeah I see now by the wiring on the bottom pin D doesn't do anything. My bad. But still on the contact side the plastic looks scraped or deformed by pin D. Maybe its just the picture? On my monitor? I leave it to your judgement after all you're there, I'm not. So this is the connector of the channel of the amp giving you the problem. The 2 cards are identical if I'm not mistaken. Do both give you the problem in this socket? I mean have you tried swapping the cards? If you posted you already tried that I missed it, sorry. Quote Link to comment Share on other sites More sharing options...
The Dude Posted August 14, 2014 Author Share Posted August 14, 2014 add a "tail" to each important test point Should these be everywhere a voltage is listed. There seems to be a lot of .6 and .05 volts on the schematic particularly after transistors, are these just as important. Quote Link to comment Share on other sites More sharing options...
The Dude Posted August 15, 2014 Author Share Posted August 15, 2014 OK I didn't have anything to label each test point. What I did do is compare the good board to the bad board voltages. Where I had 35 volts on the good, I had 3.5 volts on the bad, same with the 90 volts on the good, I had 9 volts on the bad. So I started where I left off on replacing the resistors. My voltages started to rise, so there must have been some bad resistors(like mentioned), that was causing the draw or voltage drop. I got to the one of the last ones, and the light came back on and voltages dropped again. Which that one should be 22 ohms but tested a little over 25 ohms. I think if I get time this weekend I will try to pull the socket and tighten up the connections. Maybe I am getting and intermittent problem. As again I have 3.5 volts where I should have 35 and 9 volts where I should have 90. Quote Link to comment Share on other sites More sharing options...
babadono Posted August 15, 2014 Share Posted August 15, 2014 Sounds like you have a shorted or partially shorted transistor on that one board. Can you check them? Or just cut to the chase and replace all 7 of them. I don't like just replacing everything but sometimes to save time that's what gets it done. BTW is it the board with the "odd" numbered parts or "even". Quote Link to comment Share on other sites More sharing options...
The Dude Posted August 15, 2014 Author Share Posted August 15, 2014 Or just cut to the chase and replace all 7 of them I all ready replaced 3 out of 7. BTW is it the board with the "odd" numbered parts or "even" I didn't know there was one or the other. Quote Link to comment Share on other sites More sharing options...
babadono Posted August 19, 2014 Share Posted August 19, 2014 Have you checked the others? Quote Link to comment Share on other sites More sharing options...
The Dude Posted August 19, 2014 Author Share Posted August 19, 2014 No I haven't had time, and may not until after this weekend. Quote Link to comment Share on other sites More sharing options...
babadono Posted August 19, 2014 Share Posted August 19, 2014 I also noticed there are 2 electrolytic capacitors on the board. These can deteriorate with time/age. Quote Link to comment Share on other sites More sharing options...
The Dude Posted August 19, 2014 Author Share Posted August 19, 2014 I also noticed there are 2 electrolytic capacitors on the board. These can deteriorate with time/age. Those wear replaced right away. Quote Link to comment Share on other sites More sharing options...
The Dude Posted August 29, 2014 Author Share Posted August 29, 2014 Sorry I haven't been on this, I have been extremely busy and now just too tired. I will hopefully be up to it after this weekend. Quote Link to comment Share on other sites More sharing options...
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