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Post by mastertech on Mar 18, 2019 20:56:57 GMT -5
Well, this is what we know Figured out the hot heat sinks by realizing the trim pots are for Bias not DC offset. Well you are still assuming here. I do not know if those pots are actually for bias or just affecting it. I saw a - reading on your 1 meter reading where you said it might be reversed wires but you never confirmed that.With all output transistors removed as well as the amp board we still have DC. With amp board removed you still had DC? Where? I don't remember this.Put new DC blocking cap and still have DC may not be large enough caps. Remember this is old school class A. things were not well built back then, and limited components.So Only thing left in my view is the relay, or relay board . I really doubt this. But to verify just remove wire from cap that goes to relay and then test for DC on the cap where wire removed for DC., Might be from that board that its feeding back to the negative side of the DC blocking cap? Just trying to figure this out taking into consideration everything we removed and still have DC. Unless there is some continuity test I can do from the speaker outs to other places where there should not be any continuity. Might be picking up DC from there? bad diode leaking somewhere? Nashou |
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Post by mastertech on Mar 18, 2019 20:59:55 GMT -5
Is that the channel that has the soldered wires at the heatsink screw or the one that still has the device? That video was of the right side amp, the one I re capped . Both heat sinks have those two brown wire soldered or epoxy'd together . The other amp , the left one with those wires intact not broke free is also acting the same way but a bit more stable. I put those bundles wires back into the fastener and squeezed the crimp around them. so its like the other. But the contact is probably not as good as the one that was not broke free. Nashou I do not think those wires should be in those connectors on those heatsinks. They were most likely connected to a varistor and someone removed them and connected the wires. They were on the heatsink just for cooling. If that heat sink is grounded then you are maybe grounding out those wires and they should no be. |
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nashou
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Post by nashou on Mar 18, 2019 21:10:28 GMT -5
Well, this is what we know Figured out the hot heat sinks by realizing the trim pots are for Bias not DC offset. Well you are still assuming here. I do not know if those pots are actually for bias or just affecting it. I saw a - reading on your 1 meter reading where you said it might be reversed wires but you never confirmed that.With all output transistors removed as well as the amp board we still have DC. With amp board removed you still had DC? Where? I don't remember this. Yes on the one channel i was getting 17 volts Dc and the other channel had none. you said some amps have DC on the outputs and the two caps remove it. I think it was back on page 3 or 4 Put new DC blocking cap and still have DC may not be large enough caps. Remember this is old school class A. things were not well built back then, and limited components. Ok, gotcha So Only thing left in my view is the relay, or relay board . I really doubt this. But to verify just remove wire from cap that goes to relay and then test for DC on the cap where wire removed for DC. Ok, i'll give it a shot , Might be from that board that its feeding back to the negative side of the DC blocking cap? Just trying to figure this out taking into consideration everything we removed and still have DC. Unless there is some continuity test I can do from the speaker outs to other places where there should not be any continuity. Might be picking up DC from there? bad diode leaking somewhere? Nashou |
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Post by mastertech on Mar 18, 2019 21:10:38 GMT -5
You know, I found a schematic of a relay board system like you have and it does look like it is possible it could put some DC on that side of the cap. And it probably would affect both channels. So I would disconnect both caps wires to the relay board and test for DC. This way that relay board is removed from the circuit.
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nashou
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Post by nashou on Mar 18, 2019 21:12:28 GMT -5
You know, I found a schematic of a relay board system like you have and it does look like it is possible it could put some DC on that side of the cap. And it probably would affect both channels. So I would disconnect both caps wires to the relay board and test for DC. This way that relay board is removed from the circuit. So disconnect the wire going to the relay board from the cap. then test the now vacant leg of the cap for DC? Ok have to take amp to soldering station . be back soon |
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Post by mastertech on Mar 18, 2019 21:15:53 GMT -5
yes
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nashou
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Post by nashou on Mar 18, 2019 21:34:02 GMT -5
ok 30+ volts on leg of both caps, old and new. So thats not it either. Aslo on the emitter resistors, the - reading was because the probes were reversed. I also noticed some thing odd or maybe its normal. My Green DMM has a feature that will detect Live AC if you put DMM near it and two red lights glow if your close enough. well if I bring it close to chassis with power off it glows if I touch the chassis the red lights go away !! or if I power it up the red lights go away. never experienced that unless I got he DMM near the transformer or the AC cord. I made a video of part of that do you want to see that as well? Nashou |
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nashou
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Post by nashou on Mar 18, 2019 21:37:41 GMT -5
here is video
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Post by mastertech on Mar 18, 2019 21:45:03 GMT -5
So with nothing connected to the neg side of both those caps you now test 30VDC on each?
Is there any DC on the speaker connectors now?
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Post by nashou on Mar 18, 2019 21:50:41 GMT -5
So with nothing connected to the neg side of both those caps you now test 30VDC on each? Is there any DC on the speaker connectors now? Yes 30 volts. I'll check speaker outs Also I read you question in the post about those supposed heat sensing wires. So I just measured the voltage from each pin to GND and they have about 30 volts from each, and across them neg probe on one and pos probe on the other i get about 1.6 vdc . Just more info. I'll check speaker outs now ........... NO voltage on speaker outs. So relay board is not an issue. |
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Post by mastertech on Mar 18, 2019 22:03:09 GMT -5
Are there any other components under those caps connected to the neg side. We need more then just those caps for that DC.
Also can you get me some good pics of that relay board? I am missing something here. I need to see components on it. I am signing off for tonight . I will look at pics tomorrow.
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nashou
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Post by nashou on Mar 18, 2019 22:24:38 GMT -5
Are there any other components under those caps connected to the neg side. We need more then just those caps for that DC. Also can you get me some good pics of that relay board? I am missing something here. I need to see components on it. I am signing off for tonight . I will look at pics tomorrow. nothing connected to negative side except the relay board. Ok Mac have a good night and thanks. I work a double tomorrow so no action till about 7:30 or so. Athanasios |
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Post by nashou on Mar 18, 2019 22:52:36 GMT -5
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Post by mastertech on Mar 19, 2019 17:03:37 GMT -5
Still difficult for me to trace things out in these pics. Where does the black wire go? Those (2) 3 watt resistors, what are they connected to? In the pic the resistors hide the traces. How many wires in total connected to that board and which are which?
Maybe just take the time to value test all components and resolder any questionable joints. There is surely filtering going on on this board since you know it is receiving 29v but only small voltage at speaker connects. Those 3 watters may be tied to the audio signal lines and I am wondering if they are tied to gnd.
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nashou
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Post by nashou on Mar 19, 2019 19:03:15 GMT -5
Still difficult for me to trace things out in these pics. Where does the black wire go? Those (2) 3 watt resistors, what are they connected to? In the pic the resistors hide the traces. How many wires in total connected to that board and which are which? Maybe just take the time to value test all components and resolder any questionable joints. There is surely filtering going on on this board since you know it is receiving 29v but only small voltage at speaker connects. Those 3 watters may be tied to the audio signal lines and I am wondering if they are tied to gnd. ok let me try to get more info from that board . Its hard to get better pics because all the wires ran through a hole in the chassis to the caps and also to the speaker selector switch. The relay runs on 24 volts from the silk screen on the clear plastic. I'll test to see if the 3 watts are tied to GND. Would I test at chassis GND ? Let me test some things. Can I also re solder the caps back in, including the original one I replaced. Also is it safe to turn amp on with driver boards out or would it possible damage the outputs. Just got home. I hate these 13 hour days i have. |
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