You need to find out why you have no voltage driving the gate of the jfets low. The secondary winding's negative pulses pass through the series connected diode/resistor. One charges the cap. The other resistor/diode pair drives the gate of the jfet (near the regulator) low which turns it off. This allows the cap to charge toward the negative rail. The Jfet could be shorted. If you read zero ohms across it (out of the board, it's defective. If you read ~30-40 ohms between the drain and source when it's out of the board, it's likely OK. Current will flow both ways so they will read the same no matter which lead you have on the drain/source.
If you pull the muting jfets, you can confirm that the problem is indeed in the muting circuit (there will be no muting with them removed). I've seen them short but that caused the signal to remain muted no matter how long it remained on.
The disc capacitors are likely OK but you can't rule out anything.
Do you have a 'scope?
If you pull the muting jfets, you can confirm that the problem is indeed in the muting circuit (there will be no muting with them removed). I've seen them short but that caused the signal to remain muted no matter how long it remained on.
The disc capacitors are likely OK but you can't rule out anything.
Do you have a 'scope?
i just want to stop and say thanks for taking the time to help me out with this...
im going to pull the jfets tonight and see what happens, checked all the diodes and all are good.
could you tell me how to check if caps are good? i want to check out the disc shaped caps along with the mylars, but dont want to pull them if not necessary...a couple of disc are darkly discolored around the edges.
another weird thing, after i checked the jfets, the volume doesnt increase after 10 minutes anymore, the output stays low.
whats the purpose of this muting circuit? you said: "there will be no muting with them removed"......what will happen???
my hammer is starting to look awfully good .... 
no scope, got some listerine though
almost forgot, do you know an equivalent replacement for the 2n5639 just incase i cant find the same number...?
im going to pull the jfets tonight and see what happens, checked all the diodes and all are good.
could you tell me how to check if caps are good? i want to check out the disc shaped caps along with the mylars, but dont want to pull them if not necessary...a couple of disc are darkly discolored around the edges.
another weird thing, after i checked the jfets, the volume doesnt increase after 10 minutes anymore, the output stays low.
whats the purpose of this muting circuit? you said: "there will be no muting with them removed"......what will happen???
my hammer is starting to look awfully good .... no scope, got some listerine though
almost forgot, do you know an equivalent replacement for the 2n5639 just incase i cant find the same number...?
The muting transistors are used to prevent any turn on/off pops from getting to the amplifier circuit. If you remove the muting transistors, the audio will not be clamped as the amplifier turns on/off. If something in the preamp section of the amp or something in your signal line pops as it powers up, you'll hear it.
Did you replace the transistors properly? Most all PC boards use the square pad as pin 1. I think there must have been a mistake on this board. For the Jfets in this amp, pin 3 goes to the square pad.
For their use in this amp, in this part of the circuit, as long as the caps are not leaking/shorted, they should be OK. If you set your meter to diode check and touch the leads across the cap, the meter reading will change for a short period of time. For small caps (100uf or less), it will return to OL within a second or so. If you get a cap that gives a constant voltage reading on diode check, it's leaky and needs to be replaced. Although there is little chance that it will make a difference on diode check, don't touch the leads during the test. Use alligator clip-leads or probes with clips.
Was there any corrosion under the mute delay cap?
If you need to replace the muting transistors, try to find the originals. I've never looked for a sub and I don't deal with jfets often so I don't know of one.
Did you replace the transistors properly? Most all PC boards use the square pad as pin 1. I think there must have been a mistake on this board. For the Jfets in this amp, pin 3 goes to the square pad.
For their use in this amp, in this part of the circuit, as long as the caps are not leaking/shorted, they should be OK. If you set your meter to diode check and touch the leads across the cap, the meter reading will change for a short period of time. For small caps (100uf or less), it will return to OL within a second or so. If you get a cap that gives a constant voltage reading on diode check, it's leaky and needs to be replaced. Although there is little chance that it will make a difference on diode check, don't touch the leads during the test. Use alligator clip-leads or probes with clips.
Was there any corrosion under the mute delay cap?
If you need to replace the muting transistors, try to find the originals. I've never looked for a sub and I don't deal with jfets often so I don't know of one.
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