700B blew one Right channel 5A supply fuse

[laatsch55]

No Gary that's fine, just check on each side of the 10 ohm so we see where were at..

 

[laatsch55]

Disconnecting the D9,D10 diodes disable the protection circuit, we'll leave it unhooked for awhile yet...

 

[62vauxhall]

No Gary that's fine, just check on each side of the 10 ohm so we see where were at..

The lesser digits vary on both sides but;

Left channel.... -3.2V DC
Right channel quickly climbed to ....-121V DC

 

[laatsch55]

No decimals in the 121 minus voltage??

 

[62vauxhall]

No decimals in the 121 minus voltage??

Sorry - not paying attention.

Right channel....-3.9 volts DC
Left channel ....-122.6 millivolts DC

 

[laatsch55]

Try adjusting bias on the left channel, see if it has an effect...

 

[NavLinear]

Nav, if you've got some advise, let's hear it....

I'd put a 20 to 50 ohm 5 or 10 watt resistor in series with the alligator clips to bleed down the reservoir caps.

 

[laatsch55]

Thanks Navo, I always forget the obvious...

 

[62vauxhall]

Try adjusting bias on the left channel, see if it has an effect...

The Left side bias control was nearly full anti-clockwise. Taking it to full anti-clockwise reduced the voltage to about about 1.4 Volts (not minus) but the lesser digits were not stable - kept climbing.

Turning the control clockwise raised the voltage. I stopped at about 4 volts but again, the lesser digits kept rising.

During the time it took to do this, the bulb did dim to orange glow rather than bright white.

 

[laatsch55]

Are Q5, Q7, or Q10 getting hot?

 

[62vauxhall]

I'd put a 20 to 50 ohm 5 or 10 watt resistor in series with the alligator clips to bleed down the reservoir caps.

Best I've got are (2) 10 Ohm 10 Watt. I'd have to get the ones you specify tomorrow morning. So one per alligator clip?

 

[laatsch55]

Those are perfect Gary, use a resistor in series with the jumper between the +/- cap studs to bleed them faster...

 

[62vauxhall]

Are Q5, Q7, or Q10 getting hot?

No, not even warm for the amount of time I've left it plugged in which is not long.

 

[laatsch55]

OK, for the negative lead hook it to the copper bus bar for a good ground, we are going to check the low voltage supplies for Q1-Q4.....the negative can be a gripper, the positive heeds ri have all but the last 1/16 " of probe covered..

 

[62vauxhall]

Those are perfect Gary, use a resistor in series with the jumper between the +/- cap studs to bleed them faster...

OK, I understand using to discharge. Is it touch and remove or leave the resistor in contact with the terminals for a while?

And exactly when and/or how often am I to do this?

 

[NavLinear]

Best I've got are (2) 10 Ohm 10 Watt. I'd have to get the ones you specify tomorrow morning. So one per alligator clip?

Gary,

The 10 ohm will work fine as Lee mentioned. You want an alligator clip at both ends of the resistor as you will connect one end to the + side of the caps and the other to chassis ground to bleed the voltage. After 30 seconds or so measure the voltage and it should be close to 0 VDC. Typically you'll notice a slight increase in voltage after you remove the shunt but that's ok as long as the voltage level remains at a fairly low level.

Edit: To be clear this procedure is to discharge the reservoir caps prior to working on the board.

 

[62vauxhall]

OK, for the negative lead hook it to the copper bus bar for a good ground, we are going to check the low voltage supplies for Q1-Q4.....the negative can be a gripper, the positive heeds ri have all but the last 1/16 " of probe covered..

I have the negative lead to the bus bar and the sheath is on the positive lead. Am I to use it on Q1 through Q4 - E, B or C?

 

[laatsch55]

And that's only to bleed the caps when making a connection to check voltages in a bad place to slip a probe, like on the ack wall.

For now , hook up the hegative lead to the buss bar,turn the amp on and VERY CAREFULLY check what the voltage is at the emitter of Q1 left and right and tell me what ya got...

 

[62vauxhall]

And that's only to bleed the caps when making a connection to check voltages in a bad place to slip a probe, like on the ack wall.

For now , hook up the hegative lead to the buss bar,turn the amp on and VERY CAREFULLY check what the voltage is at the emitter of Q1 left and right and tell me what ya got...

Left Q1...-.567V DC at E
Right Q1.... -567V DC at E

 

[laatsch55]

minus POINT five six seven??