700B blew one Right channel 5A supply fuse

[62vauxhall]

Check fuses gary...

All fuses are good.

 

[laatsch55]

Ok, drop all 4- 5 amp rail fuses, turn it back on , all the way, then check each post in the rectifier...ac fot the ac of course and DC for the DC...

 

[jbeckva]

The collector should be isolated from ground by the mica isolator / Sil-Pad.

Good point, did not think of that.

I think what Nav is getting at is you shouldn't have a short from the case of the 410's to ground. Is that with the rail fuses pulled? If it is, pull it and then measure from the socket's collector lead to ground... if you still have a short at that point, then it could be any of the outputs having a failure on their insulator. Pull them one at a time until the zero ohm to ground goes away.

But again all depends on if you had the rail fuses in or not. With the rail fuses in, your "short" could very well be residual voltage coming from the PS caps.

 

[laatsch55]

Get zero - to bus bar or chassis.

God, how did I miss this...Gary is that zero ohms, or OL ??

 

[laatsch55]

You did have the grey sil-pads under the 410's????????

 

[62vauxhall]

Ok, drop all 4- 5 amp rail fuses, turn it back on , all the way, then check each post in the rectifier...ac fot the ac of course and DC for the DC...

Fuses are out - variac at 120 volts.

Did I understand right - determine which are AC and which are DC posts on the rectifier?

DC: 142.4 volts
AD: 107.0 volts

 

[laatsch55]

Yes, but reference ground at the bus bar and check all 4 posts, also was the ground check result on the 410 case zero ohms or OL?

 

[62vauxhall]

You did have the grey sil-pads under the 410's????????

Yes. Sil pads were in place.

 

[62vauxhall]

God, how did I miss this...Gary is that zero ohms, or OL ??

That was ZERO ohms and fuses were in.

 

[laatsch55]

Check the rectifier posts one at a time, then power down again, with rail fuses out you should have OL on the meter when referenced to ground with the red lead on the 410's case....

 

[NavLinear]

You did have the grey sil-pads under the 410's????????

They've been used more than once and that may be a problem - aka the condom syndrome.

I'm thinking that for trouble shooting it's ok to use the Sil-Pads multiple times but I've never done that so it's something to look into.

Jer has a good point - we'll need to wait and see what Gary says. I think he is bleeding the reservoir caps with a 10 ohm resistor.

 

[jbeckva]

That was ZERO ohms and fuses were in.

Pull fuses.. recheck. If you still have zero, insulator breakdown... or those 4uF caps that go between the tie points (the pos and neg rails) and ground. Or a cat whisker wire ya can't see yet...

 

[62vauxhall]

Yes, but reference ground at the bus bar and check all 4 posts, also was the ground check result on the 410 case zero ohms or OL?

Ground to bus bar - variac at 117 volts - fuses out.

DC post voltage 83 volts
AC post voltage 62.3 volts

410 case check was ZERO ohms and fuses were in then.

 

[laatsch55]

No minus volts on one of those posts ?? Check that 410 case now with no fuses in....

 

[62vauxhall]

Pull fuses.. recheck. If you still have zero, insulator breakdown... or those 4uF caps that go between the tie points (the pos and neg rails) and ground. Or a cat whisker wire ya can't see yet...

Fuses are out still get zero OHMS.

4uF capacitors????

tomorrow durung the day I can fire up my air compressor and blow out any debris. I live in a second floor condo and think running an air compressor after 7PM contravenes some strata rule.

 

[laatsch55]

Jer is referring to the caps on the back wall wher those pesky diodes are, yours are .33uf I believe...

 

[62vauxhall]

No minus volts on one of those posts ?? Check that 410 case now with no fuses in....

Sorry, yes one plus 83 volts and one minus 83 volts.

 

[laatsch55]

OK, the 410 short is a very bad thing, is it on the right channel?

 

[jbeckva]

Fuses are out still get zero OHMS.

4uF capacitors????

tomorrow durung the day I can fire up my air compressor and blow out any debris. I live in a second floor condo and think running an air compressor after 7PM contravenes some strata rule.

Pull the 410 where you are getting the zero from, then measure between it's collector lead (or where the screws normally go) and ground.

These caps here ... the orange guys. Also those diodes that go between the leftmost and rightmost tiepoints on the center terminal blocks.

 

[62vauxhall]

Jer is referring to the caps on the back wall wher those pesky diodes are, yours are .33uf I believe...

Do you mean the 4 capacitors I attached to the rectifier posts? I can't tell what value they are.

If not, the only other capacitors (not on the board) are one between the AC leads to the rectifier and those in the area of the input jacks.