Building a Pearl 2

[KevinHeem]

I see that now looking back at your previous posts/pictures. I've got you pics up on the big screen I can't find anything wrong..yet.

 

[Dneu2011]

Same here. I researched and overlooked everything before posting here. I have yet to plug it directly into the wall in fear of damaging anything else since it has not passed the Dim Bulb Tester yet..

 

[KevinHeem]

I think the polarity of the caps on your positive rail are reversed.

 

[KevinHeem]

But I'm not sure...I'm checking, getting confused myself.

 

[Dneu2011]

Its the positive rail drop resistor that is over-heating. I following 6l6's pictures and schematic on the first post when making it.

 

[KevinHeem]

I'm starring at your third picture from post 1845 and comparing it to the schematic. Shouldn't the wires from the positive side of each rectifier go to the positive post of the cap.

 

[KevinHeem]

Sorry it makes sense to me now. it's good

 

[KevinHeem]

Have you tried connecting one Pearl II board at a time?

 

[KevinHeem]

I tested each board individually...

Guess that answers my question.

 

[Dneu2011]

Haha. Yes i did. I appreciate you helping troubleshoot.

 

[KevinHeem]

I leave your pics up on the big screen and come back and meditate on them from time to time...nothing yet.

 

[6L6]

The PSU looks correct.

If it tested OK without the pearl PCBs attached, then it's likely not the issue.

That only one of the filter resistors is hot makes me think it's a short on the V+ side or something similar.

Did you measure the on-pearl regulators on both boards both sides?

 

[Dneu2011]

Yes, I tested the regulators before stuffing the rest of the boards. I listed my results on POST #1847. I can attempt to test them again by lifting the resistor leds for R4, R3, R33, and R31.

On the regulators, both should for sure be isolated from the heatsinks, correct? I reviewed the data sheet for the 7824 & it says "heatsink surface connected to Pin 2" which is ground. Should the rubber pad I used between the heatsink and regulator be removed?

I am using part #863-MC7824CTG on Mouser.

 

[McQuaide]

Could one of the heatsinks be shorting against something? I'd remove them completely.

 

[KevinHeem]

Just to be clear...you tested the boards individually and the dropping resistor overheated using either one?

 

[KevinHeem]

Also, the positive rail is conducting more than the negative, right? I don’t see the burn marks on the negative dropping resistor.

 

[KevinHeem]

Does it matter where P1 is set on start up?

 

[Dneu2011]

First thing I just tried this morning was removing the 7824 on one board from the heatsink and "voila!" No DBT light coming on and no hot resistor. The regulator resistors (3,4, 33, and 31) are reading +-24V.

Now I just need to figure out if the heatsink is shorting out or if the 7824's need to be connected directly to the heatsink without an insulator. The data sheet for my device (#863-MC7824CTG) says the ground pin 2 needs to be connected to the heatsink.

Does this look correct on the datasheet? Picture attached.

 

[Dneu2011]

Yep... I just attached the 7824 directly to the heatsink without insulator and it powered up perfectly and I was able to set DC to 0mv on the one board hooked up.

I will hook up the second board, test the regulator without insulator, then wire the rca wires and reset DC offset with inputs shorted.

Should I still put thermal paste between the 7824 and heatsink or just leave it as is?

 

[Zen Mod]

if heatsink is (in any way, deliberately or not) in electrical contact with circuit, then you must isolate regulator electrically from heatsink

simple as that

The data sheet for my device (#863-MC7824CTG) says the ground pin 2 needs to be connected to the heatsink.

datasheet is saying nothing else than that pin2 and back tab are electrically in connection, not that they need to be connected