Derek92994's 700 Ser II White Oak conversion

[laatsch55]

Darc, hook your meter up to backplane ground test point and "out" test point. Watch voltage during power up DC Mv.

 

[laatsch55]

Check both channels..

 

[derek92994]

Lee and George S, thanks for the tips. I will look at this tomorrow after sleep, quite drunk right now.

 

[laatsch55]

I would hope so!!

 

[George S.]

Yeah, good idea to wait!!!

 

[Skratch]

Its New Years Day down under

 

[Gepetto]

Mouser has run out of MJ21196G's with none available until May 2022, hope you guys have got spares.

DigiKey has plenty Darcy...

 

[derek92994]

Yep, new years day, and no hangover, quality scotch. Sure woke up late though.
Does anyone have a mouser part number for the KOA Speer 3 watt metal film 2%, .33ohm emitter resistors?
My plan is to order 6x 95G's and the resistors from mouser to get free postage. I will get 6x 96G's from digikey (thank you Joe).

 

[derek92994]

Reseated and made sure connectors were tinned on the DCP and control board. Made sure capacitor and bus bar connections were tight. Tidied up soldering and cleaned flux off on the underside of that connector thing on far left hand side of amp. Double checked all connections.

Brought her up on variac and dbt. Gets to maybe 80-100 volts, bulb is glowing then suddenly goes much brighter than it should. Fuse blows (using 2 amp for safety) will post pic of fuse that blows.

Wtf is going on?? Then I find a slightly swollen cap on the right backplane. All the others are flat but this one sure isnt. And its right next to the first output that blew the first time the amp faulted (4th from top).

Plenty of pics:

 

[derek92994]

So glad I used variac and dbt, could have hurt something

 

[George S.]

Your right, that cap looks like it has issues. I'm thinking you've found the problem. In one photo it looks like the side is slightly bulging, and in another photo the top.

 

[Skratch]

Does the fuse coordinate to the capacitor that's in question? A B+ or B- fuse

 

[derek92994]

Thank you for the replies. I shall get some rest and investigate further tomorrow. I welcome anymore advice on the repair path I should take. That backplane will have to come out to replace the capacitor and I do wonder how much life the other capacitors have on this and the other backplane. It may be wise to replace them all. Lets see what Lee and Joe think about this issue.

 

[laatsch55]

Cut the cap off the board and leave it out and bring it up again. Dont desolder the cut off pins yet.

 

[laatsch55]

That cap cleans rail voltage on that board. Not absolutely necessary..

 

[laatsch55]

I have run some without it after blowing some on those first generation backplane. Have also replaced them without pulling the boards by laying them on the side..

 

[laatsch55]

If you can disassemble that cap and leave 1/8 to 1/4" of leads sticking up that will help..

 

[derek92994]

Thank you Lee, will do after breakfast, will also trace where that fuse goes to.

 

[derek92994]

Removed cap, traced blown fuse to fused B+1 on right backplane. Brought her up on DBT, relays kicked in around 180/190v as per normal.

Moving forward, bypass variac and dbt, power up direct, idle for 5 mins, set bias to 365?
Questions:
Do I keep the 2 amp rail fuses in?
Do I still avoid using the P 3600 Pre?

 

[laatsch55]

Yes, keep it hooked up and running for awhile...