build question regarding c4s voltages recovering from mistake [solved]

[Audionorth]

Hi,

I'm just completing the SEX 2.1 build w/ C4S. 

Resistances checked out before firing it up . . . other voltages measure correctly . . .however, I measure approx 370vdc on pin B5 and the same on both IB and OB . . . I get the correct 75V on OA . . . I've rechecked my soldering on the C4S board which looks good.  The LEDs all light up etc. 

Maybe the MJE* transistor??

Thanks,
M-

[Paul Birkeland]

Try resoldering the center leg of the MJE350.

[Audionorth]

Bloody hell . . .

I re-soldered the center leg and when checking the voltages on the tube pin I created a short with my DMM probe . . . a beautiful spark it was. . . resulting in the loss of two of the leds on the board and the voltages on the board . . . apparently despite wearing a head set one shouldn't talk and measure at the same time . . .:-/ (yes I know better but no one was watching) . . .

No voltages from the C4S board but the fuse is still in tact . . .

Thanks,
m-

[Audionorth]

I reversed course and temporarily removed the C4S (replaced the 150K resistor). . .

I also noticed inconsistent voltages on B6 (I was getting 30vdc instead of 2.5vdc) so I re-soldered the connections and everything now seems solid regarding correct voltages throughout the amp.   

I also ordered replacement parts for the C4S board since they were relatively inexpensive and wanted to get them on their way to Alaska. . . I used the forum and BOM for information to ensure I ordered the correct parts. . .

Can someone tell me if there is a relatively easy way to test the C4S components (mainly the transistors and LEDs) to determine if my slip of the hand resulted in damage? 

Despite building many prior projects it's always a bit humbling when errors occur but I've also learned they can eventually be resolved with patience and generally assistance from knowledgeable members. . .

Thanks for any assistance provided.

Best Regards,
Mike

[mcandmar]

Sorry to hear about your troubles, sounds like things got interesting..

I've just finished assembling my C4S board so did a quick check, with the multimeter testing diodes in circuit i get .866v on two LED's, and 1.489v on the other two. You can see the 1.5v ones visibly light up while testing.  That might be of some use to you, i've no idea how you would go about testing the transistors.

[Audionorth]

Thanks for the response.

The good news is the amp is up and running and sounds great sans C4S at the moment. . .

Checking the resistances of the Leds, and transistors (out of the amp), I'm getting one side with what I suspect are the correct resistances and the other none or a short. 

This leads me to believe that switching out the affected parts will likely resolve the issue. . .as soon as they arrive from Mouser this coming week . . .

I think the inconsistent voltages I was measuring at B6 (due to the bad solder joint) kept me messing around with these measurements (and distraction/apparent miscoordination . . .   ended up with me shorting the DMM probe between B5 and the 1000uf cap leg . . . which may have tweaked the transistors and LEDs of the C4S. . at least that's my working hypothesis at the moment . . .

I will report back if replacing the parts doesn't rectify the issue . . . in the meantime I can at least listen to music despite my humbled entrance into the BH community . . .

m-

[Audionorth]

I realize this has been a bit of a monologue series of posts but to complete the cautionary tale I replaced the components on the C4S board (I zapped) and all is well. . .

M-