Speedball install problems

[ibzrg1570]

I installed the Speedball after finishing the stock build a few months ago and everything was working fine for about 30 minutes before I started hearing loud pops and seeing a bit of smoke. I resoldered some joints that looked off, which resolved the pops and smoke, but now I get no audio on the left channel. After a little more resoldering and reheating the middle lug on the MJE-350 as recommended in the instructions I have a bit of hiss in the left channel but still no audio information. The hiss does not change volume with the potentiometer. Voltage and resistance tests all passed the first time around, and retesting revealed that I was now only getting 5V at OB on the small board and Terminal 5.

I'm wondering if it's possible that a component was damaged or if it's likely to just be more soldering issues that I haven't uncovered yet.

 

[Paul Birkeland]

Pull the 6080 and retest your voltages.

Do both LED's on the 9 pin socket light up?  (If one doesn't don't assume that its connections need to be resoldered)

Smoke generally means that the TIP50 heatsink mounting hardware wasn't installed properly, which will give low voltages at the IA and IB terminals on the small front board, and eventually will blow up one of the 270 Ohm 5W power supply resistors.

-PB

 

[ibzrg1570]

Pull the 6080 and retest your voltages.

Do both LED's on the 9 pin socket light up?  (If one doesn't don't assume that its connections need to be resoldered)

Smoke generally means that the TIP50 heatsink mounting hardware wasn't installed properly, which will give low voltages at the IA and IB terminals on the small front board, and eventually will blow up one of the 270 Ohm 5W power supply resistors.

-PB

Thanks for the reply, Paul. Pulled the 6080 and remeasured.

Small board: OB is 3.8V, everything else is in range.
Large board: OA and OB are both 1.5V, everything else is in range.

The LED connected to A3 does not light up. It did before I installed the SB. The LEDs on the B side of the small board are not lit, the others on both boards do.

I'm getting 190V on IA and IB on the small board, not sure if that rules out incorrect installation of the heatsinks. They look right to me, but I'll post a photo in case it helps.

 

[ibzrg1570]

Getting errors when trying to upload, let's see if this works.

https://goo.gl/photos/PVf8Y5uBVMcipRaaA

 

[Paul Birkeland]

Well, your symptoms would either indicate the center leg of the MJE-350 being a problem (which you've resoldered), or potentially the connection between A4 and A5 is no longer functioning.  Inside the 12AU7, there are two plate structures, can you see the little heaters glowing inside each of them?

 

[ibzrg1570]

Yes, both heaters are glowing.

 

[Paul Birkeland]

Reverse the connections of OA and OB.  This will allow you to narrow down whether you have a board problem, or a problem with the fundamental circuit.  (This may require some extra wire scraps to accomplish)