Speedball upgrade fail after a month, voltages way off [resolved]

[goldencalves]

These?

[Paul Birkeland]

Yeah, I would double check that the mounting hardware is properly installed.  If the metal tab of the TIP50 is allowed to contact the heatsink, you will get the issue you're having.

[Deluk]

The solder on the TIP connections looks rather crystalline but that might be due to the trip through the washer. Do they need reflowing?

[goldencalves]

Thanks PB and Deluk. 

I checked the TIP50 assembly, took it apart and reassembled; it had been assembled correctly.  The insulator looks pretty beat up, probably from the wash, with some dents but looks intact (pic attached).

I went ahead and reflowed the TIP connections, then reflowed everything I could reasonably reach on the big board. 

After the reflow, the DC resistance readings:

OA : 60
OB : 126

[Paul Birkeland]

60 ohms? 60K? 60M?

You could carefully power it up and see if the rail voltage stays up above 150 or tanks down like it has been.  That issue that only comes up with the 6080 installed and a 0 ohm resistance at OA or OB on the PC board does point to a transistor installation problem or another slight possibility is a shorted or backwards 100uF cap.

[goldencalves]

Where do I check the rail voltage?

I had it set to DCV, so I believe 60 volts, but I don’t have it in front of me, will have to double check tomorrow.

I did double check the transistors and they appeared to be correctly oriented.

[Paul Birkeland]

The rail voltage is on terminals 2, 4, 13, B+ on the big PC board, and IA/IB on the small PC board.

[goldencalves]

Success!  Thanks so much for bearing with a novice.

All the rail readings were 182v.

The 60 and 124  OA and OB resistance readings from yesterday were in mV (if I am reading my multimeter correctly).

As the OA resistance is still low at 60, should I be attentive to anything in particular going forward? 

And would the flux that I used periodically need to be scrubbed from the connections (IE does it continue to sweat out from the solder points as the points are exposed to heat over time?).

Many thanks again for the assistance.

[Paul Birkeland]

Resistance will be in Ohms, not volts.

Can you double check the DC voltages at terminals 7 and 9? With 182V of B+, the voltages at 7 and 9 are likely either correct or one of them is now 0.

If the flux returns, another round through the dishwasher would be called for, though I can't recall ever having to perform that task twice on the same kit.

[goldencalves]

Oops, I didn’t mean to jump to a premature resolution!  The LEDS were all lit up and I listened to a record without problem before seeing your last response.

DC voltages:
7: regular bounce between 105 and 111v
9: regular bounce between 102 and 108v

[Paul Birkeland]

Those are good working voltages.

-PB

[goldencalves]

Oh excellent!  Thanks again so much.  So glad that I didn't have to save up for a whole new kit!

[larcenasb]

Glad to hear your amp is functioning well now, goldencalves. Enjoy some weekend listening!