My crack is smoking [resolved]

[Huffstutler]

Hello all,
After successfully building my crack and making sure that it worked well, I went to add my speedball upgrade, (older generation), and now the resister not over the transformer but right next to the transformer is putting off a little puff of smoke (at least that what it looks like to me)
additionally, on the main board of the speedball, I have three LEDs that light up, and the one that doesn't light up is next to one that lights up very bright. the LEDs on the other two speedball boards light up very dimly. One of the LEDs on the nine pin socket also appears to be dim, next to one that lights up bright.
When I first started to measure the voltage, terminal one was perfect while terminal two barley measured at all. I stopped measuring when I noticed the smoke and am worried about getting further measurements. Do you lads have an idea about how I best go about troubleshooting this?

[oguinn]

It would be helpful to post some pictures of your build. Are your resistance checks coming out ok? You don't need the amp on to check those.

[Paul Birkeland]

You almost certainly haven't properly mounted the TIP50 transistors.  I would go back through the manual and check all those components that are involved in mounting the TIP50 to the heatsink.  Those components function to prevent the metal tab from the TIP50s from touching the heatsinks.  If they touch, then you'll get the issue you're describing.

[Huffstutler]

All of my resistors check out with the exception of the one on terminal 12 and 13, is it normal to get sporadic readings on that one? I looked over the tip50, but I don't see that I installed it incorrectly or that the transistor is touching the heatsink. Should I go ahead and reassemble it to be safe? Here are some pictures

[Deke609]

Don't know whether this could relate to the issue you're having, but I'd double check that the circled diode leads in the  attached pic aren't touching or close to touching. It also looks like there's a lead coming from a diode on the opposite side of the terminal strip that needs trimming.

cheers, Derek

[Huffstutler]

Thanks for the find! Unfortunately, it didn't fix the issue as my LEDs are still out of line.

[Paul Birkeland]

Can you measure the DC resistance between ground (terminal 12) and OA and OB on the big PC board?

Does the 270 ohm resistor get hot if you run the amp with just the 12AU7 and no 6080?

[Huffstutler]

The 270 resistors did not get hot, and 0A and 0B both read .4 on 200v on DCV when the amp was turned off and .8 when turned on (with the 6080 removed). 

[Paul Birkeland]

Can you set your meter to ohms and measure the DC resistance between OA and OB on the big board and ground on the amp?

[Huffstutler]

Forgive me for being ignorant, but when you say OA and OB, do you mean the O on top and bottom of the main speedball board?

[Paul Birkeland]

Sorry, it's the old boards (the new ones are labeled slightly differently).  Yes, each "O" pad on the big board to ground would be what I'm looking for.

-PB

[Huffstutler]

Okay, would there be a reason that I wouldn't get a reading from either O?

[Paul Birkeland]

You'll get some kind of reading.  It will wither be close to 0 ohms, or it will be over the limit "OL".

[Huffstutler]

Okay, I am getting OL on both regardless of how high I set my multimeter to, and I noticed that the heatsink close to the top of speedball gets hot while the other heatsink remains much cooler.

[Paul Birkeland]

Can you post some pictures of the bottom of the large PC board?

Can you also remove the 6080 but leave the 12AU7, then report the I and O voltages on the smaller PC boards?

-PB