Crack with Speedball - smoke and burning hot!

[canuckaudio]

Hi All.

First off, I love my crack with speedball and have been running the speedball upgrade for months without issue.
This week, I smelled smoke from the unit. Moved my hand close and felt lots of heat coming from it. I turned it off, unplugged it, then turned it over and a bunch of smoke came out.

Upon further inspection, I noticed that the wire connecting the power switch to the power transformer has been damaged (melted) from being to close to the 270 ohm 5W resistor that is connected to terminal 13L and 15L.
At first, I thought I could just replace the damaged wire which is probably where the smoke came from but would it resolve the high temp issue (the plate was burning hot -- I've never felt that much heat coming from the unit)?

Thanks!

[Paul Birkeland]

I would recommend measuring the DC voltages in your amp.  Do you have the rubber feet installed on the wood base?

[canuckaudio]

Yes rubber feet are installed. I'll post an update after I do the DV voltage check. But first, I'll replace the damaged wire.

[canuckaudio]

And thanks for the super quick reply PB!

[Deluk]

If the soldered joint on either end of this wire is compromised in any way it will lead to a high resistance connection. Result is HEAT. It will gradually get worse and I'm guessing that with yours it's now getting hot enough to burn things. A new wire, nicely soldered in, may well cure your problem.

[canuckaudio]

Update:

• I replaced the damaged wire connecting the power switch to the power transformer.
• Was going to do DC voltage check but voltmeter battery was dead 
• Decided to turn on the amp and give it a try. Result: lots of static. 
• A couple of weeks go by - ready to try again with a fresh battery in my voltmeter
• Start with a resistance check starting with OA. Loud spark on first contact! 
• After, everything seemed normal so I proceeded with voltage checks
• All DC voltage checks OK -- values below if anyone is curious
• OA and OB 58V
• B+ 156V
• IA and IB 155V
• B-A/B 0V

End result, smooth sound is back! 
Thanks for the help and support

[Paul Birkeland]

• Was going to do DC voltage check but voltmeter battery was dead 
• Decided to turn on the amp and give it a try. Result: lots of static. 

If you don't pass the voltage checks, you could damage your headphones or your body by just trying the amp out.

• OA and OB 58V
• B+ 156V
• IA and IB 155V
• B-A/B 0V

Your B+ voltage is awfully low.  What's your wall voltage?  The 58V at OA and OB is also a bit on the low side.  Typically I would expect around 50V at one of those terminals if a PN2907 was installed backwards.

[canuckaudio]

Thanks for the warning. I won't just "try it" again in the future.
The wall (power bar outlet) voltage measure 118 V.
The PN2907 appear to be installed the right way.

[Paul Birkeland]

I would reflow the solder joints on that small board.  You need to heat the solder joints until the solder flows through the board to the other side (don't add solder to the other side though that's hot helpful either).

[canuckaudio]

That'll be the next weekend project. Thanks