Bottlehead Forum

Bottlehead Kits => Crack => Topic started by: micheld on January 09, 2024, 03:26:56 AM

Title: Left channel dead! [resolved]
Post by: micheld on January 09, 2024, 03:26:56 AM

Morning
Crack with Speedball
Running splendidly for months.
Yesterday all over sudden there was a loud crack (no pun intended) in the left channel and then no sound from that channel.

This morning:
changed the output tube
still no output from the left side
changed the input tube
still no output from the left side
Changed both tubes
still no output from the left side
(btw, the preamp has output from both channels and the Crack has output on the right)

flipped the unit over and  I read 5meg from B3 and 0 ohm from B6.... definitely not the values I was hoping to see. They should be equal and in the kilo ohms range.

Terminal Voltage (DC)
OA almost no reading
OB almost no reading
G 0V
B+ almost no reading

So what next? how could I narrow it down to the fault?

thanks

miche d

Title: Re: Left channel dead!
Post by: Paul Birkeland on January 09, 2024, 04:44:12 AM

Take the large Speedball board out and set your meter to beep for continuity, then test each transistor on the large C4S board for shorts between each pair of transistor legs.  Also be extra sure that the metal tab of the TIP50 transistor isn't making metal to metal contact with the heatsink.

Title: Re: Left channel dead!
Post by: micheld on January 09, 2024, 06:45:03 AM

UPDATE

Found the issue
The backside of the 100 µf cap connected 6U/7U was shorting on the ground wire connected to the Speedball

Moved the cap so this issue not repeat itself.
Wonder how for many months this issue did not manifest itself...

Thanks

michel d