Bottlehead Forum

Bottlehead Kits => Crack => Topic started by: eeyore on March 05, 2011, 02:12:29 AM

Title: Problem with Speedball
Post by: eeyore on March 05, 2011, 02:12:29 AM

I recently took some measurements on the Crack with the Speedball upgrade, and by accident, took a current measurement on the right channels' 150k resistor in the Speedball driver upgrade. Loud spark ensured, and since then there has been a slight smell of burning when firing it up, there wasn't any there before. I took voltage measurements at 1 and 5. At terminal 5, it reams 75V or very close to it, but at terminal 1, it reads 6V. I didn't take any more measurements after that, as I felt that may further damage the amp. All the other LED light up, except for the two on the right channel of the driver Speedball PCB.

Anyway, what do you think I have done? I assume that I have fried one of the transistors. How would I know which one? Since the LED won't come on, at all, I'd assume that they were fried. I measured the voltage drop /continuity on the LED, and they don't work, or measure at all. On the left channel, I measure the voltage drop of D2 as 1.357, and D1 as 0.737V. On the Right channel D2 is 0.550 and D1 won't even register. I assume that D1 was fried, and without the LED bias, the transistors are running crazy.

Assuming it is just the LED that went crazy, the 2N2907 and MJE350 should be fine right? Replacement LED should bring this back to normal?

If so, where do I get a pair of the LED? Or is there something even more deeper?

Thanks for any help in advance.

Title: Re: Problem with Speedball
Post by: eeyore on June 04, 2011, 02:10:16 PM

Just in case this might happen to someone else, I finally got to inspect the Speedball PCB up close. It discovered that 1 of the diodes wasn't biasing correctly and the small 237R resistor was blown, and measuring well over 4k. I am now going to replace all the components except for the 150k resistor.

Lesson for me - try not to short out the CCS by measuring current stupidly.

Title: Re: Problem with Speedball
Post by: InfernoSTi on June 04, 2011, 06:29:40 PM

I know your pain!  When I built my first amp (not a BH), I badly shorted the power supply during voltage testing.  I popped the bridge rectifier for the heater somehow but learned a lot about trouble shooting when the amp didn't work. I also learned how to respect the high voltage inside the box!  My probe had a scar burned across it that was halfway through the metal probe!!!   Yikes!!!

Glad you are up and running again....

John