Bottlehead Forum
Bottlehead Kits => Kaiju Stereo 300B amp => Topic started by: joepiecuch on July 01, 2019, 02:24:16 PM
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As posted previously, I'd built and mounted the C4S boards and was engaged in the driver testing when I believed I accidentally shorted either the IA or OA pad to a transistor leg with a VOM probe. This happened after getting good readings at IA and OA and then adjusting the trimpot to get a good reading at 46U. In other words, everything seemed fine, and then I made a slip in a recheck with catastrophic results (or so I thought). The 90.9 ohm resistor and two A-side LEDs exploded pretty dramatically. I built a new board, installed it and fired it up. As I sat waiting for the B-side LEDs to glow, the same thing happened again: the resistor and LEDs blew, without my having gone near it with a probe. Correlation was, apparently, not causation. Everything had passed muster through the high voltage power supply test, and starting from that point in the manual, I've reviewed all the connections and don't see what I am missing. But there must be something! Any suggestion (s) where to start would be much appreciated.
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I would be looking very, very hard at the five black zener diodes mounted by that 9 pin tube socket. Are they all properly oriented? Is anything touching that shouldn't be?
I would also swap the 5670s between sides. Though a completely shorted 5670 shouldn't destroy the PC board, it would be good to rule it out.
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Well...it looks to me as though the orientation is correct, and that there are no inappropriate contacts, but more eyes are always better. Am I safe powering up without the driver tube on the problem side to test both tubes on the good side?
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Did you install new zeners? If I remember correctly the blowed up LEDs thing has usually proven to be a side effect of the zeners being shorted. If we didn't give you new ones with the new board setup we should have, and we'll give you a new set of parts. Sorry about that!
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No apology necessary! I thought the problem was more localised; didn't get or install new zeners, and the existing ones tested as shorted just now. Is it possible then that I did after all short the transistor leg, frying the zeners, which then resulted in resistor and LED explosions both times?
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Yup, that's what I'm thinking happened, and I should have put 2 and 2 together. I have done it myself, probably more than once... So new board, new zeners.
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I'm in good company, then. I'm dismantled and ready to take another shot at it. Thanks very much.
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Zeners and new board installed and voltages check within spec. Thanks all for the outstanding customer service and support.