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March 31, 2023, 06:38:23 PM

Author Topic: Oops! Blown component on pcb  (Read 986 times)

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Offline gsharri

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Oops! Blown component on pcb
« on: December 07, 2022, 06:07:33 AM »
I have a pair of 300b Paramounts which were modified by Paul Birkeland to use a 6LU8 driver tube. I installed a pair of NOS 6LU8s and one of them was apparently damaged in shipping (tested good before shipping). The result: a flash of light and a "snapping" sound as D1 blew it's guts across the pcb mounted below the 6LU8 tube (see pic). What type of LED do I need for replacement and how do I test for proper operation? I have no schematics or manual as I purchased these used.
Thanks
Scott

Offline Paul Birkeland

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Re: Oops! Blown component on pcb
« Reply #1 on: December 07, 2022, 06:18:03 AM »
Just replacing the LED is rarely sufficient to perform this kind of repair.  Typically I would remove both LEDs (they are HLMP-6000), Q1, and Q2, then test R1 and R2 with the transistors removed to be sure they are still happy, then repopulate the board.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline gsharri

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Re: Oops! Blown component on pcb
« Reply #2 on: December 07, 2022, 07:32:41 AM »
I will do that. Thank you sir.

Offline gsharri

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Re: Oops! Blown component on pcb
« Reply #3 on: December 31, 2022, 07:46:12 AM »
What are the correct wattage ratings on R1 & R2 if they require replacing?
Thanks

Offline Paul Birkeland

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Re: Oops! Blown component on pcb
« Reply #4 on: December 31, 2022, 08:59:11 AM »
R1 can be an 1/8W part.  You'd want the 90.9 RN55D to get about the same part as what's there.  R2 is a 300K 3W PR-03 resistor.  If that's not available, the RR-03 is functionally about the same.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline gsharri

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Re: Oops! Blown component on pcb
« Reply #5 on: February 04, 2023, 01:10:20 PM »
Okay, a little bit of progress. I have replaced D1 & D2, R1 & R2, and Q1 & Q2 (B side of the board). After powering on with tubes installed D1 & D2 on the B side light up and D1 & D2 on the A side light up briefly and then go out. I get audio out of the speaker but at a very, very low volume.
Recommendations on what to check next?
Is it possible to obtain a manual and schematic?

Thanks, Scott

Offline Paul Birkeland

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Re: Oops! Blown component on pcb
« Reply #6 on: February 04, 2023, 05:25:26 PM »
You really need to measure voltages before trying to use the amp.  Without knowing what the voltages are on that PC board, there aren't any recommendations that can be made.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man