left channel went out...

djspacewhale · 2428

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Offline djspacewhale

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on: October 17, 2018, 05:34:04 PM
so this is a fun one... I was listening, had some problems recently with channel hum but resoldered all the grounds and replaced a few wires and it ran good as new for a while, but then earlier today I heard a loud pop in the right channel and it stopped outputting sound at all... after a little while I turned off the amp and turned it over, and one of the heat sinks on the Speedball was still hot while the other was cold. I replaced the wires and resoldered every joint not by the inputs or power supply, and the channel was still out and the heatsink cold. I think I got some wire backwards, though, because now the right channel was outputting and the left was silent. the headphones aren't the problem by that and by me testing them from my phone, the DAC isn't the problem (tried other cable & other audio source (monitor instead of DAC)) the tubes aren't the problem because I've retested with every tube in my collection, and at this point I don't know what else could be the problem. I'm worried the transistor blew out or something (can they even do that?), but lost my instruction PDF so can't remember the voltages/resistances to expect across components and terminals. where I have it now is that the signal is still only out of the right channel, but it is somehow quieter than before (I did move the cable from the top terminal to the bottom on the station by the power tube, but that shouldn't create THIS large a change in impedance/resistance, right??). how in the heck can I troubleshoot this?



Offline adydula

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Reply #1 on: October 18, 2018, 04:38:43 AM
Are all the leds on the 12AU7 on?

Alex



Offline Paul Birkeland

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Reply #2 on: October 18, 2018, 04:41:45 AM
Without knowing what your voltages are, there isn't really any way to provide any direction to your debugging.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline djspacewhale

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Reply #3 on: October 18, 2018, 12:01:11 PM
adydula all of the LEDs on the small board are lit, but one of the LEDs on the 12au7 socket isn't and none on the large board are either.



Offline djspacewhale

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Reply #4 on: October 18, 2018, 01:54:12 PM
I replaced the LED that wasn't turning on, and then took a video of the boards and socket before and after turning on power https://photos.app.goo.gl/YJe4MZwnSihsFaeV9 both LEDS on the socket as well as the 4 on the small board light brightly for a hot second, then one LED goes out, the board darkens, and the large board remains unlit.



Offline fullheadofnothing

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Reply #5 on: October 18, 2018, 02:01:26 PM
Without knowing what your voltages are, there isn't really any way to provide any direction to your debugging.

Joshua Harris

I Write the Manuals That Make The Whole World Sing
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Offline djspacewhale

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Reply #6 on: October 18, 2018, 02:11:12 PM
where do I take voltages? again, I can't find my copy of the build manual, and it sounds like you can only get one with the kit...



Offline LolNole

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Reply #7 on: October 18, 2018, 02:26:58 PM
If you purchased your Crack from them, send them an email ([email protected]) with your purchase information and they will send you another one.



Offline djspacewhale

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Reply #8 on: October 18, 2018, 03:04:18 PM
alright I did some resistance checks between ground and terminals 7 and 9, and terminal 7 was acting as a ground while terminal 9 had a resistance of around 1.6 megaohms which seems wrong lol. editing to say I fixed the ground problem, but now the resistances on B3, B6, 7 and 9 are about 500 kilo-ohms each
« Last Edit: October 18, 2018, 03:26:08 PM by djspacewhale »



Offline Tom-s

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Reply #9 on: October 18, 2018, 10:34:20 PM
Measure voltages.
Not resistances at this point.
As long as the ground path measures 0 Ohms.
With Speedball installed voltages should be measured.



Offline Paul Birkeland

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Reply #10 on: October 19, 2018, 04:42:05 AM
Replacing parts without performing the voltage check and figuring out what's actually going wrong is more likely to cause new problems rather than to solve the existing one.

Most of the time an LED that isn't lighting will have an external factor causing that, not the LED itself.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline djspacewhale

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Reply #11 on: October 20, 2018, 10:02:15 AM
here's the voltages:
1. 76.2V
2. 89V
3. 0
4. 88.5V
5. 52.8V
6. 0
7. 76.3V
8. 0
9. 50.6V
10. 0



Offline Paul Birkeland

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Reply #12 on: October 20, 2018, 10:05:46 AM
If you have 89V at terminal 2, then you have a short between the TIP50 and the heatsink on one or both sides of the large Speedball board.

You can test this by pulling the 6080 and rechecking your voltages at terminals 1-5.  You should see that terminals 1 and 5 pop up to around 80V and terminal 2 (and 4) rise to 200V or so.

-PB

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline djspacewhale

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Reply #13 on: October 20, 2018, 10:19:41 AM
just tried that - my terminals 1 and 5 sat at 74.9 and 72.5V each, and terminals 2 and 4 at 223V each, so it seems that that's problably it. I'll try resoldering the TIP50 then and update



Offline djspacewhale

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Reply #14 on: October 20, 2018, 10:31:28 AM
actually, is it possible the transistor blew? since the audio went out while I was listening and not during any tinkering?