Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: djspacewhale on October 17, 2018, 05:34:04 PM
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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?
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Are all the leds on the 12AU7 on?
Alex
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Without knowing what your voltages are, there isn't really any way to provide any direction to your debugging.
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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.
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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.
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Without knowing what your voltages are, there isn't really any way to provide any direction to your debugging.
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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...
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If you purchased your Crack from them, send them an email ([email protected]) with your purchase information and they will send you another one.
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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
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Measure voltages.
Not resistances at this point.
As long as the ground path measures 0 Ohms.
With Speedball installed voltages should be measured.
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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.
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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
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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
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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
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actually, is it possible the transistor blew? since the audio went out while I was listening and not during any tinkering?
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I'll try resoldering the TIP50 then and update
These are not the instructions I provided.
Your tests reveal that the TIP50 is very likely touching the heatsink. There's a warning in giant text on page 22 of the manual that is where you should start reading to get this issue resolved.
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I got both channels working again! I took apart the board and put it back together, and now both channels are outputting - the right channel is still quieter than the left, though, and as far as I can find from other threads that is a resistance problem? the right heatsink is still less warm than the left, haven't checked voltages yet but I did notice while reassembling that one of the insulating thingies between the transistor and the heatsink was ripped so that might be causing this? is it possible to get replacements for those?
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Yes, you should not run the amp with damaged insulators, and you should never use an amp that hasn't passed its voltage checks.
You are heading down the road of burning up your power transformer, and they are very expensive and time consuming to replace.