Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: sjeffrey on June 24, 2015, 04:52:28 PM
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I'm having issues with my crack/speedball.
I've been a happy user for almost 2 years now using it for a couple of hours a day. Earlier this week I went to use my crack and there was no sound.
I checked the obvious things like DAC input, volume, sound card, etc. Convinced it was my crack I carefully turned it over and turned it back on.
That's when I noticed none of the LEDs are lighting. The 2 tubes are glowing so it seems they are getting power. The amp wasn't moved or hit or anything before it stopped working.
Tonight I figured I had a bit of time to trouble shoot so I pulled out my DMM and went to work. Well the voltages dont make any sense. It's a cheap DMM but it did the job just fine for my initial build. Maybe things are really out of wack?
EDIT: I forgot to mention that a visual inspection doesn't reveal anything that looks of concern. No obvious blown capacitors or anything.
It would be great if could get some guidance on what to do next.
Thanks!
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I think You need to post the voltages. Stock by the way?
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That's the problem. When I try to get readings the voltage is all over the place and not stable at all. I was hoping there would be a component that would cause something like that.
The amp is stock with speedball upgrade. I also tried different tubes with same results.
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Maybe a bad solder joint right at the power input?
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Which power input are you refering to?
The tubes light up so I doubt there's an issue at the main power cord.
I ordered a better DMM (Fluke 117) so hopefully I will receive that shortly and be able to provide better readings.
In the meantime I appreciate any ideas.
Stephane
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If the tubes light up like they did before, chances are the heaters are getting around the right voltages. Have You really measured all voltages and they are all wrong?
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I had my DMM on DC and tried to mesure a bunch of terminals with the negative lead on T2 and the readings were just all over the place.
Nothing was remotely stable and sometimes the number would be negative.
I figured it was either really screwed up and didn't want to leave the power on too long or it could be my DMM that's too cheap.
Stephane
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I had my DMM on DC and tried to mesure a bunch of terminals with the negative lead on T2 and the readings were just all over the place.
Terminal 2 isn't a ground.
When you say they are all over the place, are they all over the place on the full volt scale, or millivolt scale?
-PB
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I probably meant 12, I am going from memory.
The dmm readout would jump to different numbers constantly. The decimal would show low voltage numbers to thousands and even to negative.
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I probably meant 12, I am going from memory.
The dmm readout would jump to different numbers constantly. The decimal would show low voltage numbers to thousands and even to negative.
Those are the meter struggling to resolve what is basically 0V.
A loose black wire would create a disruption in the ground path to terminal 12, which would cause all of this.
Terminal 20 is the first ground point in the power supply. Carefully measure the voltage from 20 to 21 (it may be somewhat live, even with the amp off, as the tubes are unable to siphon off the voltage).
-PB
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Well I think we are on to something here.
With it powered off for over 16 hours the reading between 20 and 21 was at 2 and was slowly going down. Turning it own it climbed to just over 2 and hover there.
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Turning it own it climbed to just over 2 and hover there.
2v? 2Mv? 200V?
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Sorry 2V
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Ok. I just tried again after letting the types heat up a little and voltage was steady at 240V between T20 and T21.
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Ok. I just tried again after letting the types heat up a little and voltage was steady at 240V between T20 and T21.
The voltage will appear instantly between T20 and T21.
240V means that it's not making it to the tubes themselves. You have a loose wire or a flaky solder joint in your amplifier preventing this most likely.
-PB
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Amp is back up and singing nicely ;D
Must have been a bad solder somewhere. Strange that it worked fine for so long.
Makes me have more sympathy for products you buy that suddenly die 3 months after warranty is up. ???
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Did you find the bad solder joint and fix it? If not the chances are very high that it will cut out again.
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I just reflowed all the joins involved around T12, 20, 21 and others that were easy to get to.
I'm a bit paranoid about getting shocked so I didn't really want to do 1 joint at a time and retest. I let it sit for an hour before taking the solder tip to them to be safe.
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Did you find the bad solder joint and fix it? If not the chances are very high that it will cut out again.
You called it a year ago,
amp cut out again. Guess it's time to inspect each solder one by one.
Is there a trick to drain the voltage between 20 and 21 so I don't get zapped or have to wait 24 hours before soldering?
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A properly built amplifier will drain off voltage in about 5 minutes through the bleeder resistor. If your power supply is incomplete, it may not have that path, so the voltage will remain high for a long time. If you need to know what voltage a point is at, measure it.
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I just measured the voltage 24 hours later and it's still at 156V.
I know the power supply's path is incomplete somewhere but is it safe to poke around?
I would rather there be no voltage but waiting several days for it to go to 0 is impractical.
What can I do?
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Do you have the 270K resistor installed?
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Do you have the 270K resistor installed?
I do, from U12 to U13. The solder there looks fine.
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What voltage do you have between 12 and 13?
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What voltage do you have between 12 and 13?
Between 20-21 it was still 147V after 48 hours.
I assume you wanted between 12 and 13 with power on and it was .018V and slowly climbing to .022V after about 5 seconds with probe on.
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Since the voltage isn't bleeding off, either one of the 270 Ohm resistors or the black wires connecting between the striped sides of the 220uF capacitors is missing or not well connected. If you poke around with a chop stick, you should be able to temporarily restore the connection.
-PB
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Since the voltage isn't bleeding off, either one of the 270 Ohm resistors or the black wires connecting between the striped sides of the 220uF capacitors is missing or not well connected. If you poke around with a chop stick, you should be able to temporarily restore the connection.
-PB
I'm stomped. So tapping with a chop stick I was able to restore a connection and therefore drain what was stuck at 20-21.
I looked at all back wires around 12-16, made sure everything was there. Capacitors are correctly installed. I couldn't find anything wrong. I reflowed the solders in that area. It's really crammed in there. At first it didn't help but with more tapping around and push of wires it came back to life. I wish I knew which one is the problem as I reflowed everything and that didn't directly fix it. I guess I'll be looking at this again next year :-[