Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: FairDinkum on August 28, 2014, 08:37:21 AM
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My Crack works ok before the installation of Speedball. After installation, the voltages appear fine except for terminal 9, which starts high (180s) and gradually decrease. Upon listening, the left channel is dead. :(
There were 2 incidents during voltage checks where there were sparks: the first time when the negative (black) test probe with alligator clip tester on terminal 12 came loose and touched terminal 13. In the second incident, I was shaking too much while testing terminal 7. ;) I shut down the amp right away. I hope I haven't short circuited anything.
Your help is much appreciated.
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The experts are here soon to help, rest assured.
Just a thought, a short between B5 and B6? Happens for example if leads are too long, at the sockets they might rather easily shift. Pictures of the octal sockets solders and the adjacent termnal strip available?
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Rightio I'll check and take photos.
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Here are the photos of the octal socket and terminal 9. I've also attached the voltage readings.
Meanwhile, I'll reflow 9U.
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Did an ohm check on terminals 7 and 9. Both appear to be increasing (charging) but the former is showing 6-ish mega ohms and climbing while the latter starts at 1ish. Not sure if this is normal. The test was performed after I've reflowed terminal 9. Near in mind I've done the grounding mod on the volume pot per the sticky thread in this forum.
Thanks for any suggestion you might have.
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More photos of the octal socket and the terminal strip.
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Plot twist! One of the LEDs on the big PCB is not working.
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Try reheating the center leg of the TIP-50 feeding T9.
Also, just to double check, you did install the thermal pads and shoulder washers on the TIP-50's?
-PB
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Try reheating the center leg of the TIP-50 feeding T9.
Also, just to double check, you did install the thermal pads and shoulder washers on the TIP-50's?
-PB
OK I'll reheat the center leg for both TIP-50. And yup I've installed the clear thermal pad and washers.
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Reheated the center leg of the TIP-50 closest to the volume pot on the right. A few seconds after switching on, both LEDs are now not working and there's some sparking under the PCB. I switched it off immediately. :(
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Sparking under the PC board would indicate a loose connection or a loose solder blob shorting out components.
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Ok. What I'm going to do is to completely detach the main PCB and troubleshoot from there. How do I check to make sure the components are working, especially the TIP-50? Just resistance checks?
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You can measure the resistance between each pair of pins. When they fail, they fail shut.
Also check the 2N2222A.
-PB
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Hmm I'm not sure where the problem is under the PCB (right side of the picture). Here's a photo of the soldering job of the TIP-50.
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Throw it back in and check voltages.
-PB
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Ok. I've cleaned the board up anyway and tested the components via the back of the PCB. The components look ok.
Not looking forward to the voltage checks but I guess it has to be done.
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I've put the PCB back after checking the soldering etc. No spars this time but unfortunately the same set of LEDs is still not lighting up. Should I attempt to replace them?
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I'm not an expert here, but (per your last picture) it looks like small resistor is fried.
I hope PB can chime in soon to guide you a little further.
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Nice catch! Kris is right, that wide back band says it is toast.
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That's just the shadow from the flash I think. ;) here's a better picture.
Edit: just measured the resistance of that resistor. It's giving me a reading. I presume that if it's blown I won't be able to get a reading.
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I see a a small dark spot. But to be sure throw a meter across it. The manual will give you the resistance.
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I see a a small dark spot. But to be sure throw a meter across it. The manual will give you the resistance.
Oh my gosh the resistance is way off! It's not measuring 31.6 ohms at all! I'll replace the resistor tomorrow. Nice pick up!
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Alright just to clarify: I should shop for a 31.6 ohm 1/8 watt film resistor. Does it matter what tolerance it is or the manufacturer?
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First lift one leg of the resistor to make the resistance check. It is probably in parallel with something that will mess up the resistance you read.
Only one lead needs to be lifted, that takes it out of the circuit.
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First lift one leg of the resistor to make the resistance check. It is probably in parallel with something that will mess up the resistance you read.
Only one lead needs to be lifted, that takes it out of the circuit.
I did exactly that and it's showing 320 kilo ohms when it should be 31.6 ohms.
Now I'll just have to go find a replacement and test it out! Thanks guys!
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First verify the color code. If it is correct according to the manual you need a replacement. Bottlehead will send it or you can source it locally, maybe faster.
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I would measure the other 31.6 Ohm resistor to be sure your meter will measure it properly.
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Thanks Paul. The other resistor is measuring 31.6 ohms on the dot. I hope that this is the main problem. As I recall, initially only one of the LEDs didn't light up, and I proceeded to reflow the center leg of the TIP-50, leading to sparks under the PCB which must have blown the resistor. Hopefully both LEDs will light up with the replacement of this resistor.
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You are not reflowing with the Crack turned on, are you? That is not a good idea.
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Generally a resistor goes like that because it drew way too much current (during that spark, the source of which we don't know). So you have treated the symptom but not necessarily the cause of the symptom. I would follow PBs suggestion and check the resistance between each pair of pins on the transistors. Measure the resistance between each possible pairing of the three transistor leads on the 2N2222A and also check the TIP50 the same way. If you see a very low (under 100 ohms) reading across any pair the transistor is blown.
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Thanks Doc. Do I have to remove the transistors from the PCB for the resistance check? If not, can I measure them on the back of the PCB?
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You should be able to measure them on the board.
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I've performed the resistance checks for both pairs of TIP-50 and 2N2222A (see picture). I've measure the TIP-50 using the pins on the top side, and the 2N2222A via the bottom of the PCB. The TIP50 readings are similar for the pair; but not the 2N2222A. In fact, on the "bad" side, one pair of the legs for 2N2222A is showing 17 ohms, which is unusual given that the resistance on the same pair of legs on the "good" side shows rapidly rising resistance to OL. I'm using a Fluke 87V.
Does this mean the 2N2222A on the "bad" side is broken, hence causing the resistor to break as well? If so, looks like we might found the problem.
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yup.
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Hi Doc - thanks so much for helping me out! I have a lot of trouble sourcing that resistor here in Australia. It's an uncommon resistor and so far I haven't found any. I think I might be able to source the 2N2222A. In any case, would you or Eileen mind sending over some resistors and 2N2222A? This is to ensure product consistency. I don't mind paying for them. My order reference is #2521.
Thanks very much!
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Yeah the resistor is kind of an umcommon value and needs to be accurate. Best bet is to contact Eileen directly at queen at bottlehead dot com and she can be sure she has all the info she needs to make sure you get the right parts. Bear in mind it's a three day weekend here (labor day) so the parts may not mail out for a couple of days.
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Thanks Doc I've emailed the Queen. Is there possibly a component failure up chain that could have caused the 2N2222A to blow? The LEDs or the TIP-50 on the same side maybe?
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I'd like to update this thread to say that I've received the replacement LEDs and resistors and I've replaced both the LEDs and the blown 31.6ohm resistor in the defective channel on the main PCB. Voltages on 7 and 9 are 103.3 and 106.5 volts (is this discrepancy normal?), and the other ones seem to check out ok. Hooked the amp up to a source and I heard sweet sweet music. :)
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Voltages on 7 and 9 are 103.3 and 106.5 volts (is this discrepancy normal?)
These voltages are dependent on both the 6080 itself, as well as the 12AU7 plate voltages (T1 and T5), some variation is certainly expected.
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Thanks Paul! This means that my issue is solved. Thank you everyone (including the Queen) for your help! I've had a lot of fun building my first electronic project. :)