Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: illusineer on September 11, 2020, 04:35:57 PM
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OA - 110V
OB - 102V
G - 13V
B+ - 206V
One of my voltages ain't right :-\ it also reads 13v on the small board test for B-A/B. I plugged in my headphones and only got sound from the right. My amp was working fine before I put the pcbs on it. Also when I was soldering wires on the terminals for the big board sparks popped near the capacitors while I was affixing the wire ends with my pliers (this was after cutting out the 10k 3ws and before putting the big board on). The amp was unplugged but didn't blow the fuse, idk if that has anything to with it or I shorted out the capacitors somewhere while they still had charge.
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Please don't plug headphones into an amp that isn't working, as you may end up with headphones that also don't work.
13V on G means you have 13V on terminal 3 as well. One of the black wires in your amp isn't well connected and is causing this problem. This is not a Speedball issue. I would reflow every solder joint in the amp where a black wire connects, then recheck G on the big board.
On the other hand, if your meter says 13mV, that's 0.013V and is plenty close to 0V to be ignored.
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I tested again, and what I noticed is that my multimeter reads 13-17v just with the black lead on 12u, not touched to the big board's G ??
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Can you post the model number or a photo of your meter?
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It's a klein mm400, read out all the voltages for when I built the regular crack just fine, got it only a couple days ago brand new
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The meter may need you to hit the Range button until it goes to auto or down to a low range where you can resolve something close to 0V.
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That is what I've been doing, I set the meter to volts then press range 4 times until it says 0V. Then I set it to MAX to get a reading that doesn't fluctuate all over the place when I touch the leads. Got my readings this exact way when I built without speedball. Without MAX it just reads 0-1V with 12u and G.
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12U didn't read 13-17V on my meters max mode on the regular crack voltage tests or any of the terminals that need voltage at 0 beforehand either if my memory serves me right.
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That is what I've been doing, I set the meter to volts then press range 4 times until it says 0V. Then I set it to MAX to get a reading that doesn't fluctuate all over the place when I touch the leads. Got my readings this exact way when I built without speedball. Without MAX it just reads 0-1V with 12u and G.
Is there a range that says "auto"? You should be able to measure 1.5V on a AA, AAA, C, or D battery as a test.
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Yes, I tried a brand new double a battery on auto and it reads 0.000V, I'm starting to suspect my meter is a $50 piece of brand new junk.
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If there's a Harbor Freight nearby, the cheap $7 meter they have there is more or less adequate for this kind of work, and the $23 meter is reasonably nice.
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Was the meter set to DC volts - parallel flat solid and flat dashed lines? I have a bunch of cheap meters that I use for doing lots of simultaneous measurements and they require a lot of button pushes to configure properly.
Don't use the "MAX" setting - it looks for and displays the maximum value measured. Great for detecting one-off voltage spikes, but not so good for basic voltage tests (and don;t use "MIN" either, for a similar reason). You mentioned that if not set to "MAX" the meter reads 0 to 1V at 12 - and 0 is what you're look for.
And make sure the meter has fresh batteries. I've gotten some crazy readings when using batteries that were only marginally low.
cheers, Derek
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OK idk if you believe me but I figured out the correct voltage mode before you posted lol. I also redid solder joints on some of the black leads. Here are my readings
OA - 110
OB - 112
G - 0
B+ - 204-210
Everything seemed OK, plugged in my phones and worked for about 30 seconds, then started getting distortion in left channel even with nothing playing. Not sure if it's related to my problem, but I did see voltage spikes on G a couple times while measuring it with my meter.
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Distortion is usually a loose wire.
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Left channel now doesn't have any sound :/
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No sound could be a loose wire/bad connection, or something else. Have any voltages changed?
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Voltages haven't changed, any connections in particular I should be looking at? Maybe one of the terminals is changing voltage only when I'm not checking lol
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No sound would have me looking for debris across the RCA jacks shorting them out, loose or broken wires going to or from the volume pot, or loose/broken wires going to and from the headphone jack. Many of the other problems that would cause a channel to drop would also make very noticeable voltage issues.
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I resoldered some more joints, checked voltages again. Now OB is getting 196V and B+ is getting 230, others didn't change and these two LEDS stopped lighting up (or maybe they were never lighting up?). Also looked at the RCAs and there doesn't seem to be any continuity between their underside soldered tips and the chassis. The pot seems ok and so does the headphone jack, I can take more pictures if it helps.
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One black wire on the heapdhone jack looks like it isn't captured by solder.
Is that OB on the big board or little board? I would guess the big board by your photos. I would suggest reflowing all the joints on the big board, giving a lot of extra heat to the center leg of the TIP50C. I would suggest leaving your soldering iron on that middle lug for at least ten seconds.
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I redid all the joints on the big board and reattached it, readings are
OA - 119
OB - 218
G - 0
B+ - 227
and the same two LEDs aren't lighting up :/
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There's a broken wire from the board to the socket, or a miswire from the board to the rest of the circuit, or there's still a bad solder joint on the board itself. The B+ being high and OB being high means that half of the board just isn't allowing half of the 6080 to draw current.
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I looked at the board and the wiring back to the circuit and I can't see anything obviously wrong. It seemed so close to working now I'm not sure what to do
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You have a solder bridge across one of the LEDs on the bottom of the board.
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Wym where? All I see is the oily looking residue from soldering, is that stuff conductive?
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Solder bridge, iffy joint, and leads to be trimmed.
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How's that? Good to go back into the circuit?
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On each leg of each TIP50 transistor, I would hold your soldering iron on there and count to ten, then move on to the next leg. You can do one leg of the A transistor, then a leg of the B transistor, then back to A, etc. switching off to keep the transistor from heating up too much.
It also looks like maybe one end of one of the 47K resistors needs some more heat and solder.
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OK, so I did all of that, put the leads on the board again, go to do resistance checks, then OB gives me around 4.6 megaohms, and OA doesn't read anything.
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As long as that's not close to 0, then you pass that resistance check.
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What about OA? It doesn't give any reading while the other one did give a reading on my meter.
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One side is reading 4,500,000 ohms and the other side is reading so high your meter can't determine what it is.
The manual says OA and OB on the big board should be several hundred thousand ohms at minimum.
I'm not seeing what the issue is here, I would move on to checking the voltages.
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OA - 120
OB - 221
G - 0
B+ 246
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Let's go back to pictures of the bottom of the board...
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Trying my best lol, this pcb soldering stuff isn't as easy as the stripping wires and soldering them to terminals sticking up ig...
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Can you send me a link to the solder and soldering iron you're using?
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I've been using this 60/40 rosin core radioshack solder that's been lying around in my garage forever throughout the whole amp, as for irons I've used this bluepoint soldering gun for about 95% of the time except for just recently with the pcbs I started using this weller iron (I like the soldering gun better).
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I would use the gun on your board. You can leave the LED joints alone, but use the gun on everything else.
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OK, reflowed with the gun put the board on again, resistance check, meter didn't read anything, voltage check
OA - 117
OB - 220
G - 0
B+ -226
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Well, at this point I would suggest sending it in for repair and I can fit a new board on it for you, or you can e-mail replacementparts to ask for a new board, or you can pull the LEDs and the two transistors on the bit that's not conducting and replace them.
Board rework isn't super easy though.
It's moderately probable that the big lump of solder that I saw bridging the connections on one of the LEDs would've required enough heat to melt the LED itself, and it may be damaged. Some meters have a diode check setting that can allow you to measure them, and they should show about 1.57V in one direction and nothing in the other.
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My meter does seem to have a diode check, not sure how to work it though. I'm not super eager to spend more $ to send it back for repair tbh especially having been so close to having everything working :-\
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Well, you can get some solder braid and wick the solder out of those joints. I would start with two new LEDs, then see what the results are before yanking out the transistors.
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I went ahead and replaced the big board and everything on it with new parts, did the tests and everything works now. Thanks