Bottlehead Forum
Bottlehead Kits => Legacy Kit Products => Stereomour => Topic started by: funandfunny20 on March 05, 2014, 05:29:52 PM
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Hey Guys & Gals,
I finished my Stereomour this past weekend. I stayed up way to late…but it was all worth it—such a fun couple of days.
Everything sounded great and was working fine until last night. After about a half-hour of warm-up, the left channel starts to crackle/pop/hiss/distort. I swapped the tubes, but the problem still persists on the left side. I haven't measured anything since the problem started last night…I'll try to take some measurements before I go to bed.
Is it likely a bad resistor or capacitor?
The noises are not effected by volume. They're loud regardless.
Please advise!
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This is probably a funky solder joint. Voltage measurements will be very helpful.
-PB
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Here are the voltage measurements. T2 and OB are the problems….
“HV+†Settled at 400 and 398
T 1: 369
T 2: Only 3
T 3: 0
T 4: 0
T 5: 60
T 6-10: 0
T 11: 59
T 12: 0
T 13: 0
T 14: 218
T 15: 364
T 16: 60
T 17: 395
T 18: 0
T 19: 394
T 20: 60
A1: 60
A2: 365
A3: 0
A4: 60
C1: 60
C2: 358
C3: 0
C4: 60
IA: 388
IB: 380
OA: 217
OB:1
kreg (on OA/OB side): 0.8
kreg (on IA/IB side): 2.5
both regs: 0
From what I can figure, it looks like either the film cap itself, or some of the red-wire leading to it, aren't soldered properly.
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You'll want to resolder the center leg of the MJE5431A on the B side.
Also make sure the wires leaving Kreg go to pins 3 and 8 on the 9 pin socket.
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Well, I think i really messed things up…I think I got solder between OB and OA…because it started to smoke from in-between the two…now my board is black between them.
Suggestions?
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I've inspected the board…there is no solder between OA and OB….but it is sparking.
What might cause this?
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Here are some photos of the board:
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What should I do now?
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That black carbon may be forming a conductive path. You might try scraping it away with a sharp knife point or small screwdriver. you need to be pretty through and get down to clean board or it will arc over again. Or as long as there no trace on the underside of the board you could take a hacksaw blade and cut a slit between the two connections until you get past the burnt area...John
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Post any voltages that you have that are not consistent with the manual.
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I got all the carbon off and now the board at least doesn't spark!
While doing this, and also going over the manuel again, I noticed that I had the both tube sockets incorrectly installed…now the sockets are correctly installed. However, now all my resistance checks are way low. For example, A1, A4, C1, and C4 are only reading .6, not 1.2. A3 and C3 are out of spec as well. Terminal 1 and 15 don't read anything.
What have I messed up now?
I feel like a complete idiot….apologies in advance.
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While doing this, and also going over the manual again, I noticed that I had the both tube sockets incorrectly installed…now the sockets are correctly installed. However, now all my resistance checks are way low. For example, A1, A4, C1, and C4 are only reading .6, not 1.2. A3 and C3 are out of spec as well. Terminal 1 and 15 don't read anything.
That can be a pretty grievous error...
I would try a fairly brief voltage test to see what things look like, it's entirely possible that having the 4 pin sockets backwards roasted your 2A3's. If you measure the resistance between the fatter pins of the tubes (out of the sockets, just in your hand), what do you get?
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Yeah…that's what I am afraid of…
The tubes jump all over the place, but then after about 5 seconds finally settle at zero.
I just did a quick voltage test—doesn't look good. To make sure I didn't break anything, I only took a couple of readings:
HV+†0
A1: 0
A2: 0
A3: 0
A4: 0
C1: 0
C2: 0
C3: 0
C4: 0
both regs: 0
I think I should just pay the $125 and have you guys fix this.
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Oh, and I forgot to mention that the two LEDs closet to the output transformer are not lighting up.
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You could do that, but I'm pretty sure that you have a blown fuse.
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So I checked the resistance of the fuse, and it jumps all over the place, eventually settling at zero. I'm assuming it is not fried since I'm getting some reading, is that correct?
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Make sure you have good contact of the fuse ends and the test leads. I often rub the probes against each other to clear any oils that might be on them, and then rub the probes against the ends of the fuse to make sure there is nothing interfereing with the metal to metal contact.
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Hey Doc,
I just did what you said and while meter does jump up slightly, it almost immediately settles at 0. I'm going to make a run to radioshack shortly to get alligator leads and new fuse.
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Clip leads are a good idea. It sounds like the fuse is probably OK, but a new one is cheap insurance.
If the new fuse doesn't bring things back to life the next step is to make sure the power switch is working. WITH THE AMP UNPLUGGED use your new clip leads to clip a test lead to each terminal on the power switch then measure the resistance when you throw the switch back and forth. In one direction it should be overlimit and in the other it should read close to zero ohms. If it reads overlimit on both settings it needs to be replaced.
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Okay, so the Radio Shack near me doesn't carry 1.5a GMA slow blow. Only fast-blow. I'm assuming that matters, right?
As far as the power switch goes, it does OL when switched, and it is at zero when flipped back.
I did some resistance checks, and A4, A1, C4, C1, and all the other points that are supposed to read 1.2k Ohms, only read .5k Ohms.
Does that help with anything?
Sorry for all the dumb questions!
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That 1.2K is the fat resistors on each side of the driver socket. See page 66 of the manual for a picture. Are they the right values (1.6K and 4.7K)?
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Got new fuses, but I am still not getting any readings. Except, an odd reading is -reg, which is NOT 0—it reads .7 or something like that.
Just to cover my bases, the larger holes of the tube sockets are closest to the hum pots, right?
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I also checked the resistors. As far as I can tell, they are correct. I have them exactly like they are in the pictures, including the direction of the words.
The most confusing part of all of this is that the amp worked (and sounded good) for almost two days…
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Any ideas?
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If the 1.2K resistance (1600 parallel 4700) is really 500 ohms, then it is being shunted by something. The obvious candidate is the bypass caps on the PSU board. This could happen if they are in backwards. You can disconnect the wire that goes into the board terminals marked "K" and then measure the resistance again to test this theory.
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Removed both wires from the k terminals and I'm still getting the same results: A4, A1, C4, C1, and all the other points that are supposed to read 1.2k Ohms, only read .5k Ohms.
Any other suggestions? I'm thinking about just rebuilding everything. Is that a plan worth pursuing?
I'll attach some photos in a couple of minutes.
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Here are some photos.
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Sorry to say this, but it's time to unsolder and detach one end of each of the 166K and 4.7K white resistors and measure each one by itself to determine which one(s) are actually not the right value.
It might be a good idea to check your meter with some other resistors to be sure the meter is OK and this is a real problem, not a flat battery or something! Try R1 and R2 on the C4S board, they can be measured without removing them.
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Do you have your meter set on a megohm scale, perchance? Meters are notoriously inaccurate if set at high ranges to read low values.
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I am going to go ahead and concur that there is probably a meter issue here.
If A1/A4 and C1/C4 all measure around 60V DC, then you're not going to have 500 Ohms to ground from those pins.
It would be helpful to see a shot of your power supply board, as there may well be a cap in backwards.
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Man….turns out my multimeter was terrible.
Got a decent one from radioshack and everything looks good…except OB and terminal 2 are only at about 70.
Also, R2 (the one closest to the transformer), flashed a couple of times. And my LEDs on that side do not light up.
What should i try next?
btw, Thank you Doc, Paul, and Paul!
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Flashing could be a sign of a funky solder joint, I'd start there.
Does the ~70V reading persist after the funky flashing? Is the flashing initiated by you poking in there with the meter?
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Okay, re-soldered the R2 and now no flashing.
The voltage on T2 and OB still settles at 70v.
Is it bad to try it with speakers?
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OB at 70v means the 431 in the driver cathode on that side is shorted. You can test voltage at kreg; they should beoth be 2.5v but I suspect one of them is at 0 volts. Could be a short at the tube socket or on the PC board.
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Both Kregs are actually 2.5.
I'll inspect the socket and the 431 right now. Could the carbon from the flex (between OB and IB) cause the short? I cleaned it off pretty good and it no longer sparks.
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Here is a shot of the PSB.
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I've removed the PC board. A simple resistance test between OB and IB yield 20.0. Whereas, a resistance test on IA and IB yields 0.0.
Does that help with anything?
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All my soldering looks good. Just in case, I re-heated all three joints of the troubled 431.
Should I re-install the PC board and test the voltages again, or are there any other tests I should try before?
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I checked the resistance of R1 (on the side where the LEDs are out) and it's only showing 4.3, whereas the other one is reading 237.0.
Does that mean it's fried? This happens to be the same resistor that was flashing…
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Yeah, that's it. I can't imagine how it could have flashed, the current is small, but if it doesn't read 237 (or very close) it's toast and could easily explain the voltage reading.
There's no way to say whether replacing it will solve the problem, or whether some other bits may have been fried. It could be interesting to try - you can probably find a 240 ohm at RatShack or something locally - but I'd say the best bet it to get a replacement board and stuffin's.
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Thanks Paul. I think I'd rather just get new stuffin' and the board…
Should I just order the S.E.X. C4S upgrade kit?
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Got a new PC board (and parts), soldered, and installed.
The only resistance readings I have that are out of spec are: Terminal 20 is 1.4 instead of 1.2; C3 settles at 395; and terminal 12 settles at 387.
Is this a major problem?
Suggestions?
Thanks in advance!
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Did the voltage tests:
Here are the issues. 1) Kreg on the A side is only at .9v. 2) the LED closest to IB/OB is not lighting up. I re-soldered it, but to no avail…still not glowing.
What should I check now?
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I again, tried soldering the LED closest to OB/IB, and it worked! Did my voltage tests and everything sounded good..for five minutes before the RIGHT channel made this terrible loud popping/crackling noise.
I turned over the amp and started taking measurements again. After the amped is turned on, all four LEDs glow as they should. After about 10 seconds, I noticed that the LED closest to OB/IB is starts glowing way brighter than the other two on the side closest to the volume knob. And, also, the LED closest to the transformer and on the A side goes completely.
I performed all voltage measurements again this morning and everything is within spec, except for OB is at 374 instead of 165-220.
Both kregs are at 2.5.
Terminal 4 22.;
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Does anybody have any suggestions?
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I would triple check the 220 Ohm stoppers, you may have a broken one.
To be safe, you can replace them with easily sources carbon film resistors between 10 and 1000 ohms of whatever wattage you happen to find.
PB
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Hello!
I tested the resistors and both measured 220 and 230 respectively. This leads me to believe that they are no burnt out.
Any other suggestions?
Thanks….sorry for all the bother.
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Just tried another resistance check—terminal 14 reads 0.
Any ideas as to what I should check next?
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If terminal 14 reads 0 Ohms, then you'll get no left channel.
If terminal 14 reads 0 Ohms, then OA will be 0V.
I would suspect a wiring error at the 9 pin socket, or contact between pin 6 on the 9 pin socket and pin 5, or potentially contact between pins 6 and 7 (less likely).
-PB
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Okay,
Just got home a measured the amps…there are a couple of odd measurements. The amp's right channel currently crackles/distorts like a bad tube. So, I switched the tubes and the problem still persists on the same side.
Resistance:
T1 *; T2 *; T3 0; T4 248.4; T5 1.406; T6 0; T7 107k; T8 0; T9 97k; T10 0; T11 1.64; T12 248; T13 0; T14 *; T15 *; T16 1.18; T17 *; T18 0; T19 *; T20 1.18; A1 1.19; A2 *; A3 248; A4 1.19; C1 1.4; C2 *; C3 248; C4 1.4
The one's out of spec are C1 AND C4.
Voltage:
HV+ 398;
T1 370; T2 195; T3 0; T4 fluctuates around 0; T5 61; T6 0; T7 0; T8 0; T9 0; T10 0; T11 60; T12 fluctuates around 24.0; T13 0; T14 220; T15 369; T16 60; T17 398; T18 0; T19 398; T20 60; A1 61; A2 368; A3 fluctuates around 30.0; A4 62; C1 61; C2 370; C3 fluctuates around 40.0; C4 61; IA 399; IB 399; OA 199; OB 220; KREGS 2.48; -regs 0.
T1 *; T2 *; T3 0; T4 248.4; T5 1.406; T6 0; T7 107k; T8 0; T9 97k; T10 0; T11 1.64; T12 248; T13 0; T14 *; T15 *; T16 1.18; T17 *; T18 0; T19 *; T20 1.18; A1 1.19; A2 *; A3 248; A4 1.19; C1 1.4; C2 *; C3 248; C4 1.4
What do you guys think?
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I think you may have a bad solder joint somewhere in the right channel side. Try reheating the connection associated with the right channel 2A3 and wires from the 12AT7 that go to that 2A3.
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Thanks Doc…it appears the issue is solved—the amp is working!
However, I'm slightly skeptical of my work, so I'll post back later if the amp stays working tonight and tomorrow. Crossing my fingers.
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So, I'm still having issues.
About every couple of minutes the amp pops and cracks loudly on the right channel. When you tap the amp, it pops/cracks.
This is definitely a sign of a loose solder joint somewhere, correct?
I've resoldered everything associated with the right's socket. Meaning, A1-4, Terminals 1-5 have all been resoldered. I know it's a definite shot in the dark, but should I resolder any other areas of the amp? I feel like I've thoroughly gone through the C4S board.
Any help would be greatly appreciated.
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About every couple of minutes the amp pops and cracks loudly on the right channel. When you tap the amp, it pops/cracks.
This is definitely a sign of a loose solder joint somewhere, correct?
Yeah, you're spot on!
Run it with a cheap speaker hooked up to it, then start gently poking and prodding with a wooden chopstick to determine where the funky joint is. (It will force a pop when you it it)
Do not hesitate to poke the transistors on the C4S board, one of them may be the culprit as well.
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I see Peebs was typing at the same time -
Yeah if you have eliminated a tube as the cause it's most likely that there is a connection that is getting flaky as the amp warms up. That would have me looking for two wires that might be a little too close together and making contact when they expand as they get warm, or a wire soldered thru a terminal that might not have a really smooth fillet of solder between the wire and the terminal. Sometimes a joint that looks like that actually has a layer of flux inside the joint that is breaking the continuity.
Just as a general example a very nice customer came by this week with a very nicely built Crack. All voltages were good and LEDs lit, but he was only getting sound from one channel. It turned out that tucked under one of the Speedball boards there was a wire with the insulation pulled back a little more than average, and it was just barely brushing the terminal next to the one it was soldered to. It took me a couple of tries to find it by poking around with an unsharpened pencil. When I touch the wire or the things connected to it it made some gnarly crackles (which is why we troubleshoot with $20 headphones!). I reshaped it a bit to make sure it wouldn't touch anymore and we had two channels playing.