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Old 12-06-2012, 04:19 PM   #41
sethasaurus
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Hey whoomit, how did you get on?
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Old 12-06-2012, 08:33 PM   #42
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Ah, I was waiting for you to get back to me. I forgot
You already had, damn! Will get back to work tomorrow
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Old 12-07-2012, 07:19 AM   #43
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Re-tested the transistors:

Code:
B C Tr1: 0.6 0 Tr2: 0.62 0 Tr3: 0.63 0 Tr4: 0.01 0 Tr5: 0.73 0 Tr6: 0 0


Tr6 did read something, but it dropped down to 0 very quickly, I think it read - 0.14 or something.

I'll check the soldering, then if that doesn't work I'll take it out and test it if I can.

Edit: Left it for a bit and checked it again. It came up -0.06, and dropped down to 0 in a few seconds.

Another Edit: Tested Tr6, and it's fine, time to try Tr5.
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Last edited by whoomit : 12-07-2012 at 08:10 AM.
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Old 12-07-2012, 08:15 AM   #44
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Okay, problem.

Tr5 checked out okay, but bhe conductive path has started to come off while I was removing the solder from the pins on it.
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Last edited by whoomit : 12-07-2012 at 08:18 AM.
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Old 12-07-2012, 10:36 AM   #45
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Try and minimise the heat you apply for desoldering. Sometimes the traces still peel anyway, depending on the quality of the pcb. I usually strip some wire and use the copper to make a new link where the old pcb trace was.
See how Tr4 & 6 check out. 1,2&3 should be ok.
Tr4 is the one that mutes the 'normal' stage (which is silent), so perhaps it has failed on or the one driving it has failed (Tr6).
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Old 12-07-2012, 10:43 AM   #46
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Already tested 6 and it came up fine. I'll take out 4 and test it.

I'm can't control how much heat I'm applying at the moment really as my soldering iron's a bit buggered.

Not looking forward to replacing the traces!
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Old 12-07-2012, 11:20 AM   #47
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Tr 4 is fine.
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Old 12-07-2012, 07:43 PM   #48
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OK I'm going to have to think a bit harder!
Do you actually get sound when the pedal is plugged in and the boost is on?

All I can think of right now is either:
- IC1 or IC2 is dead.
- R58 (on Effects send/receive) may be open circuit
- One of the wires to the board may be broken
- A pot or jack may have some corrosion and need cleaning.
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Old 12-09-2012, 02:16 PM   #49
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Yeah i do, just as quiet as when it's not pluggted in though.

Well, I Gordon suggested I test the ICs earlier in the thread, and here were the values I measured:

Code:
IC 1 IC 2 IC 3 Pin 3 -0.07 -0.06 0 Pin 4 -15.26 -15.41 -15.48 Pin 6 -0.07 0 0 Pin 8 15.22 15.44 15.44


The pots all appear fine, and I've already cleaned them all inside with contact cleaner. Will have a look at R58 and the jacks soon.
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Old 12-09-2012, 03:39 PM   #50
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Quote:
Originally Posted by sethasaurus
OK I'm going to have to think a bit harder!
Do you actually get sound when the pedal is plugged in and the boost is on?

All I can think of right now is either:
- IC1 or IC2 is dead.
- R58 (on Effects send/receive) may be open circuit
- One of the wires to the board may be broken
- A pot or jack may have some corrosion and need cleaning.

This was my first instinct, I'll actually get a TL072 out to you tomorrow you can try jam it in parallel for testing.

you have to get the 8 legs touching all of the legs on the one you're testing, but make sure the capacitors are discharged and don't touch it while it's on, there's a potential 30V on those legs that will **** your hand up.
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Old 12-09-2012, 04:16 PM   #51
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Thanks Gordon
Would there be a TL072 in an MG 15? I remembered that I have one sitting around, that I'm happy to dismantly for parts. It doesn't get used.

I'm going to try and get the pcb trace sorted tomorrow.
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Old 12-10-2012, 08:43 AM   #52
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For fixing the PCB traces am I best off using the individual strands from stranded wire or clipped legs from resistors etc.?
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Old 12-10-2012, 02:38 PM   #53
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I used to have a roll of tinned copper wire.
Resistor legs are ideal too.
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Old 12-10-2012, 02:54 PM   #54
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I'll use the legs then, got a whole bunch of clipped ones. Knew they'd come in handy someday.

I was going to get this done today, but then I had to go and work. Won't get it done tomorrow either. I'll see about doing it this evening if I have the patience
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Old 12-10-2012, 03:37 PM   #55
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Yep, it's a bugger having to work for money!
I think the MG15CD has a TL072 in it, but the other models use different op-amps.
The TL072s are cheap enough (less than a dollar) if you need to order some anyway.
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Old 12-19-2012, 09:02 AM   #56
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Right, finally got back to this.

Think I've fixed the PCB tracing, continuity test to see? Where from?

Edit: Just cracked open my MG to see if there were any ICs with the same code on them, but unfortunately not.

Nevermind, I was mistaken. Will take it out.
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Old 12-22-2012, 07:27 PM   #57
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I'm bumping this thread, but with good reason.

At first glance it probably looks like somebody had given me advice, and I haven't taken it. The last post is from 'asicsingy' according to the GB&C forum, but actually it's by me, so yeah...

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Old 12-22-2012, 09:10 PM   #58
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I don't understand your question about a continuity test.

You're at the stage where you're going to have to replace IC1 and 2 to see if that fixes it.
(Gordon's recommendation from before).

One method is to do a blanket replacement of semiconductors if they are cheap enough.
The other method is try and narrow down the fault. That's what I did by stepping you through the things I would check if I was doing it.
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Old 12-23-2012, 08:57 AM   #59
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Quote:
Originally Posted by sethasaurus
I don't understand your question about a continuity test.

Right enough, I never said where the PCB tracing that I replaced was! It's around the transistors that I removed and check, and put back in (Tr4, Tr5, and Tr6).

If I take my multimeter and put the black lead to the ground, where all should I be testing with the red lead around the transistors? Are there specific legs I should check, or just all of them?


Quote:
Originally Posted by sethasaurus
You're at the stage where you're going to have to replace IC1 and 2 to see if that fixes it.
(Gordon's recommendation from before).

Gordon was talking about placing it in parallel to check though, how do I do that? Or would I be best just taking them out and replacing them to see if it makes a difference?

Quote:
Originally Posted by sethasaurus
One method is to do a blanket replacement of semiconductors if they are cheap enough.
The other method is try and narrow down the fault. That's what I did by stepping you through the things I would check if I was doing it.

I'm not entirely certain what a semiconductor is, is that just a term for all the components?
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Old 12-23-2012, 05:12 PM   #60
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Quote:
Originally Posted by whoomit
Right enough, I never said where the PCB tracing that I replaced was! It's around the transistors that I removed and check, and put back in (Tr4, Tr5, and Tr6).

If I take my multimeter and put the black lead to the ground, where all should I be testing with the red lead around the transistors? Are there specific legs I should check, or just all of them?


There's no need to do a continuity test on a bit of wire you've just soldered in. As long as you joined the points that the trace connected originally, you're fine.

Quote:
Originally Posted by whoomit
Gordon was talking about placing it in parallel to check though, how do I do that? Or would I be best just taking them out and replacing them to see if it makes a difference?


I'm not entirely certain what a semiconductor is, is that just a term for all the components?


Well, I've never, ever done any repairs that way.
If you put a chip on top of a chip already in circuit, you change the circuit completely. For example, if the existing chip has a shorted output, then the good 'piggybacked' chip will just behave the same way - you won't know whether it is good or not, and you could possibly damage it (and still not know).

The TL072s are so cheap - just replace IC1 and 2. (Careful of those PCB traces )

Semiconductors - transistors, diodes, IC's, etc - basically anything that isn't a resistor, inductor or capacitor.

Last edited by sethasaurus : 12-23-2012 at 05:14 PM.
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