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whoomit
Join date: Jul 2006
1,492 IQ
#42
Ah, I was waiting for you to get back to me. I forgot
You already had, damn! Will get back to work tomorrow
whoomit
Join date: Jul 2006
1,492 IQ
#43
Re-tested the transistors:

     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.
Last edited by whoomit at Dec 7, 2012,
whoomit
Join date: Jul 2006
1,492 IQ
#44
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.
Last edited by whoomit at Dec 7, 2012,
sethasaurus
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Join date: Nov 2012
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#45
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).
whoomit
Join date: Jul 2006
1,492 IQ
#46
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!
sethasaurus
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Join date: Nov 2012
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#48
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.
whoomit
Join date: Jul 2006
1,492 IQ
#49
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:

         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.
GABarrie
Call me Gordon
Join date: May 2011
1,073 IQ
#50
Quote 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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whoomit
Join date: Jul 2006
1,492 IQ
#51
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.
whoomit
Join date: Jul 2006
1,492 IQ
#52
For fixing the PCB traces am I best off using the individual strands from stranded wire or clipped legs from resistors etc.?
sethasaurus
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Join date: Nov 2012
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#53
I used to have a roll of tinned copper wire.
Resistor legs are ideal too.
whoomit
Join date: Jul 2006
1,492 IQ
#54
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
sethasaurus
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Join date: Nov 2012
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#55
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.
whoomit
Join date: Jul 2006
1,492 IQ
#56
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.
Last edited by whoomit at Dec 19, 2012,
whoomit
Join date: Jul 2006
1,492 IQ
#57
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...

sethasaurus
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Join date: Nov 2012
111 IQ
#58
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.
whoomit
Join date: Jul 2006
1,492 IQ
#59
Quote 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 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 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?
sethasaurus
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Join date: Nov 2012
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#60
Quote 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 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 at Dec 23, 2012,
whoomit
Join date: Jul 2006
1,492 IQ
#61
Right cheers.

I'll replace one of the TL072s tomorrow and see if it makes a difference. If not then I'll try the other one and get back.

PCB traces should be okay now, I've found my low-wattage soldering iron

I'll report back tomorrow!
whoomit
Join date: Jul 2006
1,492 IQ
#62
Okay, so here's where I'm at at the moment.

I couldn't take the IC out of the MG15 as I couldn't find any solder wick anywhere. Then I just so happened to get a solder vacuum for Christmas from my brother, so game was back on!

I removed the good TL072 from my MG, and put it in place of IC1. That made no difference, and now I've removed IC2 but I've snapped the legs on my other TL072 so I'll have to wait for some more to arrive.

In the mean time I'll be trying to get my PP-18 up and running. Seems to be something wrong with it too. Dammit!
whoomit
Join date: Jul 2006
1,492 IQ
#63
Turns out my footswitch doesn't work, which is why the boost is stuck on when I plug it in. Will be making a new one soon, when the parts arrive.
whoomit
Join date: Jul 2006
1,492 IQ
#64
Okay. I've swapped IC1 and IC2.

Since putting in the new IC2 there's no sound, unless I've got the footswitch plugged in (boost on). Are you sure TL072s were the right opamp?
GABarrie
Call me Gordon
Join date: May 2011
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#65
Quote by sethasaurus
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).

I never do repairs that way but it's a first step for testing without having to mess with soldering, if the chip has just died the parallel one picks up the slack and I know to replace it, if it doesn't make any difference then I move on with other diagnostic methods.
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GABarrie
Call me Gordon
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#66
Quote by whoomit
Okay. I've swapped IC1 and IC2.

Since putting in the new IC2 there's no sound, unless I've got the footswitch plugged in (boost on). Are you sure TL072s were the right opamp?

TL072s are the right opamp for it btw
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whoomit
Join date: Jul 2006
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#67
Quote by GABarrie
TL072s are the right opamp for it btw

I swapped them out for MC1458s, but I'll swap them back before I send it to you
GABarrie
Call me Gordon
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#68
SERIAL #12!?

This is probably the oldest surviving 5213 in the country, you lucky bastard

Looks beautiful, if you'd sent the cab too you may not have gotten it back, haha
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