Build Your Own Clone Message Board

(Cross posting this from Madbean's hosted GrindCustoms forum because I know you all better.)

This Catch22 overdrive from GCFX functioned great when I briefly tested it; then I loaned it to a friend who said it cut out on him and smelled like burning. I opened it up and tested it. It still functions but does cut in and out almost like something is shorting out. And the charge pump (IC2) gets incredibly hot when plugged in (1Spot). I've reflowed the joints I can get at without removing the pots.

Anyone see anything?

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Scott

My band, Austin Hollow

A hot chip usually means a short somewhere.
C8 or 9 may have gone open, or perhaps something is happening under the socket. Check for continuity between all legs with both the IC in and out. There should be none, except between legs 1 and 8. leg 3 should have continuity to ground, but no others.
Try a different charge pump (IC2), they fry easily if they see voltages much over 10v. You should have -9v at leg 5 and +0 at 1 and 8 too.

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"Spud knows tone"

codtone.com

I fixed a Klone recently that had a short in one op amp drawing enough power to make the charge pump hot. Try swapping the op amp with a known good one and see if that helps.

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“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

I had a similar problem with mine recently. The op-amp chip had gone bad. I presumed it was the charge pump because it was hot. But after removing the charge pump from the socket and testing voltages, I found that I had 9V on more than one pin coming INTO the charge pump. No wonder it was getting so hot! I used 2272's in my original build. It turns out that the charge pump output is slightly over spec for that chip, and might have caused it to burn out after several months.

Well, first thing is...get rid of that One Spot!

I've had more than a few of my Klones come back with CP issues that were because of the One Spot.

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Granville Guitars - Guitar & Amplifier Repairs - Custom Effects Pedals - Hand Wound Pickups
http://www.granvilleguitars.com/

Scoot, why is that? My ones pot is consistently 9.2v and been a stable tool for years.

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They are cheap for a reason. Sustandard construction and components.

My customer Mike Zito blew out three charge pumps before we figured that one out.

It really depends on how hard you use them.

They are very unlikely to put up with any nonsense from your wall voltage.

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Granville Guitars - Guitar & Amplifier Repairs - Custom Effects Pedals - Hand Wound Pickups
http://www.granvilleguitars.com/

Changed the op amp, and now the charge pump doesn't get hot. But I'm still getting a splatting tone when engaged and static sound when turning the pots.

I took voltage readings on the charge pump:

1: 9.47
2: 0.12
3: 0.0
4: 0.26
5: 0.92
6: 0.0
7: 0.60
8: 9.47

The electrolytic caps don't seem to have continuity across the eyelets.

Before this last round of troubleshooting, I tested continuity on the socket pins of IC2 with the chip removed, and there was continuity between 1 and 8 as expected, but nowhere else.

I've been threatening to actually build an audio probe for years… maybe it's time.

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Scott

My band, Austin Hollow

IC2 voltages should be more like..
1. 9v
2. 4.5v
3. 0v
4. -4.5
5. -9v
6. 5v (not connected)
7. 7v (not connected)
8. 9v

I'd say that the problem is around there. Have you tried another one?
In this circuit it's not actually a charge pump, but providing a bi-polar power supply, +9 and -9v to give an18volt swing for more headroom. Getting -9v at pin 5 will likely solve your problem.

I'd swap out the IC, then C8 and 9, each time checking for the -9v...

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"Spud knows tone"

codtone.com

This is why I've switched to using TC1044SCPAs and a 12V Zener... but still tell my customers 9V regulated.

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Bikers have more fun that people do.

Free "open source" EagleCAD files: 99ZuluFX

Thanks, will see what I can do here. As I recall, I had to get the TC7660SCPA as a PIF because I couldn't find it from my usual vendors. But this info is helpful!

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Scott

My band, Austin Hollow

This.

These are far more robust. The symptoms suggest damage to your charge pump, they cycle internally very quickly, it's damaged and your power feed is breaking down, sagging or something similar.

I have a 1 spot and several charge pump/inverter pedals with no issues over a sustained period of usage

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To err is human, blaming someone else shows management potential

Hmm, is the TC1044SCPA a pin for pin replacement for the TC7660SCPA? I found I can get the latter from Mouser, but I'm always up for going with a better option.

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Scott

My band, Austin Hollow

A quick check of the data sheets of the pinouts will tell you that most likely. They usually also feature an example circuit for usage which will be almost, if not the same as used on your PCB, once again compare the schematics.

All this still leaves you with the question of what mortally wounded the pedal? The 1 spot, a goof by you, your pal doing something goofy (without realising it)?

I'm leaning more towards protection of circuits from both over volting and reverse polarity, despite clearly advising buyers of the polarity and type of plug etc, there are still folks who seem to just plug a pedal straight into whatever they are using to power other stuff, or those horrendous cheap daisy chain efforts.

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To err is human, blaming someone else shows management potential

This ended "almost" all of my customer issues as well.

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Well you guys were right: I replaced IC2, and all is well. (Thanks for the target voltages, Ben!)

Once again I'm glad to have this great community that helps and teaches.

(By the way, the pinouts on these two charge pumps do match, and I ended up using the one you guys prefer.)

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Scott

My band, Austin Hollow