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Electro Harmonix Guitar Pedal, not fully functional

Ollie Elmes

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Hello,

Please see video


I have a soldering iron and a volt meter but not much of a clue as to where to start to try and get this pedal fully functional. You can hear the pedal is doing something to the tone but it's not firing on all cylinders.

If you look at the very last clip from 1.17, there are 2 metal things (technical term!) coming off the circular blue shape, one is connected to the board the other doesn't seem to go anywhere. Does this look right?

Any suggestions appreciated.

Thanks,

Ollie
 

betwixt

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Don't worry about the 'metal things' being broken. That's a potentiometer but using one leg and the middle one (other side of the blue knob) uses it as a variable resistor, it is a legitimate use and nothing is wrong.

That looks to be very 'home made' so I doubt a schematic is available. It is certainly repairable but with no schematic and limited test equipment it would be very difficult.

Brian.
 

Ollie Elmes

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Thanks Brian,

Good to have the potentiometer cleared up, I'll leave that alone then!

The soldering is very curvy shall we say, nothing like I've ever seen before. (not that i've seen that much)

I did have a look for a schematic diagram, with no joy.

What I don't understand is, everything seems to be soldered in place, everything looks as it should be but I guess there are many variables that can't be seen by eye.

Thanks again.

Ollie
 

c_mitra

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I cannot make out what is the disease, but I can suggest a very general antibiotic.

Just touch all the solder joints with the soldering iron; let the solder melt and solidify. No, I am not asking you to remove any component.

This will eliminate any loose or cold solder joints to clear up. You can also brush it with a used tooth brush (be gentle) to remove usual junk that might have accumulated.

Also look for any component that might have got overheated (dark color; soot on the board, leaky or bulging capacitors etc).

The input and output connectors may need a good dusting with the tooth brush.
 

Ollie Elmes

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Ok, wow, that's a lot of solder points but I'll give it a go and feedback. Thanks!
 

c_mitra

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I too cannot make out what is wrong; the approach therefore is necessarily brute-force.

But it should not be a laborious task; you need to touch up the solder joints with a hot and wet soldering iron. Each junction should take about 5-6 seconds.

As the system is working but noisy, it is possible that some component has partly failed; these are usually difficult to discover.

But there will be some change I hope, after the touch ups!
 

Ollie Elmes

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Thanks, yes, will try it tonight or over the weekend and report back.
 

Relayer

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Hello Ollie,
Would there be a chance that you could take some photos of the component side of
the guitar effects circuit board?
Thanx.
Regards,
Relayer
 

Ollie Elmes

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@Relayer I will get you a photo over the weekend.
@c_mitra I tried the soldering last night but no difference I'm afraid, sounded exactly the same.
 

Ollie Elmes

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A few more photos...the underside plus a couple of close ups of what looks a bit dodgy to my eye...
 

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Relayer

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Please refer to your modified picture below:

KxZAtc5.jpg


The IC with the red square seems to have been overheated. I'd say for a certainty is
identical to the other eight leg device.
The resistor shown within the blue box (4k7Ω) seems to have a hole on the gold band.
Could you please measure it.
Might be best for you to lift one leg of it for a more accurate measurement.
I've never seen transistors as shown with the green circles. This is a very old effects pedal,
I'd say made in around the 70's.
One of those two capacitors seems to have been overheated, shown by the red arrows.
It wouldn't hurt to replace them with a couple of modern ones.
Please let us know how you get on.
Regards,
Relayer
 

KlausST

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I've never seen transistors as shown with the green circles.
Don't know any part number...
but the white part most probably is ceramics and the black part is plastics compound

Klaus
 

betwixt

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That was quite a common package, especially for FETs in the 1970s and 80s. I think Toshiba used it quite a lot. Got some here somewhere in the cobwebs!

I'm not sure I would agree with Relayers diagnosis. From a small 9V battery it unlikely enough current could flow to overheat anything. I would think dried up electrolytic caps or open circuit high value resistors far more likely.

Brian.
 

Ollie Elmes

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Thanks for the feedback on the photo. So if I can find these replacement parts, I might be up and running?

I've attached some more photos, with a ruler in shot to give you a sense of scale.

@Relayer I'd say the resistor in the blue band is about 6mm

Thanks again!IMG_3649.JPGIMG_3647.JPG
 

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Relayer

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@Relayer I'd say the resistor in the blue band is about 6mm

I was meaning an ohms measurement, not it's length.

I'm not sure I would agree with Relayers diagnosis.

Might be a long stretch on my part, but having nearly all the markings on the IC almost
completely gone, I still find it suspect.
Passive components are much more robust than semiconductors, then I would consider
replacing the two eight leg operational amplifiers.
What have you got to lose? They shouldn't cost more than a few dollars each.
Regards,
Relayer
 

betwixt

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Let me have a look in my stocks - I'm fairly sure I have many (possibly hundreds) of 1458 op-amps and TL084s. If I can find them you are welcome to some to try if you can manage to solder them.

Brian.
 

Ollie Elmes

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@betwixt Thanks for offering to dig out the parts. Let me know if you find anything.
@Relayer As you say, what have I got to lose!
 

KlausST

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Hi,
but having nearly all the markings on the IC almost
completely gone, I still find it suspect.
the IC which is good visible shows "M745" on top left corner.
I´d say residuals of the other IC show the same. --> unlikely to be a different IC.

Klaus
 

betwixt

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sorry - been rushed off my feet for the last few days. I will look tomorrow for you.

I agree with Klaus, given the vintage of the board and what it does, the ICs are likely to be the same. The generic part number is 1458 (LM1458, uA1458, MC1458 depending on manufacturer, and there were many) but one is from a different batch to the other. The clue is the black discoloration of the pins, most manufacturers tin plate the pins, a few used silver plating and it is those that turn black after a few years. Functionally, it doesn't make any difference and the part of the pin covered with solder will be as good as new, only the exposed part turns black.

Brian.
 

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