? Overloaded Auto Chromatic Tuner

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Alec S. 19 years ago

Hi,

I have a Matrix auto chromatic tuner-to tune instruments-model SR-4000.

A while back I killed it by-accidentally, I swear!-plugging in a power cord which was set to a few volts too high (12v instead of 9v) backwards (reversed polarity).

I would like to fix it. I would like to diagnose the problem and if I'm lucky repair it (I assume it's a dead component that needs to be replaced.)

While I am no electronics expert, I am also not a novice. I have repaired computer hardware (and built a few parts of my own), and even our home's wiring (although that's really just dangerous, not complex.)

I've got a digital multimeter, variable power supply, all kinds of wires, alligator clips, etc, hopefully pretty much any tools I might need. I've also got a large box full of electronic part potpourri that I got from various places including a supplier a long time ago and from various electronic devices I've cannibalized.

I have scanned the circuit board and they can be found here:

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I've tried running a couple of small tests, but I don't really know how to test something like this. For example, I'm not certain how to test if a transistor is good (I've got an idea but I'd rather hear from experienced people), or a quick connectivity test reveals nothing useful since pretty much everything seems to be connected to everything else, and testing for power returns all kinds of variable voltages that tell me nothing.

Does anyone have any tips or advice (or maybe a complete walkthrough?) on how to test and repair this?

Thanks a lot!

Alec S.

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James Sweet 19 years ago

It doesn't look like there's any regulator or protective circuitry on the power input, I wouldn't be surprised if the reverse polarity killed the microcontroller or whatever that large Intel chip is.

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Alec S. 19 years ago

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Dave 19 years ago

Gee, maybe next time you can look at the site before you make some dickheaded un-informed comment about it.

It's consumer-oriented. Yes, it has hooks to search engines in online parts catalogs of all the major distributors. Would YOU rather search them all individually?

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William R. Walsh 19 years ago

Hi!

It's actually an 80C51 microcontroller. If it is fried, you'll not only have to replace it, but also the code that was programmed into it. Finding another 80(C)51 isn't going to be so bad. It's getting the code that makes it run that will be the hard part. You'd almost have to find another example of a working unit and try to get the code out of it somehow.

Have you tried the manufacturer to see if they would repair it?

William

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Alec S. 19 years ago

The code is to identify an input frequency. It's an instrument tuner, so the code is pretty important.

No, it's really old and would probably cost much, much more to have professionally repaired than to buy a new one. Part of why I want to repair it myself (besides that I'd rather not spend money I don't have) is to do an electronics project since I haven't done one in a while. Also, I feel awful that I wasted a perfectly good thing, and would like to alleviate that feeling.

Alec S.

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James Sweet 19 years ago

If the chip is bad you could probably write some code for an AVR or PIC to accomplish the same thing, it can't be too terribly complex.

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stratus46 19 years ago

Alec S. wrote: > Hi, >

1: The 80C51 is a pre-programmed microcontroller. Tektronix used bugs like this in the 1730/1/5 scopes. The point is they didn't set any of the protection features so I read out the program from a working unit, programmed it into an 8751 (actually 8752 but the concept is the same) and brought the other scope back to life. The two-fold hitch is you need a programmer and a working chip AND the protection bits NOT set.

2: Someone else noted a 78L05 regulator that may have failed. There certainly is some sort of regulator as the 8051 family is 5 volts and will let the magic smoke out with 9 volts. There might be a protection diode on the power input to protect just this mode. If that failed, an ohm meter on the power input would read nearly 0.

My bet is the processor is still OK and repairing the regulator(s) will bring it back.

GG

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Alec S. 19 years ago

That's what I'm hoping. Can you advise me on how to test the regulator(s)? (I'm not even sure which one it is.)

Thanks.

Alec S.

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? Overloaded Auto Chromatic Tuner

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