Dead Boss CS-3

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sadrew
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Post by sadrew »

Hi there,

I have on my bench a Boss CS-3 compressor which is completely dead.
It's one of the first versions, with the DBX 1252 VCA.
It's supposed to sound very good (actually I've never tried it in person), so I would bring it back to life.
Below I attached the original schematic and service manual, looking for help

I have started to debug it with a voltmeter and audio probe, and here it's what I've discovered so far:

- The pedal doesn't pass audio signal, neither the status led powers up

- I've checked the path with the audio probe, starting from the input, and the signal gets lost at IC1 pin 3, just the first one

- I've started measuring voltage coming out of the DC jack. The +9V rail seems to be ok, but after the voltage divider (R2/R28) I read 5.8V instead of the correct 4.5V.

- Another thing that seems very strange to me, but I don't understand what could be the cause of this problem:

If I measure the voltage between the two poles on the DC jack i read the actual supply voltage, 8.9V.
But if I read between the DC jack positive and the case (which is connected to ground too) i read 6.15V.
More, if I measure voltage between the case and the DC jack negative pole, I read 2.79V

My guess is that the pedal has been feed with a wrong power supply, which has damaged some components, but I don't know which ones.

Of course, I can provide all the voltages measurements you may need for understanding which components are fault. Just ask what you need.

I think that maybe replacing all the ICs, diodes, transistors and electrolytics would solve the problem, but some of the components are hard to find, so I am asking your help to spot on the problem.

Any help is highly appreciated

Ciao!
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blackbunny
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Post by blackbunny »

sadrew wrote:My guess is that the pedal has been feed with a wrong power supply, which has damaged some components, but I don't know which ones.

Of course, I can provide all the voltages measurements you may need for understanding which components are fault. Just ask what you need.

I think that maybe replacing all the ICs, diodes, transistors and electrolytics would solve the problem, but some of the components are hard to find, so I am asking your help to spot on the problem.

Any help is highly appreciated
Have you had any success with this yet? I can give you a few tips on repairing Boss pedals if you are still needing.

Most Boss problems come from incorrect power supplies, so I always test & replace the components in the DC supply first...that fixes over 90% of all problems.

In the CS-3, replace D1 protection diode (a 1N4148 will do), C1 (100 uF / 16V or 25V if available), C3 (47uF 6.3V, 10 or 16V is better), D10 (1N4148 or Schottky such as 1N5818/5819) and possibly IC1.

Test DC voltage at pin 5 and pin 7 of IC1 (M5218L inline IC), if it's around 4.2-4.5VDC the IC is probably OK.
If the DC voltage is low at pins 5 & 7, the IC may be shot.

The M5218L IC's can be hard to find; you may have to order a couple from Small Bear.

You may have worked through these steps already. How far have you got?

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Mutkis
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Post by Mutkis »

Hello!

I am new on this Forum and I have very little of experience in electronics and less when it comes to problem solving. I have a similar problem with my Cs-3. I measured Voltages with multimeter and the readings were something else than supposed to. I also measured the protection diode. What should the voltage be on the minus side of the diode, reading on my multimeter is 0V this can't be ok, can it?

And sorry if it is not correct borrow this topic rather than create a new one, on another forum it is adviced to write similar problems under samekind of topics.

Yours Faithfully,

Mutkis

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blackbunny
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Post by blackbunny »

Mutkis wrote:I also measured the protection diode. What should the voltage be on the minus side of the diode, reading on my multimeter is 0V this can't be ok, can it?
The voltage on the minus side of D1 protection diode should be 0v, and on the positive side should be the DC supply or battery voltage of around 9v.

With a plug inserted into the input jack, measure the voltage drop across the series protection diode D10 (should be 0.5-0.6 vDC) and R32 / 220 ohm resistor (0.2-0.3vDC). If the voltages are 2x or higher, the circuit is drawing way too much current.

Replace the diodes and electro capacitors as described in my previous post and test again. If the voltage drop across D10 and R32 is still too high, the IC's may be damaged and should be replaced.

If the voltage drop across D10 and R32 are only slightly high, try replacing R32 with a 47 ohm resistor and see if the circuit works.

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fenderme
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Post by fenderme »

I see you say 90% of problems are due to power supply issues.
I had not realised that I had a faulty power supply, and now have a problem with my CS3!
It still works but now has a sort of whistle sound when the sustain or level is turned up, so hoping nothing too bad.
You seam to suggest the components close to the power are possibly the faulty parts, but I would appreciate any assistance in repairing it rather than throwing it away.
I have schematics and a multimeter, a bit of electrical knowledge.
Sadly before I noticed it had affected the CS3 it blew my Jeykll & Hyde pedal [smilie=a_blue.gif]

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