BOSS CH-1 LED turns on but no effects signal

[tgeucihtnairk]

Hello everybody,

the title says it all...

When i turn on the CH-1 the LED will turn on, but there is only the clean sound coming out of the pedal, no chorus effect.

I know, the first advide you will give me is to turn up the effects level but i've done that already i used that pedal for some years now.

Do you have any idea what might be broken there and how i could fix it? Any advice is appreciated.

I wanted to sell this pedal now cause i received my made in Japan CE-2 yesterday. But for a broken pedal i won't get that much money i suspect

Thanks for your help in advance!!

[tekhed7]

Referring to the schematic, if Q4 is bad (2SC1605A? hard to read), it won't alternately switch the Wet-sound- (Q2) & dry-sound- (Q1) passing FETs on & off properly. You may also have a defective FET at Q2. (Both FETs are standard #K30A's)
See if you can verify the 'bucket brigade' delay chip IC2 (MN3007) is doing it's thing by scoping or signal tracing (listening to) the emitter lead of the chip's "output Lo-pass filter amp"- Q10, a 2SC2240. If it's dry THERE, you probably have a bad MN3007.
Audio goes from that emitter lead thru the 'EQ' pot, thru the 1st 1/2 of IC5 (in 3 & out 1) thru the E.LEVEL pot, thru C40, R50, thru Q2 (when EFX 'ON') & into the 2nd 1/2 of IC5 & out pin 7 heading for the output jack. Good luck!
{e-mail me 4 the schem in PDF if need be} -M.S.

[tgeucihtnairk]

*SYSTEM OVERLOAD*

I think I'll sell it as broken. I don't have a clue what I have to do now, hahahaha

and on Q4 it says C945P19YC in my pedal

But thanks for your help!!

If anybody can give me something like a step-by-step instruction on where I have to check what I miiiiight give it a try. Otherwise I'll sell it as a broken pedal on ebay just in case anybody's interested

[tekhed7]

sorry there! I'm new to this forum & figured you'd had experience tracing thru pedals like this. The issue is most likely a bad MN3007 or a bad FET, but w/o using a scope to trace a test tone or guitar strums thru it, the troubleshooting procedure gets involved.

You can start by measuring the voltages on Q4 and verify the collector jumps between about a volt & 8 volts or so. This means it's "telling" the J30A FETs (Q1 & Q2) to alternately let thru the dry & the wet sound, but w/o an audio signal tracer or oscilloscope to verify what's really happening- and a schematic to trace it thru- it's best to sell it as-is, or give it to a local shop for an "estimate".

[tgeucihtnairk]

Ok, then I'm outta here. I neither have an audio signal tracer nor an oscilloscope, so i'll put it on ebay within the next few days. It's ebay Germany if anybody should be interested in it.

Thanks a lot for trying to help me anyway

[Mark Hammer]

STOP.

A tiny bit of theory before I tell you how to fix it.

The MN3007 chip is the one that produces the time delay needed to create a chorus effect. The MN3007 consists of a great many teeny tiny capacitors and FET transistors. The FETs serve as little gates or switches that let current pass from one cap to another when instructed to do so by a clock pulse coming from the MN3101 chip. The time delay is produced by the stage-to-stage transfer of the current stored in one capacitor to the next in line then the next in line and so on.

The whole process, however, requires that your guitar signal "ride" on a steady DC voltage. Think of it like a kid trying to get onto a carnival ride that has a height restriction, so he puts on platform shoes to be tall. That DC voltage is your signal's platform shoes.

The DC voltage (called the "bias") is derived from the battery supply. A trimpot is used to divide down the battery supply voltage, much like a volume control would, so that it is some fraction of the 9v the battery puts out.

When the bias is bang on, the chip will pass signal and produce glorious delay. When the bias is a little high or a little low, you'll hear sound from it, but slightly distorted and not full volume. A little higher or lower than that and it will be significantly lower in volume and quite distorted, until finally a little higher or lower than that and the MN3007 simply has no output. The trimpot is normally set properly at the factory, but there are any number of reasons why it could be dislodged enough for the delay chip to sit there doing nothing.

In the case of the CH-1, however, it would appear that Boss elected to use fixed resistors instead of a trimpot, probably to reduce production costs. What I'm wondering is whether your battery supply is too low, and the resistor circuit is simply not providing a decent bias voltage. What does the battery measure?

The other thing is that the CH-1 has two output jacks, and is wired such that inserting something in jack 2 results in the delay signal being cancelled at jack 1, so that you can have a "stereo" ouput. Is there any possibility that:

a) the 2nd jack is buggered up so that it "thinks" you have something plugged into it?

b) The FET that does the switching - a 2SK30ATM...or K30A - is buggered, meaning that the wet signal is there but simply doesn't reach the A output?

You can see if possibility b is true by soldering a little wire from the 33k resistor labelled R50 (orange-orange-orange) to pin 6 of the chip labelled U5 or IC5. That will bypass the FET so that the signal cannot be switched off. If te FET is buggered, then this should restore chorus sound.

We'll take it from there.

[tgeucihtnairk]

Ok, now that's interesting

As a power supply I'm not using a battery. I'm running it with an external power supply that is working fine with all the other BOSS pedals that i have. So I don't believe that's a problem.

I always had a short plastic plug in jack 2 so that I wouldn't put any cable in this one by mistake. It always worked fine for me. But I will try connecting two of my amps in stereo to see what happens.

As for the soldering: I'm currently at university studying for an exam on wednesday so i'll check that after my exam 'cause I don't really have the time for that now.

But thanks a lot for your reply!!

In case there are some grammar or spelling mistakes: English isn't my mother tongue so please don't kill me for that

[Mark Hammer]

Your English is excellent. I hope you write as well on your exam!

[tgeucihtnairk]

I'm glad to hear that

I connected my CH-1 in stereo now:

With the effect turned off I get a perfect clean sound on both outputs.
But when I turn it on output B is still clean and on output A there is some weird sound.
It's like a popping sound somehow, no guitar signal. And i can change that sound by turning the knobs. They're all working the way they're supposed to. So I can make it louder, change the EQ and so on.

Hope that helps somehow

[Mark Hammer]

It does help. It tells me the switching system is generally AOK.

Did you try bypassing the switching JFET for the wet signal?

[tgeucihtnairk]

I didn't try that yet.

It's a chip with 8 pins in a row, right? How do I know which pin of the chip is number 6? From which side do I count?

Is it important to which "side" of the resistor I solder the wire?

The resistor labeled R50 isn't orange-orange-orange on my PCB, it's red-white-orange, 29k.

[Mark Hammer]

No. We're talking about the K30A that is used to allow the wet/delay signal to pass or not. If you jumper the drain and source pins/pads, then the JFET is bypassed and the delay signal is essentially "on" permanently.

Keep in mind that the overall switching electronic circuit could be fine, but that single JFET is buggered up such that telling it to turn on does not make it turn on. Our troubleshooting strategy here is to determine if, when the JFET is factored out of the equation, you are able to hear acceptable delay signal. If no clean delay signal is heard, then the problem may lie in the delay chip itself, rather than the electronic switching, since you note yourself that a) clean signal seems fine, b) the controls seem to produce the expected changes, c) the quality of the delay signal is at issue.

The datasheet for the JFET can be found here: http://www.toshiba.com/taec/componen...c//53/6919.pdf

It appears that the two pins to jumper are pins 1 and 2. These would be the left and middle pins, if the transistor was facing you with the flat side, and the pins were pointing down. You should be able to simply temporarily solder on a small jumper wire across those two solder pads on the copper side of the board, and try out the pedal. Note that, until you desolder and remove the little jumper, the chorus will be permanently "on".