Boss cs-1, VTL5C3 optocoupler help

[mckenzie]

Hi, am new here so hello

I have a dead cs-1 (well not completely, there's just no compression, just a clean signal) & want to check the optocouplers out of circuit. Is there a basic test i can do? I'd assume looking at the data sheet with them in the off state (no connection to the LED) that i'd get around 10M ohms across the LDR ? Never used these before so any advice would be good, i see they are very expensive too!

thanks

[armdnrdy]

Here are a few items that you might need.





You'll find that I marked the location of the optocouplers on the schematic.
I also marked the polarity of the LED side as well.

First thing you should do is test the optos in circuit.
You'll need to put some sort of a signal into the input of the effect. You strumming a guitar will do.

Using the resistance function of your meter, check the resistance between the two photo resistor leads. Take the first reading with no input signal, and another with a signal. Repeat for the other photo resistor.

With no signal you should be reading in the MΩ or out of range of your meter, and with an input signal Ω to low KΩ.

The LEDs are connected in series.....which means if one goes bad...neither work.
Using the DC function of your meter, connect the black lead to the - and the red lead to the + of the optocoupler LED.
Now test the next optocoupler.
Repeat with input signal.

Write down all readings and post results.

[duck_arse]

set the sustain pot to max resistance, and what armd said.

[armdnrdy]

set the sustain pot to max resistance, and what armd said.

Good call!

[mckenzie]

cheers for looking at this, lll take a look & post the results

[PRR]

Does the DC voltage at the collectors of Q4 Q5 go down when you beat it?

[mckenzie]

Measurements from PH1 + 2 were identical

no signal
cell - 19.5k ohms
LED - 1.3v

signal
cell - 0 ohms
LED - bounces from about 1.45 - 1.5v

Q4 & 5 collectors
no signal 6.3v
with signal bounces around from about 0.5v to 3.9v

Resistance of both the cell's read open circuit when its out of circuit, this can't be right. Also worth noting is the treble switch does nothing to the sound.

thanks for the help guys

[mckenzie]

so it looks like the LED drive, op amp & switching circuits are good & both these optos are bad ?

anyone know a good place to get VTL5C3's any cheaper than £15 each on ebay ?

cheers

[Kipper4]

try dr tweeks for uk

[mckenzie]

f**king brilliant kipper, i didn't know about this guy, he has them in stock as well!

cheers for all the help

[mckenzie]

Hello again.. following up on this I put two new VTL5C3's in & it worked for a bit... now it's back to how it was before - no compression!

I've taken the new optos out of circuit only to find they are both now fried as well - ie the LDR resistance now shows open circuit - same as the old knackered VTL5C3's I took out to replace.

I did check the resistance of the new ones before i put them in and they read around 30m ohms each as far as i remember, so there is nothing wrong with my meter.

Any ideas as to whats causing them to go bad would be great? I've checked the .47 cap that goes to ground from PH2, seems ok.

Should i suspect the op-amp or perhaps Q1 ?

thanks for any help

[armdnrdy]

Check the resistors on either side of the Vactrol LEDs. (4.7K & 330K)

Also, check both zeners. The main power zener (RD11EB) and the Vactrol LED zener. (RD5.1EB)

[duck_arse]

I was going to suggest sticking a fixed R temporary for "PH2" (10k? 1M? 1k?) and a pair of bare red leds for the vactrol leds, then you could give a thrash and monitor the leds, see if it is the vactrols or something more sinister.

[mckenzie]

Thanks guys, I appreciate the suggestions. Ill take a look at the weekend & hopefully shed some light. 

[mckenzie]

On closer inspection it looks like i have a different board here to the one you've posted, silly me I should have looked at this much more closely.

This board is cs-1 052-288D & it's very simliar but not the 288B version posted. Several components are either added, not there or different values as far as i can see. For instance RD5-1EB is not there. Looks like the optos i need are not vactrol either, they are marked P873 on the board although a google search suggests that maybe VTL5C2's are equivalent, not sure though?

Hmm will have to look for the correct schem somewhere.

Bugga!!

Any ideas where i might source some P873's or equivalent ?

[armdnrdy]

Is there any other designations on the optocouplers? The P873 is a series (long obsolete) manufactured by Hamamatsu.

http://www.datasheetarchive.com/dlmain/Datasheets-13/DSA-241319.pdf

[armdnrdy]

Update:

I can barely make out this number that coincides with a Hamamatsu number. P873-G35-380

Info from here:
http://www.gearslutz.com/board/attachments/geekslutz-forum/324273d1357587184-loooking-service-manual-boss-cs-1-boss-cs1-compressor-sustainer.jpg

You're going to have to look at the previously posted data sheet to find the closest replacement that is still available.

[mckenzie]

Thanks a lot for the info, ill dig around & see if anything is available.

Am just thinking though that the cell in the vactrol's & P873 are not that dissimilar right? If so am still wondering whats causing the vactrols to fry - the cell that is not the LED, would need to get to the bottom of that first. Finding that out will prob involve using the correct schematic which isn't around anywhere although Ill have another look & see if that part of the circuit, the stage with ph1 & 2 in, is the same as the schematic posted here. Maybe I am talking rubbish though & should just give in, would be a shame as I love this pedal

thanks again for the help