Broken Small Stone - no effect, just clean boosted sound

[yeeshkul]

I got a broken Small Stone. When engaged, it doesn't do any phasing effect at all, however the sound goes through with a little bit of volume boost. Any idea where shall i start looking for a bug (what part of the circuit)?

[theehman]

I would probe around the oscillator to see if it's functioning.

[yeeshkul]

Yeah, i see, thank you. I've also got one working unit here, so it should be aesy now. Just hope it is one of those trannies.

[Govmnt_Lacky]

Just hope it is one of those trannies.

First rule of Fight Club...

You don't talk about Fight Club! 

First rule of Debugging...

The problem is NEVER where you think it is!! 

[yeeshkul]

Thats right . There is almost no voltage at the OTA's output (pin 5,6) ... and the rest of the voltages are indeed it is steady. What IC works well instead the original? I see CA3080 doesn't have the Darlington .
The 33uF cap can be bad as well i guess ....

EDIT: i see they have CA3094E at SmallBear's

[Govmnt_Lacky]

Thats right . There is almost no voltage at the OTA's output (pin 5,6) ... and the rest of the voltages are indeed it is steady. What IC works well instead the original? I see CA3080 doesn't have the Darlington .
The 33uF cap can be bad as well i guess ....

EDIT: i see they have CA3094E at SmallBear's

Are you getting NOTHING from ALL of the ota's? That would be odd that all 5 of them went belly up.

Looks like you will need the 3094 to restore to original operation 

[yeeshkul]

Not really, the problem is in the oscillator so i was measuring just that one. Comparing to my working unit, this broken unit gives very low voltages at pin 5 and 6, which can be caused by the IC itself and maybe the 33uF cap. I've got no other idea. Both transistors in the Darlington seem to have reasonable voltages.

EDIT: i measured the other OTAs and the're all dead. This boy had it.

[petemoore]

  dahh...start lotech, look for the broken off wire end [gentle tug on wire that hides it's end, no more].
1  Taste battery or start with fresh one.
 Then a good focus session to ingest, then another to apply the suggested necessarious info the debugging sticky page details.
 Once the debugging sticky is applied, the stuff that makes it work or not work just can't hide as easy, it turns into a process of elimination, sometimes guided by intillect/analyzed experience[s...ie go for the stop-point of signal with the probe, then see what Every Gnd., V+, 1/2V?bias supply and basically what the power supply is doing...be guided by ohms law.
 It is working according to the same plan which we all abide [no choice] makes it work or not, unfortunatly now, the conditions almost make: phaser. It's always 1 of 2 ..or more things.
 After a good debug-digg-in', we'll know enough more that it'll be working or almost very-extra-ordinarily interesting soon.
  After a while it's like a test of ability to enjoy the coffee while just wanting it to be a go. 20 lessons or so sometimes before capitulation.

[yeeshkul]

Peter i am afraid i used a fresh battery. No broken wires, i measured the voltage first on the DC entrance pcb terminal. All the OTA's get a little voltage on some legs and no voltage at all on the other legs - comparing to my working unit. I'd say it was reversed polarity, it doesn't have any protection.

[yeeshkul]

Peter encouraged me to put my nose in it again. Thanks Peter. And here is what i found out:

1. The reference voltage is too low  - just 2V instead of expected 4V
2. Vcc is fine - 9V on all pins 7
3. LFO is not pulsing
4. There is very little voltage at the other OTA pins (the ground pin gives 0V)

I guess i will have to take the OTAs out of the board, gradually checking the reference voltage after each OTA has been removed.
One of them can be burned and drags the reference down.

Is there any other way how to find which one is burned?

EDIT: As Thomeeque said - the LFO is independant on the reference voltage, maybe i can put a socket there and check out which of the OTAs will make the LFO pulse ..

[yeeshkul]

All the OTAs have been removed now.
I simulated the reference voltage divider in LTspice (it is rather a tricky resistor grid, not just 2 resistors) and the reference voltage 2V seems to be all right.
However, when i measure the reference voltage right on my working unit, it starts at 2V, but withing seconds gets up to 3.5V and stays there. Any idea?