Maestro Stage Phaser

[VintageGear]

As announced in my other thread, another Maestro in need! They all seem to die on me this year! Lets make it a success rate of 3/3, alright?! Learned a lot from the other maestro phaser, but the problem here is different. LFO seems operational based on wobbling voltages.

Problem:
Sound coming through, but no phasing effect is audible.

LED flashes and lights go on with PSU (using 9V, should be 12V, don't have one)
No lights / LED on battery (is normal according to service manual)

Repairs done:
- All capacitors replaced
- Dodgy solderjoints sucked and resoldered

Service manual with circuit:
http://www.synfo.nl/servicemanuals/Maestro/MAESTRO-STAGE-PHASER_SERVICE_MANUAL.pdf

Voltages measured with 9V battery:

ID	IC #	Pin 1	Pin 2	Pin 3	Pin 4	Pin 5	Pin 6	Pin 7	Pin 8
TL022CP	IC 1	4.0	4.0	2.0	0.0	3.8	4.0	4.0	8.1
CA3094E	IC 2	0.0	4.0	4.0	0.0	0.6	2.0	8.1	8.1
CA3094E	IC 3	4.6 - 6.6	1.5 - 2.0	4.0	0.0	0.6	~5.7	8.1	8.1
CA3094E	IC 4	1.5 - 2.0	4.0	4.0	0.0	0.6	2.2	8.1	8.1
CA3094E	IC 5	4.5 - 6.5	4.0	4.0	0.0	0.6	~5.7	8.1	8.1
CA3094E	IC 6	0.5 - 3.5	4.0	4.0	0.0	0.6	2.1	8.1	8.1
CA3094E	IC 7	4.0 - 6.0	3.8	2.7 - 4.8	0.0	0.6	3.2 - 5.0	8.1	8.1
TL022CP	IC 8	4.0	4.0	3.8	0.0	2.7 - 5.2	3.0 - 5.0	0.5 - 7.5	8.1
CA3080E	IC 9	0.0	4.0	4.0	0.0	0.6	3.3	8.0	0.0
TL022CP	IC 10	5.5 - 6.0	4.0	3.3	0.0	4.3	4.5	5.0	8.0
CA3080E	IC 11	0.0	4.0	4.0	0.0	0.0	4.5	8.0	0.0

* cant read my own handwriting lol

There should be 9v at the VCC but it's pulled to 8.0v. Also, the readings vary from 8.0v to 8.1v in a waveform-matter. That's suspicious to me?
Who is willing to shed their light on this beauty? Much appreciated once again!

[PRR]

No, the "+9V" is dioded and dropped to around 8V. I don't think that's important.

There are six '3094s in identical circuits, but giving different voltages. Oddly, pin 3 which should be hard-tied to "4V" isn't 4V on several chips.

[VintageGear]

You sure RRR? There is 4V on those hard wired ones. The ones that differ have resistors in circuit.
I tried a different approach: Audioprobe. I can find the signal at IC1B pin 7, and also on IC2 pin 1. After that it should come out of pin 6, right?? Nothing there. That should feed pin 1 of IC 3, right?
IC2 reads 2V on pin 6, so does IC 4 and IC 6. IC 3 and IC 4 read between 5.2 and 5.7 V
I dont understand these values.  Shouldn't it all be the same voltages? I mean, its the same stage over and over again right?

[VintageGear]

Anyone, am I on the right track with the audio probe approach? Thx

[Kipper4]

I don't know too much about OTAs

heres the data for the CA3094e

http://www.experimentalistsanonymous.com/diy/Datasheets/CA3094.pdf


otherwise I'd help.
If i get time later I'll take a look but dont expect too much.
Have you googled or searched the forum to see if you can get someone elses voltages?
or google a similar ota based phaser and do a comparaison.

[Fender3D]

I know google is a fast tool indeed, but...
did you read CIRCUIT DESCRIPTION and TEST, ADJUSTMENT AND TROUBLESHOOTING on manual?
There are several clues about phaser not phasing...

[VintageGear]

Thanks for the suggestions. Yeah I read through the manual and googled a bit, thats where I got the idea of audioprobing pin 6. With a signalgenerator (1khz..beeeeep....) on the input I can follow it through IC1 (buffer/signal split) and it reaches pin 2 on the first OTA (IC2), but nothing on the other side. For testing purposes, can I unsolder IC2 and temporarily jumper "pin 2" to "pin 6" (well where these pins used to be) to continue the chain? Would that work?

[VintageGear]

Found some 3094 OTA's for cheap. Bought three, I will replace the first OTA and see what happends!

[VintageGear]

Hurray! Replacing IC1 with a new OTA made it wooshhh again 
Leasson learned: Audioprobing is feasible!

[snap]

Found some 3094 OTA's for cheap. Bought three, I will replace the first OTA and see what happends!

May I ask where you found those? Thanks.

[VintageGear]

Ebay. Was worth the gamble for 1.50 in my opinion.
http://www.ebay.com/itm/1PCS-IC-INTERSIL-HARRIS-DIP-8-CA3094E-CA3094-/272041777299