MXR Flanger problem

[Alexi]

I'm completely stumped - it's am original gray box model. When effect is engaged, no effect is head, just a slight dip in volume. Right when you turn it on, the effect works for a few seconds then switches off. Then you hear 120 hz hum slowly fading away. I replaced the power supply caps. The regulator is at 14.6vdc. I Swapped SAD1024s - no change.

[oldschoolanalog]

Problem might be one of those tantalum caps in the LFO.
Hold a 1uF or larger Non Polarized cap across the outside legs of the tants. If it/that works, you'll need to replace the LFO caps.
A while back that idea was posted and it helped me diagnose & repair an old 117. I forget who posted it but, Thanks!
Take V's yet? Audio probe it?

[Alexi]

Placing an NP cap does nothing. Audio probe shows no signal coming out of SAD1024. Maybe the new one was dead also. Voltages are normal, as far as I know.

[Govmnt_Lacky]

Audio probe shows no signal coming out of SAD1024.

Ahhh yes! But, does it show a signal going INTO the chip? 

[Alexi]

Pin 2 Ch A yes, Pin 15 Ch B you could hear it veeeeeeeeeery faintly if I jack the test tone all the way up. Could be just bleedthrough?

[oldschoolanalog]

Here's the schematic. Print one and start signal tracing from the input.
http://www.diyguitarist.com/Schematics/MXR-Flanger-Schem.jpg
First make sure all your V+, Vbias & Grounds are correct and where they belong.

[Alexi]

I was away for a while - now I'll be back to repairing it. Well, the good news is that both Reticosn were tested in a an Electric Mistress and they work! Signal goes into pin 2, nothing comes out of 11/12. I'll check the rest soon.

[Fender3D]

At SAD's pin2 you should have the bias DC.
Check it doesn't change from switching the unit on.
If it does it may be C1 leaking, or U2.

You won't have signal from BBD without clock either.
Check the clock signal at U3's pins 1 AND 2.
Again check for any change from switching the unit on (as you said in post1, the unit works then quits...)

[jdub]

Alexi, did you ever have any success with this problem?

[Alexi]

I've been very busy - I just decided to shotgun the board. I will rebuild it soon, with IC sockets. At least I have two Reticons now!