dod delay fx90 question

[icepot]

hi.

i bought a DOD analog delay second hand about a year ago, and up until last night i had absolutely no problems with it. last night i was jamming with my brother and i went to turn it on and nothing happened. the led came on, but no delay... nothing happened. i disconnected it from the chain of pedals and started fooling around with it ... twisting all the knobs eventually gave me a small reverb. I let it set and continued to jam. an hour later i come into the house to test it out again and nothing happens. i twist all the knobs really fast and blow down the battery casing (there is no battery cover, so i thought maybe dust or something was messing it up?). i turn it on and it and it all works, but about only half as good as it should. and when i turned the mix pot, the mix would act all right until about position 9 (out of 11) and then it would start lower in volume from there out!?!

so i woke up today determined to fix this thing. i read all the post on this and get ready to post my own questions. i go over to turn on the pedal, and to my surprise everything is working just fine! the only thing i notice is that when everything gets turned up, and then i move the delay the oscillation sounds a bit choppy or distorted when i bring it back up.

does anyone have an idea why something like this would happen? and/or a way i could make it more reliable? i would hate to be on stage, and then have this thing shitout on me!!! its one of those pedals that your just in love with it and for me seeing it in this state is like watching your dog slowly die.

thank you for taking the time to read this,
mychael

[Mark Hammer]

Whenever time makes a difference in whether something works properly or not, the usual suspects that the FX police round up for questioning are the caps, especially the electrolytic ones.  That's not to say that they have a short life span and need constant rejuvenation.  Rather, their chief job is to store current over time, so when something goes wrong with one of them, it tends to show up in pehnomena that changes over time.

[icepot]

mark, thank you for the reply...
i don't know how to look and see if a cap is bad, however i would definatly be willing to learn. i have a mutimeter, i just don't know to much about it. i'll look around the web and see if i can figure it out.

i also forgot to mention that the other day i made a dumb mistake of hooking my instrument into the out, and then hookng the in of the pedal into an mixer. the next time i tried to use it, it started messing up! this wouldn't have anything to do with it not working right would it? also could it be a bad pot?

EDIT::
by the way, here is a link to the schematic
http://i83.photobucket.com/albums/j287/fallingfurtherchicago/dodfx90schematic.jpg

[jonathan perez]

plug that sucker in and check for voltages on the electros. you should be getting around 9 volts. if you arent, theres your problem.

[Dan N]

An old radio repair trick was to turn the malfunctioning radio on and bridge the caps with a good cap. When the radio shot back to life, you knew you found the bad cap.

Heh, just throwing that out there.

[Mark Hammer]

Off the top of my head, I'm going to say there are 4 caps to "bring in for questioning".  One is the 47uf cap on the power supply line (upper left hand corner of the schematic).  The second is the 47uf cap feeding the power for the clock chip and BBD (that's the one adjacent to the diode in the upper right hand quadrant).  The 3rd and 4th are both 10uf units.  One smooths out the Vref coming from the pair of 22k resistors in the upper left, and the other is part of the compander, between the pair of 22k resistors on pin 12 of the NE570 chip.  All of these could be expected to screw with the sound in a big way if they were erratic and shorted out.

I think the suggestion of bridging each on the copper side of the board with another cap is a great idea.  You can probably use a new 10uf cap to try out each of these possible culprits without any harm coming to the effect.

[icepot]

thank everyone for the help. i really appreciate it!

allright, i will try the 10uf cap next time it goes out. hopefully it wont go out though.

when i was looking at the board, the copper side where the traces should be is very faded away. theres spots of clean copper, but for the most part its very faded, almost as faded as the board itself. is this normal aging? when i flip it though, you can see the traces good, its like there in the middle of layers of the board.

but, thank you guys again.
you have given me hope that all is not lost with this pedal!
thanks,
mychael

[george]

An old radio repair trick was to turn the malfunctioning radio on and bridge the caps with a good cap. When the radio shot back to life, you knew you found the bad cap.

Heh, just throwing that out there.

That sounds like a great trick to me!

Thanks!