dumb newb questions about troubleshooting a digitech pds1002

[pinkjimiphoton]

hi guys, got one of these in trade the other day...
cosmetically, it's in great shape, other than being dissassembled....gotta get nuts for the pots, knobs, and screws for the back plate, but other than that it's complete.

i tried firing it up...dead on arrival.

so i tried taking some voltage measurements...i have b+ going to d1, but that's where it stops...there's a 7805 there, reading 9.84v on the input of it, but nothing on the output of the transistor. actually, getting nothing after where the b+ hits the 4001.

am i correct in assuming that the 4001 and the regulator took a hit with a bad power supply? or could a short further down the line cause it to do this?

i'm figuring if i'm gonna get it working, i've gotta start with the power supply.

if anyone needs the schematic, i can post it.

i'm thinking replacing these first two components may be the way to go...is this reasonable?

i'd be thinking it was a ground problem, but i stuck the black lead of my meter into a screw hole in the chassis, and traced the voltage from the battery to the first two components...i figure if ground wasn't connected, i'd have no voltage flow at all.

appreciate the advice...thanks guys

[Electron Tornado]

Make sure you have continuity between the legs of the regulator and other components that connect to the respective legs. If the connections are good, and you still have no voltage at the regulator output, then I'd say the regulator is bad.

If you're looking for parts for pedals, Smallbear usually has a good selection and will sell hardware in "onesies and twosies". 

[pinkjimiphoton]

hi, ET, thanks for the advice.

i have a bunch of 7805's from earlier projects...and no continuity with a test between the legs of the regulator...i have 9v going to it, after that the circuit is dead.

so i'll replace the regulator, and see what's what...do ya think i should also replace d1, a 4001? i checked it, it seemed good, but i'm wondering if it took a hit, too.

fwiw, here's the schem:



the thing i don't get is why i'm not reading 9v at q1, either...it's weird, it's  a straight shot from the power supply to the jfet there. maybe i should replace q1 too then? something's nuking the entire power supply, and the first things in line are the 5v supply and the 9v supply going to the regulator and q1 respectively.

thanks, i really appreciate the help and knowledge!!

[Electron Tornado]

You could just remove D1 and see if anything changes.

As for Q1, remove the voltage and check for continuity between that leg of Q1 and the input of the regulator (since you know you're getting 9V at the regulator input). There might be a bad trace on the circuit board or a bad solder joint at Q1.

[pinkjimiphoton]

awesome, will do as soon as i get a chance to hit the bench.

thank you!   

[petey twofinger]

i got one of those when they came out , it was 220 $ . worth every penny , i LOVED that pedal .

it got lost for YEARS  in the trunk of a lime green volvo that had the truck opener thingy broken off . i pried hat open before it went to the bone yard and almost pooped i was so happy to find my delay , and it worked .

took it to the rehersal spot , used it once . next time back it was D.O.A . i held on to it for years eventually throwing it away like a total moron . then my old guitaist admitted he plugged his sons remote control battery into it and smoked it , to take it to a jam night or something really f-ing lame . that guy was a real class act , he had money too . who does that ? what a jag goof  !!  

every time i see one of those things i go thru several stages of grief , denial , anger , longing , self loathing , contempt for mankind , and then remorse .

i really hope you can get her runnin jimi , i had a lot of fun with that unit for many years . now i want one !(  srry to ramble )

please do a SPT with her , hook up a mic for bella too .

[pinkjimiphoton]

petey,

your story done touched my heart. in your honor, i will try to get it running again!!!

so far, GOOD NEWS... i replaced the 7805, and have a SOLID 5 v b+ going.

i also replaced q1 , a j111 with an mpf102...the only jfet i had on hand.

it is now passing signal, but i can't switch the effect on (tho the repeat hold IS working, led and all)....i did some research, the jfet i used will let it fire up, but the voltages are way
the heck off... i should be getting 9v off g, but am only getting 3...probably why the effect isn't working.

probing it with my meter (damn, that sounds dirty)  i'm getting the same 3v at all the 9v b+ test points....

so i'm gonna assume the pedal survived, it looks like either an overvoltage, or wrong polarity (more likely) roasted the jfet and the regulator....i don't understand why the hell in their infinite wisdom freekin' digitech used a reverse polarity protection diode like a 4001 in a 10v circuit..the diode survived, the regulator and switch took the hit. actually, i do understand, kinda...it's a part of a half wave rectifier. but...i think it shoulda took the hit before the other components, so i think i'm gonna replace it with maybe a 10v zener or something, if that's safe to do.

since i can't get a j111 locally, gonna sub an NTE 468...it's equivalent, and in stock at my local parts guy, so tomorrow i'll take a ride and pick a couple up.

gonna replace the 102 i put in, and hopefully the circuit will come back to life. i'm hopeful the rest of the board survived, as when probing i can hear it in the output of the pedal, and the voltages are all pretty consistent with the schematic, just off by 6 volts or so.

unless someone can suggest re-doing the resistors to make the 102 close enough to the 111...lol..

wish me luck!! advice, of course, appreciated.

if i don't like this thing, petey, we'll talk, ok? i gotta put a little cash into it to ressurrect it,  nothing major, just nuts knobs and screws (man, EVERYTHING sounds dirty...i think i got poked on facebook too much today!!)

stay tuned...

[pinkjimiphoton]

replaced the jfet with the nte equivalent...got the 9v supply up some, but only to about 6 v...messed up a trace, too...arrgh...
but it's passing audio, it's gotta be something stupid.
is there someplace in the circuit i can bypass the switching on one of these things so i can see if the circuit works?

advice?

clueless here!!