dunlop univibe woes

[pinkjimiphoton]

so i picked up a broken dunlop univibe, rev b 1995 according to the boards.
its got the stacked board setup, with the ldrs and lamp on a smaller board that connects via sip headers and sockets. its a BITCH to follow the damn thing, cuz it jumps between the boards, and the board need to be connected for it to power up.
it doesn't have ALL the bs cmos switching, but does have a fair amount of it.

i replaced the voltage regulator and associated caps. i have good voltages just about everywhere. all the knobs work, the lamp <an led temporarily> is flashing, and you can hear it switch between modes if ya crank the amp up. it is NOT really bypassing tho.
i tried cleaning the treadle jack, no diff. replaced it as i had seen that suggested on all the threads i looked at.
touched up solder joints on the board. checked for continuity. everything seems good

but

its barely, just barely passing audio thru it. the schematics for the actual univibe and the dunlop ones that lolbou and dirk posted on FSB aren't even CLOSE to whats in this one. so i need to kinda figure out where the signal is getting lost.

i DO have a generator, and have pumped signal in the front of it and used my audio probe thru the circuit.. but without the schematic, and being split between two boards, i just can't follow the damn circuit from the output jack back.

most nodes on the circuit board will produce either the dry or modulated tone it seems like, at various levels.

on the top daughterboard, there's a quad opamp, a tl074. to me, it seems suspect as the voltages on the right side of the chip aren't what i'd expected to see there...  (labeled u1 on this particular variant)
pin 14 is close to 14v, pin 13 close to 15, pin 12 around 10, then it seems weird and off.. i forget the exact voltages, but if memory serves 11 was around 7 volts, 10 around 0, 9 the same etc.. just doesn't seem like the other voltages, or what i'd expect which makes me suspect that quad. gonna suck the solder out and replace it and try again, but...

i'm freekin lost. anybody else ever deal with this particular issue? maybe buy me a clue?
thanks peeps

i may make a decent fuzzbox, but this actual electronics shit is above my paygrade i think

i DID contact dunlop about a schematic, as yet, no reply...

to be continued <hopefully>

at least its actual thru-hole components on this one.

[pinkjimiphoton]

 
i dunno why i always second guess myself so much.

yep, it was the tl074. i didn't have any, so i socketed it and tried a tl064 and84, the 84 just barely seemed to sound better.

so i replaced that quad opamp, hiss gone, volume good vibes and choruses. all good.

also had to replace the 14584 hex schmit trigger. i didn't have one. a 4069 worked perfect. switching now works correctly. an inverting hex inverter is an inverting hex inverter... in this circumstance, anyway.

for the power supply issue, only the 7815 regulator and the two 470uF @35 caps needed replacing.

i may go back in and undo the couple changes i had made,  i had replaced a 3904 that was wired as a diode (b/c connected) that i thought may have been a mod with the two 914's that i assumed were supposed to be there. also added one other diode where it was marked on the board but not installed.

with the led in it it sounds more like an earthquaker devices "the depths" than a univibe. cool sound, but tomorrow means a trip to the local jobbers just for a 12v 40-80ma leaded grain of wheat lamp. the led doesn't fade the same.... tho they DO throb a bit more. i'll install that and call it a day.

one other thing i found was if the chorus/vibe led is dead like mine was,  you can steal the bypass led... same one is used in both places, its a dual led, green forward biased and red(dish) reverse biased.  so just swap it over and replace the bypass diode with any colour you like. i chose pink for obvious reasons... mainly i have a shit-tonne of them.

anyways, hope this helps someone down the road with one of these things just sitting there doing nothing but looking at ya funny.

anywho...

onwards n upwards

[Slowpoke101]

You got it working again! Good work 

I'm still looking for a suitable schematic but, as you found, its almost impossible to find.

Cheers.

[pinkjimiphoton]

thanks ian!
and thanks for the help, too!!

[Finom1]

I could not find a schematic.

[pinkjimiphoton]

there isn't one, apparently. dunlop is blowing me off about it, and this particular incarnation is unlike any other i have seen... not that i haven't seen this version a couple times, but usually its either more based on an actual univibe or like the rev a schem that lolbou and dirk came up with.

other than a couple semis, the one i have is different from all the others pretty much. it has weird switching, but much more standard parts.

i wish i could see it well enough to trace the dang thing, but the glaucoma makes it real hard to focus on stuff like this one.. its gotta fiberglass or epoxy board, but you can't follow the traces on it on the underside, it is covered with like, a pattern or something with a mess of solder pads on it.

way above my humble fuzzmonger paygrade!

that said tho, voltage tests were what saved my ass. check all the voltages, and where ever its wrong, suspect the passives associated. if they're ok, try replacing the semiconductor thats reading weird and odds are you'll nail it.

just don't scratch yer nards too long second guessing yourself

rock on peeps.... LLAP