Dunlop - UVI Univibe revision A 1997 [SOLVED]

[gtr-fxr]

clean signal is fine but when you engage the effect theres no signal and the chorus/vibe led dims and if i unplug it and then plug it back in i get the effect but as soon as i hit the bypass the same thing happens again

Schematic for reference.

[lolbou]

Please specify what version you have. There's a schematic available here if it matches your unit (it may help).

I would check the ribbon wires first (those going to the LEDs and Switches board) for any broken one.

[gtr-fxr]

it's a rev. A board 1997. in the process of replacing the ribbon cables now

[RnFR]

could be the switch, or part of the electronic switching if that is what it uses.

[gtr-fxr]

it's something with the switching, but i don't see it on the schem.

[DrNomis]

Could also be an issue with the led driver transistor, if it's anything like the original Univibe circuit, I seem to remember reading somewhere that the lamp driver transistor in the original Univibe was under considerable stress and tended to go faulty after a time.....

The reason why I'm thinking that, is because the led dims after some time, so there's a clue, also the lack of signal when the effect is engaged is another clue, sounds like something is diverting alot of the signal to ground....

[lolbou]

if it's anything like the original Univibe circuit

The switching is way different.

Could also be an issue with the led driver transistor

No it's not because:

then plug it back in i get the effect

. So the lamp works fine (remember that the buld is driven at all times in a Univibe, no matter if it's bypassed or not)...

Switches are Carling SPSTs and are easy to check. From what I recall, poor LED function and switching issue were mostly related to faulty wires.

If changing the ribbon wire doesn't help, check the expression pedal jack to see if all three poles are operating a good connection when unplugged.

Then if it still doesn't work, check voltages and logic levels around CMOS ICs, and let us know.

it's something with the switching, but i don't see it on the schem.

What can't you see?

[DrNomis]

Ah right Lolbou...


Mind you, it's hard to know what could be wrong without a schematic for this particular model of Univibe......

[lolbou]

Mind you, it's hard to know what could be wrong without a schematic for this particular model of Univibe......

There's a schematic available here if it matches your unit (it may help).

When I meant here, I actually meant here at FSB. And you're actually the first to reply in the thread.

[gtr-fxr]

OK, changed the ribbon cable and no change, off to check voltages i guess. and im pretty sure i already checked the expression jack but ill check again.

[lolbou]

im pretty sure i already checked the expression jack but ill check again.

Just recheck continuity between each lugs (by pair) when unplugged.

OK, changed the ribbon cable and no change

Damn... Sorry to have misquided you... I've added some glue around the wires to prevent the new wires from mechanical stress in the units I've repaired, you may want to try it too?

Regarding your issue, I would especially look over U5 and U6 logic states, though pretty all of these can be responsible for the bug. But anyway, if you're coming up to changing a logic IC, then here D_H's advice : cut the legs with a pair of pliers along the IC's body, remove the body, and pull each leg by applying heat with the soldering iron.

[DrNomis]

Mind you, it's hard to know what could be wrong without a schematic for this particular model of Univibe......

There's a schematic available here if it matches your unit (it may help).

When I meant here, I actually meant here at FSB. And you're actually the first to reply in the thread.

Ahhhh....silly me....

Oh well, at least I know now anyway.....

Cheers Lolbou....

[gtr-fxr]

something tells me its U5 for some reason. and now when i unplug and plug back in i get the effect but no led.
Oh .. and U1 seems to be getting awfully hot, dose that seem right

[lolbou]

and U1 seems to be getting awfully hot, dose that seem right

Did you check you power supply voltage? The regulator may warm up a little, but I can't remember it being "hot"... Some shorting or dead IC might explain?

something tells me its U5 for some reason

What reasons? U5 logic states are easy to guess and check (schmitt inverters)...

Let us know!

[gtr-fxr]

it was just a guess really,
i can post voltages if that will help.
how do you tell what state the inverter is in

[lolbou]

how do you tell what state the inverter is in

It's either high or low, that is A or B+ (around 15V) or ground. Once you know any input state, the output of the inverter has to be the exact opposite.

i can post voltages if that will help.

All ICs get the good DC supply? Does the regulator delivers the very 15V DC?

it was just a guess really,

That's still where we are at the moment, but we'll work it out!

[Dirk_Hendrik]

how do you tell what state the inverter is in

It's either high or low, that is A or B+ (around 15V) or ground. Once you know any input state, the output of the inverter has to be the exact opposite

Which applies to all logic components in the circuit. Look up their datasheets and see what the outputs are supposed to do depending in the inputs. The flipflops will be a little bitchier though.
However, it's cost vs time.
My Dunlop Univibe had died of a defective voltage regulator and the one first of the logic components I started measuring was an XOR gate that had 2 highs in it's inputs and a high on the output. That should never happen. At that point I decided that I could a) a couple of hours of faultfinding (lolbou had not drawn that schem at the time) or b) take out all logic components and replace am all in one go. That was an hour of work and some 4 euro's of chips. I went for option b and had a working vibe in a hour.

cut the legs with a pair of pliers along the IC's body, remove the body, and pull each leg by applying heat with the soldering iron.

Like this. Would have taken considerably longer desoldering all chips pin by pin.

[gtr-fxr]

so far i checked voltage on U6
1:17.5vdc 8:17.9
2:0 9:0
3:17.5 10:17.9
4:0 11:17.9
5:17.7 12:0
6:0 13:17.9
7:0 14:0

and U5
1:17 8:17
2:0 9:17
3:0 10:0
4:17 11:17
5:0 12:0.7
6:17 13:0
7:0 14:16

the voltages shown are "i think" bypass cant tell since the led for bypass burnt out
but when i hit the bypass switch and the chorus/vibe led dims all ov the pins with 17vdc drop to about 6vdc

[lolbou]

so far i checked voltage on U6
1:17.5vdc 8:17.9
2:0 9:0
3:17.5 10:17.9
4:0 11:17.9
5:17.7 12:0
6:0 13:17.9
7:0 14:0

Should be A+, so some 18VDC (straight power supply voltage). Considering that U5's pin 14 is at 16V, and that these are running in parallel, there is something catchy there... U6 smells bad to me.

but when i hit the bypass switch and the chorus/vibe led dims all ov the pins with 17vdc drop to about 6vdc

Definitely not good, and most probably explaining the regulator overheating (it's checked ok, isn't it?).

edit: oh wait, A+ has nothing to do with the regulator...

[gtr-fxr]

any where else i need to check? and the A+ is being fed from pin 1 of U1 which would be 18v right?