Behringer Ultra Chorus UC200 Rehouse Issue

[HunkFunkPedals]

Everything works great!

Except...the LED won't light up.

I cant see why, I've tried different leds, and verified they worked before and after install but I cant get the led to work in circuit.

Here is the schematic.

that's the schematic. I really cant figure out why it wouldn't light up.

Are the inputs and outputs reliant on ground to make sure the led lights up? I'm just using the main I/O not the stereo, there is nothing on those solder pads.

I'm getting 9.25v at the anode. switching the pedal on/off doesn't change that voltage. t10 collector has 18v and across the LED pads its just all over the place. it jumps around no matter if the pedal is on or off.

[PRR]

Do you mean LD1 "CHECK"? Does the pedal go active and bypassed as expected? Then it is difficult to see how T10 can be doing a wrong thing. You do know LEDs are polarity sensitive (try both ways)?

Is the battery fresh??? (Is the wart full 9 Volts?) LD1 is designed to go dim/dark as the power weakens.

Short D9. Does it now work but VERY brite? D9 is supposed to make the LED drop-out about 7 Volts; with it bypassed it says light to below 3V.

Do you have a voltmeter? What does the collector of T10 do?

[HunkFunkPedals]

I'll try the short D9 when I get to my bench later.

I do have a voltmeter. if I'm reading the schematic right, T10 is where the power goes before D9 and the LED. So if it is getting correct voltage I'm assuming that its between ground and D9/LED.

I have pass through and effect. so everything seems to be working fine otherwise.

[antonis]

Check for "open" (blown out or burned) D9 Zener diode..

[antonis]

if I'm reading the schematic right, T10 is where the power goes before D9 and the LED. So if it is getting correct voltage I'm assuming that its between ground and D9/LED.

For T10 fully on:
V+ - V_LED - (I_LED x 2k2) - 5.6V - V_CEsat = 0

[ElectricDruid]

Once you've worked through everything everyone else has given you, and assuming that didn't work!
...then maybe try this...

If the bypass switching works, that implies that the R57B and T10 connections must be ok (if they weren't the flip-flop would be dead) but a bad connection on D9, R1, or the LED itself are all possible causes.

[HunkFunkPedals]

How would I test D9 beyond voltage or visual tests? I cant really get a solid reading on it.

[PRR]

t10 collector has 18v

How?? There's only 9V in the pedal. Maybe your meter is sick or mis-set?

Jumper T10. Measure DC Volts each point shown to ground and give us those numbers.

[antonis]

En passant:

Can't see the reason for half-supply voltage (B) taken from unregulated point (V+) instead of regulated one (Vcc)..

[Mark Hammer]

This may be a silly question to ask, but did your "rehousing" involve installing it into an aluminum enclosure with a true bypass stompswitch?

[HunkFunkPedals]

No true bypass.

Yes to new enclosure.

[HunkFunkPedals]

t10 collector has 18v

How?? There's only 9V in the pedal. Maybe your meter is sick or mis-set?

Jumper T10. Measure DC Volts each point shown to ground and give us those numbers.

1. 6.8v
2. 9.2v
3 6.8v
4. .62v
*bonus*
5. the collector is 18mv, not v

[PRR]

> 1. 6.8v
> 2. 9.2v
> 3 6.8v
> 4 0.62v
> 5. the collector is 18mv, not v



Makes no sense to me. Maybe someone else can help.

[Rob Strand]

Makes no sense to me. Maybe someone else can help.

The 9.2V and 6.8V, (1) and (2), are swapped.  Just the same 9.2-6.8 = 2.4V looks a bit high for the LED.

Putting the uncertainty in the voltages at (4) aside:  The fact (2) and (3) are the same makes be think there is a break between the collector of T10 and the 2k2 (zener side).

Use DMM continuity:
- between T10 collector and anode of Zener
- then between cathode of Zener and 2k2 (on zener side)

Surely that has to show a problem.

I suspect readings (2) and (3) are result of the DMM current through the LED and 2k2.   However
the high LED voltage still an issue.

What color LED was there before and what color LED is there now?  For these circuits to work you really need to keep the LED color the same.   You might be able to squeeze a red vs orange substitution but don't push your luck.

[HunkFunkPedals]

No continuity between R1 and D(, I guess I gotta swap that out. and see where that leaves me.

Any idea what would cause this?

[antonis]

No continuity between R1 and D(, I guess I gotta swap that out. and see where that leaves me.
Any idea what would cause this?

A picture of solder side around that area should be enlightening..

[HunkFunkPedals]

ok, retraced everything.

I had a break in a trace.

THE LED WORKS!

Now...its real dim, lol

is the 2k2 @ R1 the regulator for that?

[antonis]

is the 2k2 @ R1 the regulator for that?

It's there to limit the current through the LED..
(and through 5V6 Zener diode..)

Quiz:
For a given LED forward voltage drop (say 1.8V) and T10 V_CEsat almost zero volts, could you calculate LED working current..??

[HunkFunkPedals]

is the 2k2 @ R1 the regulator for that?

It's there to limit the current through the LED..
(and through 5V6 Zener diode..)

Quiz:
For a given LED forward voltage drop (say 1.8V) and T10 V_CEsat almost zero volts, could you calculate LED working current..??

[Rob Strand]

Think about it. It worked before with 2k2.

You either have the wrong color LED in there or you may have overheated the LED and damaged it, (or maybe the original LED isn't in there now and you have a old dull LED).