Line6 DL4 power supply repair

[beatnik]

i've fixed a dead DL-4 i got off ebay. probably wrong power supply had been used, so I replaced some of the diodes and regulators in the power supply circuit

now if i power with batteries, all the voltages are fine and delay works as it should

i still have some problem using an external 9V AC power supply (2000mA)

at 6V DC point I have about 14VDC instead !! I haven't tried if the delay works because rating for the MAX887 is maximum 11V so I unplugged it quickly to avoid burning something again.

if i lift D11 cathode off the pcb and measure the voltage i got about 5.5V DC which should be fine

if the diode is put back on the circuit the voltage on that point rises up to 14V DC which i really suspect it's not ok

i am wondering what is the problem here.

any help is highly appreciated

power supply section schematic

DL4 ps

[g1]

Did you replace D16 with correct part & polarity?
Are you using the line6 px2 supply? If not, it may be putting out more than the 9V you want. What is the AC voltage measuring at the jack?

The lower DC voltage when D11 cathode is lifted is because you have disconnected C40 from the circuit and you are measuring a half-wave rectified pulse.

[beatnik]

the power supply is not an original Line6 but my Whammy power supply. It's rated 9V AC but actually I've just measured and outputs 10.7 V AC instead

i've used a 3.3V zener instead of 3.6V and 1N4007 instead of 1N4002

do you think the problem is the power supply or the diodes ?

[dwmorrin]

I've powered many a DL4 with the whammy supply, so I don't think that's a problem.
I always run DL4s under test with my bench supply using 9 or so volts dc and a "tip positive" 2.5mm plug.
The MAX 887 datasheet gives 12V as the max between +V and GND.
I'll go out on a limb and say maybe you're being too cautious... maybe you'll be ok if you let it power up.
If you want a "safer" option, try using a 1spot with the L6 adapter (converts 2.1mm neg tip (BOSS) to 2.5mm pos tip (Line6).

[beatnik]

i've checked again using the whammy power supply and the voltage at the 6V point is up to 15V instead ! definitely not ok for the MAX887 regulator

i've even tried to replicate the circuit on breadboard and i get the same result.

so i guess the power supply must not exceed 9V AC

however, if i put two 3.3V zener diodes in series i get more voltage drop and the result is something around 11V which should be better

do you think it would be safe using a 6.6V zener diode and keep using the power supply i already have ?

[dwmorrin]

The zener will cut more voltage off the top the higher the value is.
6.6V would get you into trouble when using a 9Vdc adapter.
Ditch the non-original adapter before modding the pedal to accept it.
Get the original L6 supply, or the 1spot adapter. Either one should be ok. The 1spot will only give you 9V, so you won't have to worry about the expensive chip with that option. Make sure you get the "L6" converter tip along with the actual supply.
And order a replacement zener that is correct original value just to be sure.

[beatnik]

i have discovered my bbe supa charger power supply has two outputs at 9V DC 250mA. i also got the adapter from an older power supply.

with this option the pedal runs smoothly and i got 7V DC at the test point which is perfect

thank you very much

[dwmorrin]

Good! Glad its working for you.
I just opened up a fixed DL4 that's just waiting to be picked up... and I probed around to see if I could get your same high voltage reading.
I used the whammy adapter and didn't see anything funny...
Then I unplugged the input jack, but left the ac power connected. I DID see near +13V when I probed the + battery terminal (I am just probing the rear of the board/don't want to disassemble this again right now).
Plugging the input jack back in (and thus turning it ON), the voltages drop back to normal.
Is this possibly what you were doing? Probing without the device turned on?

[beatnik]

you are right !

i thought that the jack switching only worked for batteries !

if i insert the jacks i got about +9V on the battery terminal. is it too much ? i mean, MAX887 can take it for sure, but what about the rest of the circuit ?

anyways, i think i'll just stick using the 9V DC supply with adapter cable which is more handy

[dwmorrin]

With my whammy connector, I was probing what I believe are the various big electro through hole caps at each supply voltage node... I was getting +6, +3, +5, -5... and yes I think I remember reading 9V at the battery +.

That schematic snippet of the DL4 implies there is a raw +6Vdc rail there, but I think that might be false. That probably just refers to the 4x 1.5V batteries. I think the only rails the sensitive elements of the pedal sees are after the MAX887, especially since there is a 6.6V rail created in the next stage (MAX660).
I think its fairly safe to assume that anything else connected to the "+6Vdc" point will do fine with +9V.

[beatnik]

nice

thank you very much for helping

cheers