Line6 DL4 problem - No output, just squeals, but it's still functioning??

[Citizen_Insane]

I've got one that died on me just days out of warranty (6 month warranty? wtf?) Anyway, here's what happened and the symptoms.

One time when I was playing, I got a little carried away and I tripped on the power supply which ended up shorting a bit. I immediately unplugged the pedal and resoldered the PSU so that it was working correctly (verified with a multi-meter).

Anyway, now when I plug in the unit (I've since switched to a higher quality PSU) I get a high pitched squeal from the pedal that starts about 2-3 seconds after it powers up. I tried pulling the chip in back to reset it and I also tried doing a soft reset but neither did any good.

Although the pedal doesn't produce sound, I can tell the CPU is still working. the tap temp still works on those functions that have tap tempo, the looper still works, I just don't get any sound. All the LED's and stuff light up too.

Anyone have any ideas what I could do to fix it? I'm hoping I don't have to replace any of the SMD microchips, because that would be a bitch to do even with a nice soldering station.

[Enzo]

When something dies "days out of warranty," present it anyway. Most companies won't nickle and dime you over a couple days. PLus the old, "This died a week ago, but we've been on tour..."


How does it perform on the old lesser quality power supply?

DO any of the controls affect the sound at all?

[Robert M. Martinelli]

Hi,
AFAIK the Line6 DL4 has an AC power supply ( 9VAC ), plus a terribly ( and unnecessarily ) complicated inner voltage regulating system. They first reduce the voltage to 3V and then use a doubler to bring it back up to 6V.....

Before trying something else I would follow Enzo's advice and contact Line6 ASAP, chances are they'll fix the unit for free or for a nominal fee.

I agree a 6-months warranty period is not fair ( here in Europe the warranty period is at least 2 years ).

If you're using a different AC adapter, be sure its output is not greater than 9 VAC, otherwise you're likely to overload the tiny and fragile SMD voltage regulators. Most importantly, I think that if you use a different adapter, the warranty could be void.

The Zeners are likely to be damaged as well, as they're a well known issue on DL4s.

BTW Working on the DL4's power supply circuitry is a real PITA, I recently fixed one and I ended up extensively modifying the power supply circuit/layout and using a 7806, simpler and more reliable.

HTH

Best regards

Bob

[Citizen_Insane]

Well, first off, it died probably a year ago. I just got it back out of my box of random electronics gear because I read a post on the internet about fixing it.

Also, I did contact Line6, but they didn't seem to care, they just told me that they could help me find a service center where I could pay $60 an hr to have someone fix it. Uh yeah, screw that.

I also forgot to mention that it does not work on battery power, that was the first thing I tried. Also, the power supply I'm using is putting out 10.1VAC. It's the only one I've got unfortunately, the old one I broke is dead or gone now.

Ok, so on to fixing it, since that's my only option right now. I agree that I think the power circuitry is probably what's dead. I can pull the D12, D11 and D16 and check them (I think those are the zeners, not positive tho, please confirm).

I'm all game for trying to fix the SMD components as well, so if you think the voltage regulators are blown, I can replace them. I'll need a new tip for my Hakko, but that's no big deal, I wouldn't mind getting a smaller tip anyway.

Since there aren't any schematics for this thing available, how do you guys suggest I go about trying to decipher the circuitry?

edit: Just tested the zeners and here's what I found:
D12 - 9.8V
D10 - 9.8V
D16 - ~1V

Hm....that seems kinda strange. Think it's possible D16 is blown and therefor preventing voltage to continue through the circuit? However, I just read that Zeners usually fail shorted, not open, so would it would make more sense that D12 and D10 are the ones that failed? Not a whole lot of useful info about this one, but I do know D16 is a 2EZ3.6 Zener Diode.

[Robert M. Martinelli]

Hi,
You're stating the unit doesn't work even with batteries, so my first suspect is the MAX887. Lift D11's cathode ( which, BTW, is not a zener, it's an 1N4002 ) to isolate the MAX887 from its supply.
Connect the batteries, or put 6VDC/1A between pins 8 ( +in ) and 5 ( GND ), and check for 3,3 VDC between pins 7 ( out ) and 5 ( GND ). If you get 3.3VDC on pin 7, then the MAX887 is good, so your next step is to check the MAX660, here used as a voltage doubler.

You should check the 3,3 VDC input between pins 3 ( +in ) and 5 ( GND ), if they're not there the 33mH inductor is open. If you have 3,3VDC at the input you can move ahead and check the output, you should have some 6,5VDC between pins 8 ( out ) and 5 ( GND ). If so, the MAX660 is good, so you can move to check the LM3480 ( 3-pin 100 mA VR ). Check if you have 5VDC between pins 1 ( out ) and 3 ( GND ).

( It's also a good idea to check the tantalum caps around the above mentioned ICs, as they fail from time to time ).

Hope this helps

Best regards

Bob

[Citizen_Insane]

Bob, I have to say, you're awesome. I'll try that out tomorrow after work.

[Dirk_Hendrik]

Bump,
Thanks for this thread (as well as some others online) for helping for to figure out the bizarre topology of these power supplies.

Bottom line: LM3480 defective. The Max660 was dead till I isolated its output (temporarily cutting a trace) from the LM3480. The in and out of the LM3480 measured some 36 ohms in both directions. Maybe usefull to know when someone runs into the same problem.

[jimosity]

I recently fixed one and I ended up extensively modifying the power supply circuit/layout and using a 7806, simpler and more reliable.

I sure would love to know exactly how you did this and where you made what connections.

[Robert M. Martinelli]

Hi Jim,
Unfortunately that happened more than one year ago, I did what I then thought would have been a "one off" mod, I don't do this for a living, so I didn't trace down the mod schematic, as I didn't expect crowds of desperate DL-4 owners to knock at my door....

Best regards

Bob

[Threlyn]

Hi, I know this is an old thread, but I've been having the same problem with a dead dl4 that does not work with either batteries or the adapter input. I lifted the D11 cathode and put in batteries. I measured 3.33VDC between pin 5 and 7 on the MAX887, so I think that one is ok. Moving on to the MAX660 I measured 3.3VDC between pins 3 and 5, and 6.5VDC between pins 5 and 8. For the LM3480, I measure about 5VDC between pins 1 and 3. It seems the usual suspects check out, but I still don't have a working pedal. What would be the next step to try and track down the problem? Thanks for the help.

[Robert M. Martinelli]

Hi Threlyn, and a hert felt-welcome to the forum!

What do you mean by saying that the unit is not working? Do the LEDs light up? Does the "dry" signal make it through the FX with the FX bypassed/off? If the voltages look OK and the LEDs work but the sound doesn't make it through the FX you could have a problem along the signal path ( bypass circuitry, jack sockets ). Help us to help you by giving us all the details you can and being more specific...simply saying that "the unit doesn't work" is not an accurate enough description of the fault your DL4 is suffering. Also, allow me a word about "good netiquette"...Starting a new thread rather than hijacking an existing one helps a lot in keeping all the available info on this forum well organized and therefore easier to find/consult for everyone.

Hope this helps

Best regards

Bob