Trying to fix a DL4, aaaalmost there...

[robmay]

Hey everyone, been browsing for a while and getting a ton of help from this forum. Finally ran into a problem big enough for its own post...

I'm trying to fix a Line 6 DL4 for a friend, who bought it in non-working condition, and it appears to have never been modded at all. When I first got hold of it it was not responding at all--no lights, no audio passing, nothing. After some serious contact cleaner treatment and some resoldering of all the jacks, I managed to get it to power on and light up properly, but it was just outputting a digital screeching. After some more contact cleaner fun, reseating the EPROM, and double checking some power connections, it not only powered on but passed audio in bypass mode! Unfortunately, it was dead silent when any setting was engaged. I do know that the lights and switches respond as they should for each setting (presets, tap, and loop stuff all appear to light up correctly), and I can save presets that get properly recalled after powering the unit down and back up, and I can hear the relays switching, but that's as far as I can get it.

My friend also ordered a replacement EPROM, the guy he bought it from seemed to think that was the issue. Swapping the old (presumably non-working) EPROM for the brand new EPROM (presumably fully programmed and working, ordered from here http://www.fullcompass.com/prod/247107-Line-6-45-00-0404) only results in the whole thing not responding. Just like when I got it, no audio passes at all, no lights, no relay sounds, no response.

So basically:
-With old EPROM, DL4 powers on, passes audio in bypass mode, lights up and responds properly to switches, and saves and recalls presets.
-With new EPROM, DL4 is totally dead and passes no audio and does not light up at all.

Is the issue either EPROM? I'm getting pretty good at following circuits in analog pedals, but this is my first step into digital, so I'm not sure where to start probing for voltages and signal. My assumption is that the power section is working because the pedal properly switches and lights up (with the old EPROM). Could it be the relays? How do I check something like that? Also, any tips on removing the knobs? They're pretty stiff, and I don't want to break anything.

Thanks in advance!

[iampoor]

Have you checked all the supply voltages?

[robmay]

I haven't checked any voltages, is there a separate supply for the actual processing that's different from whatever is saving/recalling presets though?

I can check based on Mr. Huge's posted DL4 power supply schem, but first I've gotta get the knobs off... I've just managed to put some dents in them with pliers. Any tips?

Alternatively, can anyone point to solder points on the back of the board I can test?

[robmay]

Update, I blindly checked some from the back of the board, here's what I found:



Let me know if I should check any other spots. Just to clarify one thing, the lower 3.3V is only pointing to the pins of the pots.

[Processaurus]

I heard of people putting rubber between the pliers and the knobs, to not scratch them.  I just dent mine... Possibly one of those IC puller tools, that are a long U shape and have a little bend at each end to hook under the IC's.

Good luck. I've given up on my 2 busted ones.  I'd cut your losses if the power supply section is working and the factory reset doesn't work.  You messed with doing the factory reset a couple times? You hold down the far left and right foot switches, and plug in the input (to power it on).

[robmay]

Tried the factory reset a few times, no luck. I've heard nothing but bad things about build quality on these. Absolutely amazing machine, just not built to last on tour. Fortunately it's not actually my monetary loss, but I'm so close that I don't want to stop trying now.

[robmay]

Alright, specific fix for the DL4 aside, from my description, does it sound like the replacement EPROM is bad?

Old EPROM: Powers on, lights up, saves/recalls presets, passes audio in bypass mode, doesn't pass audio when activated
New EPROM: Totally dead, no audio passing or lights on, no response at all

To me, it looks obvious, but I'm not sure if there's any sort of initializing thing, or anything that I could be missing. If it is bad, I want to get the return process started sooner than later.

Let me know what you guys think. Thanks!

[greymedicine]

If the unit is partially working with the original EPROM, then I'm convinced the problem must be elsewhere. In my experience, digital IC's don't partially fail. They either work or they don't.

Your best bet is to pull it apart and use an audio probe to find where the signal is stopping.

[robmay]

That's what I was thinking. If I'm getting anything out of this EPROM it must be working, and the issue must be elsewhere. I'll try an audio probe, but I always get lost in digital pedals and anything with this small of a circuit.

Does anyone have a DL4 they can quickly check some voltages on? I'm not sure if the voltages I read from the back are right, they seem low in a couple of places, but I'm not sure how to go forward from there.