Line 6 FM4 startup issue

[stevenrb718]

Anybody have any thoughts on FM4 that won't kick on? Had a short on the 3.3V line that located to the 56364 IC at U2. Replaced the IC and seem to have proper voltages throughout with the 3.3V, 5V, and 6.6V, but pedal still won't click on. Any ideas?

[Steve L]

The usual issue (over fifty percent of the time) with those devices is the EEPROM connection.
Carefully remove the EEPROM located on the back of the board, check for any damage to the pins and socket first, repair if needed, and then put it back in and try powering it again.
There is usually no damage. Just the contact wiping action of removing and re-inserting the EEPROM is enough.

If that will not solve the problem, check that either of the caps next to the crystal are not shorted.

These two "fixes" and a few issues with the power supply that you have appeared to correct will fix 9 out of 10 of those devices.

Steve

[stevenrb718]

I must have a 1 out of 10 unit then, haha. The EPROM socket has continuity on all the pins, and the EPROM itself does too. There are no more shorted caps anywhere on the board since repairing the 3.3V line.

[The Dude]

The usual issue (over fifty percent of the time) with those devices is the EEPROM connection.
Carefully remove the EEPROM located on the back of the board, check for any damage to the pins and socket first, repair if needed, and then put it back in and try powering it again.
There is usually no damage. Just the contact wiping action of removing and re-inserting the EEPROM is enough.

If that will not solve the problem, check that either of the caps next to the crystal are not shorted.

These two "fixes" and a few issues with the power supply that you have appeared to correct will fix 9 out of 10 of those devices.

Steve

I've run into that several times, too. A couple times, just removing and reseating the EEPROM didn't work. I had to actually take a very small jewelers screwdriver and carefully retension the socket pins for the EEPROM so that they made better connection to the chip.

[g1]

The EPROM socket has continuity on all the pins, and the EPROM itself does too.

Just want to verify you tried the remove & re-install anyway? Sometimes continuity can read ok when non-powered but not hold up under power.

[The Dude]

Yes, and sometimes just putting a little pressure on the socket pins with your probe is enough for it to make a temporary connection. I (now) just retention the socket pins every time to make sure they make good connection. IMO, it's a more reliable fix over just reseating the chip.

[stevenrb718]

Just want to verify you tried the remove & re-install anyway? Sometimes continuity can read ok when non-powered but not hold up under power.

Yeah I've pulled it out dozens of times and pushed it back in place in different levels of seating. I feel like the issue is beyond the EPROM or the socket.

[g1]

Can anyone post schematics or service manual?

[Steve L]

Here is everything that I have.

Line 6 DL4, MM4, FM4 Service Manual.pdf
Line 6 DL4, MM4, FM4 Test Procedure.pdf
Line 6 Troubleshooting Guides.pdf

At this point in his repair, an oscilloscope is needed.

Steve

[beedoola]

There uses to be a guide somewhere for checking all the PS voltages.

did you try doing a factory reset with the footswitches when powering it on? I’ve had to do that as part of the reset/resurrection process of these before. Especially after reseating the EPROM.

Also, did you clean the EPROM pins and socket with contact cleaner after pulling the chip? I just did this with tjr EHX POG that wasn’t working right and that fixed it.

[stevenrb718]

There uses to be a guide somewhere for checking all the PS voltages.

did you try doing a factory reset with the footswitches when powering it on? I’ve had to do that as part of the reset/resurrection process of these before. Especially after reseating the EPROM.

Also, did you clean the EPROM pins and socket with contact cleaner after pulling the chip? I just did this with tjr EHX POG that wasn’t working right and that fixed it.

I haven't seen a guide for the test voltages. I've already done everything with the EPROM with no change.