Line 6 Echo Park

The other Line 6 green delay. The ToneCore series was released around 2004, after the larger 4x4 stompbox modeller series. The series looks like they were intended to be small factor versions of models from the previous series, the Echo Park is something like a refined DL4, smaller and cheaper and shares a lot of the same delay models. It has the advantage of running off a standard 9V supply but omitted the looper that made the DL4 such a success.

Echo Park

In an unusual design choice, the pedals are split into two components, the "dock" (containing the main chassis, DSP, switches, jacks, power supplies and input/output buffers & amplifiers) and the "module" (holding the knobs, switches, a microcontroller and the program code for the DSP). This is the same idea as the DL4/FM4/MM4 series using the same PCBs with different program code, but allows different pedals to have different numbers or types of knobs and switches instead of shoe-horning everything into one shared format.

Modules and docks were sold separately and marketed as interchangeable. Red Panda even made a third-party module. Line6 released a programmable Developer's Kit module in 2008 that allowed hobbyists to create DSP effects that ran on the platform. This is a very cool idea but it doesn't look like it ever took off, there are very few examples online of anyone actually building anything.

This Echo Park was bought used and needing repair. The LED would flash once on when power was applied, but it was otherwise completely dead. I was hoping that I could easly isolate the problem to either the module or dock.

Unlike the DL4, there are no service manuals online. However, Line 6 did publish a ToneCore SDK Hardware Guide which has block diagrams and some slightly blurry schematics for the dock and the programmable Developer Kit module. The Developer module is not the same as the product modules, but it should be close enough to make repairs possible.

 ToneCore Dock

Dock, backside. Note test points.

Dock PCB, topside.

The insides of the dock look familiar, there is a DSP56364 dsp and some power and analog stuff. I managed to connect the dock and module together lying flying flat on my bench using some right-angle headers and some jumper wires so I could probe the signals between them. I was getting power and some of the clock signals were present, but I couldn't see any signs of the module programming the DSP when applying power (as the module contains the "effect", the DSP code must be stored there and transferred to the dock on startup).
There are testpoints on the backside of the PCB for MCU, DSP and ADC/DAC clocks, this is the place to look with an oscilloscope if you are debugging one of these.

Negative voltage generator

One interesting feature of this series is that they were the first (possibly only?) Line 6 pedal to run with a standard 9V DC supply instead of shipping with a bulky AC supply. The dock uses the 9V power and one of the clock signals from the DSP to form a curde charge pump to create a negative voltage rail of about -7V. This is pretty smart! I'm surprised it isn't more common in digital pedals.

Echo Park Module

Module PCB, as found

After opening the module it was pretty clear that someone had been in here before. Some traces were damaged and a SOT23 package device (Q1) was missing. A red jumper wire has been added. There are a lot of similarities with the schematic in the SDK manuals, the MCU is different (it's a P89LPC935F, an 80C51 derivative like in the 4x4 pedals) and the product modules add an SST25F512 SPI flash memory chip but otherwise it looks close enough to use as a reference for repair. The manual schematic shows that the missing SOT23 package is a PMBT4401, I didn't have one at hand but I did have some BC847C that should be a good alternative. The schematic also had enough information to replace the damaged traces with some jumper wires after beeping things out with a DMM.

After repair attempts. One of the switches was removed temporarily to help with following hidden traces.

So I added transistor and the jumpers, and... nothing. Just one short LED flash when it's powered up and nothing else. I suspected either the flash memory or the MCU in the module were bad, but the MCU was now expensive to replace and difficult to source, and I had no copy of the contents of the memory so there wasn't much that could be done. So this went back into the box and into the "fix" pile and stayed there for a year.

Second attempt:

 

The line-up

Eventually I got two more non-working Echo Parks to look at from Moose Electronics. Maybe I could mix and match modules and docks to figure out which were good, maybe I could even fix all three. I labelled these to keep track, mine is #1 and the new ones are #2 and #3.

Starting out, none of the pedals worked. The immediate good news from swapping parts was that my dock (#1) worked with the modules from #2 & #3. No other permutations gave me a working pedal, so I knew my module was bad and docks #2 & #3 were bad. I opened the bad docks and one of them had a battery cable pinched between some header pins and sockets. Nothing else looked obviously bad. When I tested it again it worked perfectly. Either moving that cable or reseating the header pin/socket connection must have restored power.
The other bad dock had no obvious damage, and looked like it had a dead DSP. None of the test signals on the backside of the PCB were present, and they should be generated by the DSP, which did have power. In this case it's actually cheaper to buy a less desirable ToneCore pedal just for the dock than attempting to swap out the DSP, so this Echo Park will be getting a replacement instead of a repair.

This just leaves my bad module, #1. Suspecting the serial flash or the MCU, I decided to desolder the serial flash and see if it could be read in my programmer, and what data was on there. The chip ID was correctly identified, but the contents were all 0xFF! Effectively this was blank and there was no program code for the pedal to run. I pulled one of the flash chips from one of the working modules and dumped it, and re-programmed the empty chip. After resoldering it, the pedal lit up and worked just like the other one. I can only assume that the soldering "accident" I saw either caused the memory to be erased or was an attempt to fix it, I can't be sure.

Desoldering U1

Dumping U1

So, if I had had a memory dump of this a year ago I could have fixed my pedal then. In the interest of helping someone out, here is the contents of the flash.