Thursday, 31 January 2019

Another Electro-Harmonix Freeze

I got another Electro-Harmonix Freeze fairly cheap, it sounded like it had been killed by an incorrect wrong power supply. I took it apart and found that it was a newer revision than I had seen before, the board was EC-D68 Rev C (the last one was Rev B). The main difference I notice was an AK4558 codec instead of PCM3052A.

Freeze Rev C PCB, flash ROM temporarily removed.
Main PCB, LM317 temporarily removed.

There was no sign of life, I found that the series Schottky diode at the 9V input had failed open-circuit and that the LM317 had an internal short between it's input and output pins. The fast/slow/latch mode switch also fell to pieces when the board came out of the enclosure.

I replaced the bad diode with an SS14L (it was the correct size and I already had some at hand) and installed a new LM317. I thought that the LM317 was supplying 3.3V to the DSP and this would fix everything. Instead, the pedal would pass a clean signal but with a clicking sound once or twice per second. I found out that LM317 is actually used as a 1.25V regulator, which is only used for the analog VCC of the DSP56374.

I thought the clicking may be the DSP watchdog timer firing, possibly because it was missing program code, so I removed the flash memory and dumped it. It was a perfect match for the dump I made of the first pedal I repaired, so no problem there.

Measuring power at every IC I found that the 5V rail was high at around 5.9V and the 3.3V supply was sitting at 3.9V. I thought that U5 and U8 (both SOT-89 packages) were also voltage regulators and that maybe they had been damaged as well. I also noticed that U6 is connected to the reset pin of the DSP, and it was resetting the DSP every second or so. My guess is that U6 (also connected to the 3.3V supply) is some kind of voltage supervisor and it is resetting the DSP because of an incorrect 3.9V at VCC.

I found a great picture at freestompboxes (thanks to Steven_M!) showing that on previous version, U5 was 78L05 (5V regulator) and U8 was BA932 (who knows, but from context it has to be a 3.3V regulator).

U5 & U8 on another revision.

The Rev C board in front of me had "BA420" on both chips. Possibly EHX decided to run all 5V parts off of 3.3V, and doubled up on regulators? I don't know.an

To test this out, I decided to remove both chips and apply 5V and 3.3V from  external power supplies.

U5 & U8 removed, external power applied

This set up was a little awkward, but everything work correctly. Current draw looked totally reasonable, 19mA from the 5V supply and 21mA from the 3.3V. No resetting, no clicking, and the pedal could freeze audio in all 3 modes.

Current draw on 5V and 3.3V supplies.

I ordered L78L05ABUTR and MCP1804T-3302I/MB as replacement 5V and 3.3V SOT-89 regulators. I also used 2MD3T2B2M2RE as a replacement switch. This replacement is not threaded for a nut, but recent version of the Freeze don't look like they are threaded either. Pedal works like new.



6 comments:

  1. Hi! i would like to take just the wet signal of the pedal without the dry, do you know how to do it? I thought to take the 2 pins of the pot and send them to a jack do you think it could work ?

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  2. I think this should work, a lot of people have done effects loop mods that worked fine.

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  3. Hi! Thank you so much for this article!
    I've recently got a Freeze EC-D68 Rev-B to repair. It was clicking/resetting or, when correctly working, make some noises.
    I replaced the first Schottky diode on 9V, then the pedal always worked but with to much noise under the signal!
    Thought it was a power supply, so i replaced the lm317 and the 78L05 and increased the filter caps C2 to 220uF and C28 to 10uF .
    Worked for about 5 minutes then silence!
    Now i only have clean signal, no LED or effect whatsoever but i have:
    1,251V on lm317 output
    4,987V on 78L05 output
    3,278 on U5 output

    Can you please help me?
    Thank you so much

    Mattia.

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    Replies
    1. It sounds like the power supplies are fine. It could be a problem with the DSP?

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    2. Thank, you for the fast reply!

      I fear it may be this =(
      Found out that my U6 seem stable, not resetting the DSP. I read 3.280V on the 2 side pins.

      Is there a way to repair this? some sort of factory reset or something i can try?

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    3. I have kind of a similar problem, mine (rev. B as well) injects a 258Hz white background noise even when is un-engaged, i thought it could be the power supply but is filtered and regulated exactly at 9v, something odd about mine is that around and a bit above of the 78l05 heats a little bit, not too much (40ยบ Celsius), but enough to feel the temperature with bare fingers, and to point that something is going on.

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