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ROM issue Digitech DSP 256XL
ROM issue Digitech DSP 256XL
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Old 23rd March 2011, 12:01 AM   #1
oshunANDurth is offline oshunANDurth  Australia
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Join Date: Mar 2011
Default ROM issue Digitech DSP 256XL


If this isn't the right forum, I apologise and can someone please let me know where I should post this.

I have a Digitech DSP 256XL that's worked fine for years but now when I turn it on the error message 'ROM Test FAILED' appears on the LED screen.

Guess I need to know what the issue is and if I can fix it.

If I end up fixing it, I'd also like to service the unit so any advice on that would be great too.

Would rather cut off my right nut than lose this thing so any help greatly appreciated.

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Old 23rd March 2011, 01:55 AM   #2
wakibaki is offline wakibaki  United Kingdom
Join Date: Jan 2008
It doesn't sound good. I don't know this device, but from general knowledge of digital...

The ROM is where the program or at least the program loader is stored. It's commonplace for devices to have a POST (power on self test). One of the first things it's likely to do is treat all the memory as numbers, add them all up and compare them with a number, probably stored in the last memory location. Yours is failing that test in all probability.

ROMs are often EPROMs, which are erasable using UV light, or EEPROMS, which are electrically erasable. Sometimes they fail with time or use.

There is a small possibility that just some or one of the connections to the ROM has failed. If you can identify it you could try resoldering the pins. If it's an EPROM it will have a window in the top covered with a sticker and it will most probably be socketed. Otherwise you can look up the part numbers of all the chips in the device on the web. You can even resolder every pin on the board, but I don't recommend this, particularly if the chips are surface mount (not thru hole). It's easy for an inexperienced person to leave a solder string which might damage the device beyond economic repair when powered-on.

If the ROM is corrupted and failing the POST for that reason, there is no alternative but to replace or reprogram it. It may be possible to reprogram it in situ, but it may not.

It is unlikely that any repair shop will be able to help you, pretty much the only thing you can do is return it to the manufacturer to fix.

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Old 23rd March 2011, 03:11 AM   #3
oshunANDurth is offline oshunANDurth  Australia
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wakibaki you are a deadset legend! I just looked for the EPROM, pulled it out and re-inserted it and now the unit is working perfectly. I must have bumped it or something. Cheers for your help!!!
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Old 24th March 2011, 06:30 AM   #4
qusp is offline qusp  Australia
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Location: Brisbane, Australia
its also possible that some static charge built up on the pins and was disrupting its proper operation; when you pulled and replaced it you cleared this charge and all is well. i love a happy ending and almost without any tears. i'm sure your right nut is thankful for the respite
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Old 26th March 2011, 07:14 AM   #5
oshunANDurth is offline oshunANDurth  Australia
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Join Date: Mar 2011
Yeah, I'm pretty sure I heard it breathe a sigh of relief.
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