Peavey CEQ280A repair

[deveng]

I purchased a Peavey CEQ280A off Ebay and it has some issues.  First, a leaking and totally dead Ni-Cd battery.  Second, a broken LCD display.  I found a replacement battery although I had to mount it off the pcb.    I replaced the cracked yellow LCD with a new Crystalfontz (white and grey) LCD.  The only change required was the series resistor, which sets the back light current. 

Now I'm finding strange and intermittent functional behavior.  I replaced the static RAM but that didn't do it.  Supply voltages are good and clean.  So, I may be experiencing some "bit rot" in the EEPROM.    Does anyone have an image of the EEPROM from a good working unit?  I've got an EERPOM programmer. 

Regards,
Jeff

 

[Andy Peters]

I purchased a Peavey CEQ280A off Ebay and it has some issues.  First, a leaking and totally dead Ni-Cd battery. 

(snip)

Now I'm finding strange and intermittent functional behavior.  I replaced the static RAM but that didn't do it.  Supply voltages are good and clean.  So, I may be experiencing some "bit rot" in the EEPROM.    Does anyone have an image of the EEPROM from a good working unit?  I've got an EERPOM programmer. 

I'm less likely to believe "bit rot" in an EEPROM. In nearly 30 years of doing this, I've never seen a verified case of this as the cause of a failure. (Is this a ceramic EPROM with a window? Was the window covered? Was the window exposed to the sun for a few days? If not, I doubt that the EPROM started to self-erase.) That the battery was leaky implies that the PCB may be damaged. First, try a good cleaning with a proper agent (alcohol won't do it).  Then inspect the board for physical damage. Also verify that power supplies are correct.

 

[deveng]

Good information.  I did clean and inspect the traces near the leaky battery.  Voltages are clean and good.    The EEPROM does have the window covered and doesn't look like the label has been removed or touched.  Battery voltage is good to device pins when the unit is shut down. 

The device worked intermittently for awhile when first powered up.  Now it fails function every time.  Some of the menus work (i.e. global settings, display settings, etc)  but when I go to the EQ display, all the levels are at rock bottom and I can't adjust.  Changing frequency works but no level change.

Regards,
Jeff

 

[JohnRoberts]

That's an old soldier... have you tried asking Peavey service?

Leaky batteries have killed many of those era digital products. You are lucky to get it running.

I'm inclined to agree with Andy, the fault is probably not the firmware, could be as simple as a bad connection on one lead of a connection between PCBs.

Customer service may have experience with what the typical failure modes are, while I've heard of many similar units that were "do not resuscitate" after the battery leaks..

JR

 

[deveng]

Have not contacted Peavey about the functional issues.  I did call them about the LCD display.  Factory replacement was over $120!  The  Crystalfonz popped right in for $23.  I figured any replacement IC's would be too much as well.  Although, if their service department is good, they might have some advice on leaky battery issues.  I've already got more money in this darn thing than its worth!  But, now I've got a personal vendetta on it.  I'm not to the point of trashing it yet!

I did a quick check on the traces and they appeared good at the time.  I'll go in again and do a complete investigation on all the traces near the leak.  Repair if necessary. If the battery leaked and destroyed traces, those can be fixed.  But, I'm not clear on what a dead cell battery would do to the +5v IC's as long as VIH was not over the limit above VCC.  Since they'd all be running low that would not appear to happen. It was pulling the regulated voltage down before I replaced the battery.  I've scoped the +5v and it is good.  Runs at a solid 4.97V.

I don't want to complicate my debug!  Common sense says its a bad trace  caused by leaky battery.  I might need to remove sockets near the battery leak to investigate under them.

Regards,
Jeff

 

[deveng]

I rechecked all the connections near the leaky battery.  The traces were good but there was some corroded solder joints, continuity was good though.  I cleaned these points up a bit and as expected the issue remained.  I pulled the EPROM and the static RAM then took a close look underneath the socket and at the leads.  There was some oxidation on all the pins of the EPROM.  Cleaned them up, reinserted and powered it up.  Its been working now for hours with no indication of any functional failure.    If I get lucky, that's all it was.   

Will probably be a good idea to use some vinegar and water on the corroded pcb mounted part leads to neutralize the Ni-Cd electrolyte.  Then carefully rinse clean and apply some baking soda and water, then dry and bench test before putting back into service.  Don't need to do anything to the EPROM leads now as they clean and shiny.

Regards,
Jeff

 

[JohnRoberts]

Congrats... I've heard far more reports of death by leaking battery, than fixes.

JR

 

[deveng]

Arrrrrrggghhhhh!  Problem is back.  It appears to be an intermittent boot-up issue.  It will sometimes boot with the "battery ok" indication and everything works great.  Then the next time I power-up it might show "loading factory settings" and then won't work for crap.    I contacted Peavey and they sent be a terrible and unreadable Autograph II schematic.  They're now working on a cleaner version so I can at least try and debug the battery, static RAM and EPROM connections.  Since it is intermittent, I figure there must be a bad trace or solder joint but I can't find it! 

When I receive the new schematic I'll give it another try.

Regards,
Jeff

 

[deveng]

I don't like when a machine gets the best of me!  I went back in and took another look.  Found a 3.6v zener in the battery circuit that had some nasty solder joints (corroded by leaky battery).  I cleaned them up with vinegar, a rinse and then re-solder.  Also found a very questionable trace running off the battery low side.  After fixing both of these the unit is working again, so far.  I've cycled power (and boot-up) a dozen times over the last few hours and so far so good.  Now its a wait and see if another issue rears up.

Regards,
Jeff

 

[deveng]

Boot up glitch happened again.  But, I think I finally found the last of the board issues.  There's a 3.6V zener in the battery charge/memory reset circuit that had an odd voltage on the anode leg.  I pulled the zener and found a trace/via underneath.  Both were partially eaten away by the battery leak.  Fixed that and its been working correctly for about 4 days now.  I hope that's it.  I'll run it for days, toggle off/on and see if I can break it.  If not, back in service it goes!

Regards,
Jeff

Update 6/9/2016:  Still running perfect.  Looks like problems solved!
Update 7/1/2106:  Unit in service since  6/9 and running perfectly.  Problem is solved.