Need GR-20 Fix Help

Started by edbub, March 31, 2016, 05:45:27 AM

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edbub

Hello good people! I've got a GR-20 that, when powering up, displays "8.8." and will do nothing more. The front panel is dead; can't do a factory reset. It almost appears that the boot sequence never executes. I've looked all over the internet for a schematic or service manual.. nada. My suspicions lead me to believe that I should simply start by checking the voltage levels on the board(s), but I've got no reference point. PS - I know the wall wart/power adapter is good. If anyone has any thoughts, suggestions or direction to give - I'd appreciate it! Thanks!

HAMERMAN409

I haven't seen a service manual for the GR-20 so I don't know what they are using but if you can post some high res pictures somewhere we should be able to figure out what they are doing so you have somewhere to start.

I have a very poor quality service manual for a GR-33 and that uses linear regulators to make Digital +5V and +3.3V and analog +7V and -7V. The GR-20 is new enough that there is a good chance they are using a switching supply, if you can figure out what IC's they are using we will have something to go on. They would usually be near the power jack and would have some capacitors, diodes  and an inductor nearby.

Based on the "8.8." on the display I would suspect that the higher digital supply voltage (+5V or 3.3V) is good and that the lower digital voltage (+3.3V or +1.8V) is bad - but that is just wild guessing.

Elantric

#2
If you fire up the soldering iron and inadvertently start attempting a repair , Without any GR-20 Service Notes or documentation, you can easily turn a $75 repair into a $300 repair bill.

find a local Roland service center
http://www.rolandus.com/support/service_repair/service_centers/

Contact
Roland Corporation U.S.
5100 S. Eastern Ave.
Los Angeles, CA 90040-2938
Customer Service Tel: (323) 890-3700


edbub

Thanks for the replies guys! There are clearly three regulators on the board, as you can see in the photos. I will throw a DVM across these and see what gives. Interestingly enough, there is a V7330 Panasonic device in there that is a surge arrestor. Going to have a look there as well. Keep those ideas coming!

edbub

All three regulators appear good - at east there is output. I'm seeing -5, 7 and 9v. I moved deeper into the board and tried to measure input voltage at an op-amp. Nada. I'm trying to figure out the surge suppressor, and where it connects in the circuit. It's almost like the regulators are working, but there is something between them and the rest of the logic board that is preventing it from becoming energized. One would think this surge supressor would be across the input though. It measures open with an ohm meter. The good news is that it appears to be power related, and not the brain. Should be fixable!!!

Elantric

#5
Check Electrolytic Capacitors, and compare to the typical power supply design Roland employs for similar products 
http://www.synfo.nl/servicemanuals/Roland/GR-30_SERVICE_NOTES.pdf

gumtown

Is there an internal button cell lithium battery ( Roland ones of that era are typically a CR2032).
If there is one, It may be flat.
Remove and let the memory discharge for half an hour, then install a new cell.
Free "GR-55 FloorBoard" editor software from https://sourceforge.net/projects/grfloorboard/

edbub

I'm afraid there is no battery - I've taken all teh boards out - nada. So, I kind of screwed up in that when I was measuring voltages to the IC's, I was using a crappy ground. There are Vcc voltages. I have to break out an oscilloscope and look for any ripple tho.. that's my next step sometime over the weekend. I appreciate all fo you guys sounding off on this!

edbub

Update - no farther along. I am fairly certain the power supply is good at this point. I may reach out to Roland and see if they would offer some sort of flat fee estimate - and factor that in on my next move. Ugh