Author Topic: BOSS RC-300 Repair - A sad tale of stupidity in purchasing and repairing. Help?!  (Read 271 times)

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Offline Animadversior

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Greetings all,

Longtime casual viewer, occasional unregistered lurker turned first-time poster here. I used to post on some of the Rush messageboards back in the late '90's and '00's -- But this is my first messageboard post in ages! I bring you a sad tale that begins with a stupid decision made in an excite-induced daydream resulting in a hard lesson learned, has a hopeful middle bit that progresses to a sad climax, and finally the part of the story where you hopefully come in to save me and/or, rather likely, console/humiliate me as I ultimately resign the fate of this saga to its proprietary demise and careful manual reading... As I now fear that I may indeed have been my own worst enemy (from the beginning - clearly - and) right after the middle bit all along.  :palm:

To keep this long saga short (HA!): I picked up a used BOSS RC-300 Loop Station from a local shop in Portland, OR. The salesman was pretty heavy on the sales when I took a look around the small, packed, and dimly lit shop before checking out the pedal. And I should say that I don't do well under pressure in general, especially when dealing with the pushy types. Eventually, I check it out and my eager eyes see the usual guitarist-level encrustment of dirt and figure it looks pretty good. But when I plug it in, the 16x2 character screen is blank. At this point the salesiness intensified and he began checking the power supply and looking for another one... Still undeterred and focused on my dream, I reasoned that the contrast just needed to be adjusted and proceed to look up the manual to figure out how to do so (but back in reality, I know better) while he swapped wall-warts back & forth and agreed with me about trying the contrast. Ah, there it is: nice and easy -- Power off, on, system button, then spin the knob... No response. Huh... - Should have bailed right here - But no, he quips: Factory reset! Hmm. Ok, ok... Found it. Done. And - I'll be damned - it worked! I snapped back into the dream and he left me alone to poke around with an acoustic and check it out a bit. I'm not jamming on loops or anything, I just record something on each track to verify functionality and move on to check the mic input, other outputs, poke through menus and such. It's looking good but then I notice one of the buttons bounce back. Then another. I am more actively suspicious of the unit now, but my daydreaming brain says "Hey man; You're savvy - You fix stuff all the time... You've fixed several effects pedals in the past. Definitely fixed worse than switches in your day and now you work for an electronics manufacturer, so you can easily replace a few tactile switches and then some if you have to. Just dooo it!" (Meanwhile, the dream had washed all thoughts of the screen completely from my mind besides the fact that I was currently looking at it and it was functioning.) After poking around a wee bit more in a vein attempt to diagnose the inconsistent button response, I - very stupidly - decided to just go for it. And so if you count from here, my first mistake was not having enough of an initiative to make the attempt to convince our salesman that the pedal had issues as he was very clear that the factory reset fixed it and everything was fully tested. My second mistake: Not negotiating to that regard (And generally not being the type of person to do this sort of thing in the first place). Third mistake: Paying nearer to the full price of a new unit than that of a clearly used pedal with issues. Fourth mistake: Paying cash. Need I go on? Suffice it to say, I later found out that returning was not an option for me. I was even willing to take a 15% hit on a restocking fee per his return policy, but he flat-out refused. Lesson learned.  |O

The next day, I opened it up to see what was going on in there. Sure enough, a drink of some sort (likely cheap beer from the pungent fragrance it put off during cleanup) had definitely been spilled on the pedal some time ago. Ironically, all of the tactile switches on the board are clearly of a higher IP rating than anything we stock at work. There was some light corrosion on a few jumpers, a couple of LED's for the effects that were around the main ingress points had been rusted to death (I didn't actually notice them at the store due to unfamiliarity with operation/blindness), and the majority of the corrosion was around and under a multiplexer which explained all the switching issues. After pulling some components, cleaning up the obvious corrosion, replaced the LEDs with some green ones on hand, and popping the cleaned up IC back in place; I moved on to cleaning the mild non-IPA residue from the rest of the boards with IPA. Seeing nothing else alarming, I mock assembled the pedal and tested. After passing, I wrapped it all up and headed home.

... And it worked great! I had several hours that evening of practice and fun with the effects. Laid down some grooves to practice soloing over, setup some patches for various rhythms, etc... I was stoked! But it was late, and so it was off to bed. The hopeful bit in the middle. :phew:

The next day - Sunday morning: Power it on - display is dead.  :wtf: Factory reset? Kinda... No... Nope. Blips in & out... And finally went dead.  :-[ Dismantle the pedal again, this time pulling the 16x2 display. I was hoping for easy to clean stripes somewhere in there, but was not so lucky. 8 Pin ribbon cable COG LCD with separate LED backlight in plastic housing (Part number and deduced specs below). After some research I decided to apply some careful heat to the COG module with my hot-air gun. Plugged back into the main-board & it worked again! "So it's a dieing screen." I thought... My reasoning at the time was that some beer-juice hit the ribbon cable and made its way down to the connection at the chip-on-glass. I was oh-so-hopeful that the heat fixed it so I tested and verified it was working before putting it together again and driving the not-even-ten minutes back home. Power it on & get a stomach churning nothing on the 16x2. At this point I've tried enough factory resets to be over that salesman's trick. I went back to work and recleaned the boards but heating the COG module was the only thing that worked. Decided to place it in our hot air oven for well over 8 hours @ 66 degrees celsius. Got home with it and again played for hours. I thought I'd had it lick'd with that much heat and time. But when taking a relatively short break for dinner, I took the risk and turned it off. When I powered the unit back on the display was - you guessed it - blank again. I was crushed (still am). I tried to put it in the oven again and applied some light clamping pressure to the cable connections as the glass cooled... But it also took a tumble at some point there and now there's a tiny chip in a corner. It has not worked since that event. My own worst enemy. :horse:

Fortunately tho (maybe?), at some point when the display was working I did take some measurements with a scope. Unfortunately, I hardly have a smattering of an idea as to what I'm actually doing so I don't completely understand what I'm looking at or what I was looking for in order to decipher what might be going on. I will soon proceed to spew out the data that I have on the display and follow with photos of the signals I saw on the scope. Being the creator of my own favorite headache, I no longer see those signals on the scope when probing, (damaged) display connected or not. My new reasoning is that one of the caps on the motherboard used or the COGs "booster circuit" is wonky... And I'm guessing that if I would have replaced IT before screwing with and breaking the 16x2 screen, then the whole saga might have been over after the middle bit. But instead, I think that heating the COG allowed the liquid crystals to work with the little power that the circuit could give until they finally reached room temperature and got stuck again... But honestly, I have no idea what the booster circuit in the datasheet is doing, nor what I'm doing -- Clearly. I took electronics in high school, but that was ages and careers ago. Being an autodidact didn't work out so well for me when it came to actually understanding electrical engineering. I currently do more hands-on building and process improvements, but I have done some KiCad projects. Still, I have always had a hard time understanding the levels of abstraction and all the technical jargon in datasheets as well as component interaction in general.

I really don't know if I have a chance anymore if I did indeed break the screen. Signals decoded or not, if the cap (or whatever is wrong with the board) isn't fixed first then it's likely not possible to hack a screen into it. I suppose my best bet is finding a for-parts unit, but I don't think I can stomach buying another broken pedal. I don't have any hope for getting help from the BOSS/Roland service department, but might be convinced otherwise if someone knows something I don't.  :-DD >:(  :rant: Buying one of the very few 8 pin screens on the market is certainly a silly gamble, too. Anywho... I will now list what I've found out so far in the last ditch hope that someone can help... Thank you all for your time, advice, and any good jabs or anecdotes you can give to help ease my pain.  :palm: :-// :popcorn:

The screen in question: PE1602MRT-012-I-0 N C 914729059 1416 O

Via the PowerTip website (, I've decoded the part number to be:
M=Amber LED Backlight
R="Standard" Connection type
T=FSTN Negative Black
012=Model Name/Series Number
I=Transmissive/6:00 Viewing angle/Wide Temp
... And the rest of the digits seem to be unique to Roland/Boss.

I believe it uses the ST7032 driver, based on the fact that it is the same one that the 16x2 COG LCD available at PowerTip uses. However, that display has 14 pins in its datasheet. My display has 28 pins at the glass but 8 on the ribbon cable at the board connection. I cannot reckon of all this, the extensive datasheet, and the various communication protocols with my findings.  :-//

TL,DR: I duped myself with help from a shyster and charlaton into buying a used & marinated BOSS RC-300 for way too much money. Cleaned it up and fixed some corrosion only to have the obscure 8-Pin 16x2 display pseudo-die and I now think the flaw is elsewhere & the screen itself was actually fine until I dropped it. I'm here in hopes that I can find help with a fix, replacement, or hack -- but ultimately I suppose some sympathy and/or laughs for another sucker of a shyster and proprietary obsolescence.

I will follow this post with my oscilloscope findings. Thanks again for tagging along with this post...  :-+
« Last Edit: August 04, 2021, 04:52:23 am by Animadversior »

Offline Animadversior

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Pin 1: 3.3V - Could be Reset? 
Pin 2: Some sort of Data line
Pin 3: Another sort of Data line - looks.... Broken?
Pin 4: GND (No Photo)
Pin 5: 3.3V - Power?
Pin 6: 6.4V - Related to that booster circuit?
Pin 7: 3.3V-6.4V Square wave.
Pin 8: 0-3.3 Square wave.     

I really hope I can at least hack something into this, otherwise I'll just start practicing visualizing the display in my mind while reading the manual and pressing buttons.   :-+

Offline bob91343

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Your sad story made me chuckle, as I have more or less gone through similar situations.  I offer no help; in fact I would like to have some.  I suspect I have ruined a few things that I could have repaired.

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