RC-20 Repair Info

[.Mike]

A guy on my local Craigslist had a broken RC-20 for $40. I emailed and asked him if I could have it if he didn't find a buyer. It's mine now.

Generally, I'm looking for any documents that anyone might have for the Boss RC-20.

I was told that the batteries had leaked into the unit. It appears as though it leaked when sitting in the proper position, The only corrosion is on the back plate, with no visible damage to any of the electronics.

I have only looked at it briefly. It passes sound. I am leaning towards it being a fried power supply component. When I power it up on either batteries or an adapter, I get a dim Power light, and full-brightness Reverse, Tap Tempo, Loop Quantize, Write, Phrase Used, Normal, and Flat Amp Simulate lights. The buttons/knobs do nothing beyond the instrument level knob.

When powering it with a 9V, 350mA adapter that measures 16.25V unloaded, the voltage at the input jack drops to 6V! Something seems to be chewing up a lot of current.

Another interesting thing is that if it is on an I want to cycle the power, I have to unplug it and let it sit for about 40 seconds before powering it back up, or else it will only light up a dim Power light.

Anyway, if anyone has any documents on this unit, or any pointers on where to look, I would appreciate it.

Mike

[.Mike]

OK, you can disregard this. It's dead.

I opened it up and traced the current draw to one of the circuit boards. It was protected by a copper/plastic bottom piece and a metal top shield that were soldered in place, so I removed them. I powered it up, and within 3 seconds, I noticed that a 2cm x 2cm, 144-pin surface mount chip with Boss labeling was so hot that it seared my skin. I can't see how anything could survive that heat for long, and it had definitely been plugged in for more than 3 seconds.

I can't find any details on the chip, and I doubt Boss sells replacements, as if I could solder in a replacement.

So unless someone here happens to have the middle board from an RC-20 stashed away in a box in their closet, or unless a broken unit comes up for cheap on Ebay, this enclosure appears to be destined for a tap tempo tremolo or a double delay. 

Mike

[newfish]

Couldn't have been a heatsink?

Unlikely, given the 'digital' nature of what you've described.

Still, at least you have a decent housing - and some spare pots / BOSS switches.

I guess modern effects are getting like cars - there's very little you can actually 'do' if things go wrong - without the diagrams and diagnostic tools. Oh well...

[DavenPaget]

OK, you can disregard this. It's dead.

I opened it up and traced the current draw to one of the circuit boards. It was protected by a copper/plastic bottom piece and a metal top shield that were soldered in place, so I removed them. I powered it up, and within 3 seconds, I noticed that a 2cm x 2cm, 144-pin surface mount chip with Boss labeling was so hot that it seared my skin. I can't see how anything could survive that heat for long, and it had definitely been plugged in for more than 3 seconds.

I can't find any details on the chip, and I doubt Boss sells replacements, as if I could solder in a replacement.

So unless someone here happens to have the middle board from an RC-20 stashed away in a box in their closet, or unless a broken unit comes up for cheap on Ebay, this enclosure appears to be destined for a tap tempo tremolo or a double delay. 

Mike

The chip most likely failed shorted-out , any pictures ?

[crane]

It IS possibly to buy replacement ICs for boss - you just have to look them up in china ic market - I have repaired a boss reverb that way.
BUT -
1)you have to be able to do smt soldering
2)you have to realize that the IC might not be the only fault - causing a short circiut it might have killed some voltage regulators, may be something else as well

[ugly_guitar_guy]

Which IC is it? I can see if we have them available.

(FYI, if the main board is fried, they're $175 complete, and in stock)

[.Mike]

Couldn't have been a heatsink?

It wasn't a heat sink. I thought that too before I removed it, but the metal shield wasn't in contact with anything. There was about 1/8" between the top of the chip and the metal shield.

The chip most likely failed shorted-out , any pictures ?

Nope, but I could take some. The chip itself looks to be in fine condition. Applying any power to it causes it to instantly heat up.

It IS possibly to buy replacement ICs for boss - you just have to look them up in china ic market - I have repaired a boss reverb that way.
BUT -
1)you have to be able to do smt soldering
2)you have to realize that the IC might not be the only fault - causing a short circiut it might have killed some voltage regulators, may be something else as well

Heh! It's a 144-pin chip that measures 2cm by 2cm. That is certain failure for a first time SMD'er. Plus, you're right-- I doubt the IC is the only part that went bad. I was able to test the power supply board the best I could, and found that it creates a good 1/2 supply when not loaded by the mainboard. But hook up the main board, and it pulls twice the current it is supposed to pull, and drops the voltage way down. I haven't found the regulators yet, but I'm looking.

Which IC is it? I can see if we have them available.

(FYI, if the main board is fried, they're $175 complete, and in stock)

It is labeled BOSS R02780089 D703102A-W05 0244KP018. It's been discontinued (it's the straight RC-20, non XL), so I'm not sure if it would be worth it to fix it at $175. It looks like they go for between $75 and $150 on Ebay.

Thanks guys. I'll take pics this afternoon.

Mike

[.Mike]

Alright, here are two shots of the board (one in the sun). The suspected bad IC is the one on the far right.





As you can see, everything looks good.  

Mike

[ugly_guitar_guy]

It is labeled BOSS R02780089 D703102A-W05 0244KP018. It's been discontinued (it's the straight RC-20, non XL), so I'm not sure if it would be worth it to fix it at $175. It looks like they go for between $75 and $150 on Ebay.

Thanks guys. I'll take pics this afternoon.

Mike

Actually, we can still get IC1 (it has to be ordered from Japan. 2-3 weeks arrival) but it's not discontinued. It's part # F517912901 and it's $44.90 retail.

Can't return it though if it's not the problem, but hope that can still give you some hope!

[.Mike]

I meant the RC-20 itself was discontinued, in case it made a difference to the more current (but apparently now discontinued) RC-20XL.

Thanks for looking into this for me. I'm not so sure a $45 chip to save a $100 (used) pedal is my best bet for getting started in SMD. And like you said, no guarantees on if it fixes it, of course. Without being reasonably sure it's not going to fry as soon as I power it up, I think my dollars are better spent on other projects.

I do have a friend coming into town for Thanksgiving who is the head EE at his company. I'm going to have him take a look, and if he thinks he could replace the chip (or have one of his junior engineers do it-- they burned my PIC LFOs  ), I might PM you.

Thanks!

Mike

[ugly_guitar_guy]

I meant the RC-20 itself was discontinued, in case it made a difference to the more current (but apparently now discontinued) RC-20XL.

Thanks for looking into this for me. I'm not so sure a $45 chip to save a $100 (used) pedal is my best bet for getting started in SMD. And like you said, no guarantees on if it fixes it, of course. Without being reasonably sure it's not going to fry as soon as I power it up, I think my dollars are better spent on other projects.

I do have a friend coming into town for Thanksgiving who is the head EE at his company. I'm going to have him take a look, and if he thinks he could replace the chip (or have one of his junior engineers do it-- they burned my PIC LFOs  ), I might PM you.

Thanks!

Mike

Yeah, tough call to make for sure without knowing what's making that main IC burn that bad. If you want to pull the trigger just let me know!