Roland RS-70 (same keys across octaves don't work)

[jrfrond]

HI, I checked the cables for continuity and both are good.
inpsected the key beds, and the surface in which they are mounted, also I performed a basic maintenance (cleaning with qtips and isopropyl alcohol)but the failure remains, I also checked both connectors (in the motherboard and in the keys) but everything seems fine.
I contacted roland and the spare IC33 is 15 bucks only...
what probability do you think I have to solve the problem replacing the IC ?

warmest regards
Elias.

For $15.00, it's worth a shot. However, unless you have SMD rework experience, I'd say that your biggest issue will be the actual replacement itself.

[elias]

A video I've found

I've found a video on how to replace those sMD's
Surface Mount Soldering 101 Video

I think I'm going to give it a shot...

Thanks for your help guys.
Elias.

[elias]

I forgot

To tell you:

God bless you all guys.


Over and out..
Elias.

[km6xz]

Try practicing with a old computer board first, it is easy to damage pads on the main board if you do not have the right rework equipment and experience doing it.
To minimize damage, try removing the IC with Chip Kwik low temperature solder.
The matrix decoded can fail but the vast majority of replacements were perfectly good parts according to Roland. I believe it, a great many people jump to the conclusion that a failure is the due to the most mysterious or unfamiliar part in just about any field of repair. When I was visiting the Roland service manager in SoCal one time, this subject came up. He said key decoders are ordered in more than any other semiconductor yet in Roland's own shop he said they only replaced a dozen or so a year, of all models combined. Whenever my newer techs entered a diagnosis of some custom gate array, I always had direct questions as to how he determined that. It was usually "what else could it be?" Some techs, I believe order parts as a way of getting it off the bench and pushing the problem to the parts department. The custom gate arrays are very reliable. As a precaution against tossing a good part, verify that all is working before disposing of the chip, you might need a spare someday.
Millions of capacitors, ICs and transistors are replaced needlessly as the first step in many misguided repair attempts each year.
From experience, keybed problems are highly skewed towards mechanical or electro-mechanical problems in the keybed itself, ribbon cables, or carbonized key contact strips. While you are ordering the IC, add the key contact strips, you WILL need them eventually so why not have them in stock for the same shipping charge.

[jrfrond]

Stan, you are correct, but you must temper that with the fact that, if a component is suspect, in many cases, it will be more cost-effective to eliminate it via replacement than taking the time to troubleshoot it, and that includes IC's. Even the occasional "shotgun repair" is considered legit. However, there IS a difference between those choices being made by an experienced tech and someone who has limited troubleshooting ability. It then becomes an educated guess rather than a shot in the dark.

In the case of the OP poster here (and there is no disrespect intended, just observation), their troubleshooting skills are minimal, and SMD rework skills non-existent. This is a bad combination, because in my mind, there is a very good chance that the problem will wind up WORSE than before, most likely due to incorrect installation, solder bridges, lifted traces, etc. The DIY approach is great, in some cases. Then there comes a time when you are in over your head. No one performs a perfect SMD chip swap the first time around, and perhaps not the second, third or fourth either. All of us who deal with it on a regular basis will remember when we learned. It's an acquired skill set.

[km6xz]

Well, maybe I am just hard core but charging a customer for a $30 part retail and labor to change it when the pins have observable behavior should should tell the tech who knows how something works whether the response is consistent with the stimulus.
Any time a SMD part is replaced, particularly high density, high pin count there is an increased risk of damaging the board and adding ambiguity to the data accumulated. Who is going to pay for the replacement board if there is damage? I know a lot of shops would add it to the bill but that is not ethical and in many states would be illegal. Taking a couple more minutes to change the suspicion to confirmation seems like a good way to increase profits, lower repair bill and speed getting the unit back to the customer.
I know my techs started thinking more logically and analytically after knowing I would ask them to explain why they suspect a particular mechanism of fault due to evidence. A guess or assumption was not good enough so it did not take long for them to start thinking of what evidence there was and how that evidence would be the logical result of the condition they observed.