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Long Shot - Roland HP-230 service manual

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Got my hands on a Digital piano for free. A Roland HP-230.

 

It's got a few keys not working. I've metered it out as best I can without a schematic and service manual. What I'm finding is that I'm getting 1.3V to the supply rail on those faulty keys, when working keys have 5V.

 

I've traced the circuit as far as I can, but now it's hit the mainboard and it's what we call a PITA to sort out the hoo-ha on there without some reference.

 

I could do it, in the end. But sometimes it's just nice to have a document in front of me telling me "Put meter here".

 

I found the HP-335 manual easy enough. It's keys are the same, but the mainboard is too different for the manual to be useful.

 

I've verified that it's not the contacts causing the issues. So, got that going for me, which is nice.

 

But it's also interesting that it's exactly every 8 keys that don't work. Tells me it's a common fault rather than contacts.

 

(Bus somewhere?)

 

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Possibly it scans the keyboard similar to a computer one.

 

e.g. the C64 has a pair of CIA chips. Write the row on one, read the input port on the other and get keypress returns for each column on that row.

Repeat for other 7 rows.

Every 8th key faulty probably means either an input or output is faulty. Since you know there's voltage drop occurring I'd guess a faulty output (row select).

 

A quick search indicates this kb was made in the mid 90s - every chance they don't bother using PIA, CIA equivalents and probably have a single chip that handles practically everything including sound generation.

Kb scan might be by dedicated pins or they might use an external multiplexor IC to reduce the pin count.

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It's not a scanning issue. 1.3V on a 5V rail. And I'm having a hard time tracking it down in places. Mainly because I'm being lazy! (HOORAY for lazy).

 

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