Roland KC-350 schematic needed

[gui_tarzan]

I've got one in for service and cannot find a schematic for it anywhere. It apparently doesn't power up (no, I haven't plugged it in yet) and I scanned the PCBs for issues. There is a blue cap where the power comes in that is open when I test for continuity. I thought was a MOV, but it's labeled C7 on the circuit board and looks like it's numbered like a cap.

[eniam rognab]

safety capacitor, designed NOT to fail, but in the event of a fail they are designed to fail OPEN. used for input line filtering. either an X or Y cap. X caps go across (get it?) the line and neutral. Y caps go from either line or neutral to ground. this part failing would be most apparent.

hope that helps some, research X/Y caps, interesting reading

here is a picture of one of the units i repair at work, they have super duper discrete line filtering. the bigger ones are the X caps and the smaller are Y caps, that circuit can handle 15 amperes of current

neal

[gui_tarzan]

So if that fails open it'll just not filter incoming power, right? The power connector still connects juice to the board but the owner said it won't power up. One of the sites I went to to read up on these said if this part fails it could allow spikes through and blow fuses.

[eniam rognab]

So if that fails open it'll just not filter incoming power, right? The power connector still connects juice to the board but the owner said it won't power up. One of the sites I went to to read up on these said if this part fails it could allow spikes through and blow fuses.

yup and yup, failure usually blows fuses and rectifiers anyway, at least in my experience... ive seen some nasty 'splosions of those things at work you should have seen the one that got hit by lightning, i dont know why they even bothered sending it to us!!!!

if that cap looks the way it does i would move on down the line. we use a 5 amp switch on a variac to 'low volt' test the units. lightbulb limiter would be best for you AND variac, preferably with a current meter so you can see what is going on. if you start cranking that variac slowly and see a jump in current there is a short somewhere, otherwise if it gets the full 120v and draws nothing start tracing voltages until you hit the bad component.

thats what my method is anyway, not SAFE by any means, but not "banana jack amps" unsafe, unless you dont know what you are doing.... 1/10th of an ampere is enough to kill you

i got a nasty little electrical burn on my pinkie checking heatsinks for temp; my pinky hit that copper ground the bridge is screwed to. -60vDC through just my hand, keep one hand in the pocket or behind back doing these kind of tests. if you are unsure DONT i basically told you how to kill yourself stay alive to play your guitarzan

sounds like a component opened up if you get power to the board, but not that safety cap, check fuses; and diodes for forward voltage/short, gonna be one or the other

BE SAFE!! but have fun too
neal

[gui_tarzan]

Thanks, I'm well aware of all the dangers. There are a lot of tiny parts on this board, I hate that I'm starting to lose my up-real-close vision clarity. It's a good thing I have magnifying glasses. Actually my phone is a big help, the camera is great for up close shots.

No Variac yet but I do have a light bulb limiter. It works great.

[eniam rognab]

No Variac yet but I do have a light bulb limiter. It works great.

check out "circuit specialists" they have variacs for a decent price if that is a hangup, you should have one... just a suggestion, and one of those lighted magnifying glasses that clamp to your table, use mine at work all day!

not trying to belittle you on the safety factor, just wanted to add that stuff for liabilities sake... maybe Gerry will see this thread

no help on a schematic or layout though, sorry, just standard troubleshooting stuff

[gui_tarzan]

Yeah, I know and that doggone banana jack amp is a docket-full of cases just waiting to happen.

Yes, I know I need a variac, I need an oscilloscope too but so far (knock on wood) I haven't needed one. They're on "the list" of things to get as money allows.

I appreciate the tips, I'll check the diodes tonight and see what's what. There are a ton of them in this.

[edit] The diodes and the fuse all check out good.

[eniam rognab]

hey, no problem buddy

re-reading my above post a diode could also read open, indicating its bad, same as shorted, a good forward voltage reading indicates a good diode. just i usually see shorted diodes...

good luck man!