FAO Clint Sharp...

[Mungo "Two Sheds" Toadfoot]

...and others wot know about Roland keyboards/power supply boards again.

Here's some piccies...

there identifiable as a potential reset-causer?

Si

[Mungo "Two Sheds" Toadfoot]

Oh, in picture 2 there's what I assume to be a cap that's covered in some kind of plastic. I'm also assuming it's covered because it's next to the transformer and might get hot? If so I suppose it's fairly likely it could have failed, but how to tell?

Si

[dennis]

Post some close ups of the solder side so dry joints can be spotted.

[dennis]

The one next to R17? in pic 4 looks more interesting. There doesn't appear to be a need to put resin on them but there looks like there may be some.

[Andrew Gabriel]

In picture 2, at the back, there's a component lead just visible with some charring of the circuit board. In picture 3, it looks like a 180ohm resistor, but the leads and board aren't visible. That could be a thermal/dry joint candidate.

Need to see the underside of the board for any charring and quality of the soldering.

[Andrew Gabriel]

I missed picture 9 first time - It's R14, and it does look like the board might be charred around it or the transistor on the heatsink next to it (BD ?43B).

[Mungo "Two Sheds" Toadfoot]

This squidgy-looking black thing here, next to the brown cap.

Si

[Mungo "Two Sheds" Toadfoot]

It must be very difficult diagnosing faults from photos :)

No, there's no charring on the board at all, despite appearances from my not-good photos. I've re-soldered everything which looks even slightly suspect underneath, even though there was nothing at all which made me think "That's the problem". I sucked all the old solder off the joints and re-made them at the correct temperature, i.e. the new solder flowed properly.

Thing is, I've seen dodgy joints, burnt boards and damaged components in the past so I do have an *idea* of what to look out for, but I've no clue how circuit boards work so I'm unable to look at a component and know that it could cause the problem. They're Italian boards too. Great.

I'll take some underside pics soon, just in case I've missed something.

Si

[Andrew Gabriel]

Looks like a shrink wrapped component, probably an inductor where the shrink wrap would be keeping it wound.

[dennis]

Nope. Its bottom center of

front of the two electrolytics.

It may just be something that has dripped on the components but its hard to see.

[Mungo "Two Sheds" Toadfoot]

> In front of the two electrolytics.

Ah right. No, that just looks like some kind of varnish. They're not as "lumpy" as they look.

Si

[Clint Sharp]

In message , "Mungo \"Two Sheds\" Toadfoot" writes

Yes. In project3.jpg I'd suspect the leftmost brown capacitor inside the aluminium heatsink but if I suspected on I'd change them all. They're cheap enough that I'd consider the time taken to remove and test them all more expensive than the cost of the parts. Basically, that heatsink is an oven for cooking capacitors.

In project2.jpg the heat-shrink covered part to the left of the obvious capacitor is also likely to be an electrolytic capacitor as well but check the board designation.

In project9.jpg be very wary of everything to the left of the yellow covered transformer, that's the non isolated side and it will bite you if there's charge left or it's plugged in.

I take it from your e-mail address that you're not in the north-west?

[Mungo "Two Sheds" Toadfoot]

Thanks, Clint. I'll see about making another list of capacitors and then find out what Maplins has to offer. There used to be a good components shop in Ramsgate but he went yonks ago. As I recall it was the big 'uns that I had trouble finding.

Heh. About as far from the North-East as you can get without drowning.

Thanks again for your help.

Si

[Mungo "Two Sheds" Toadfoot]

...And the NW too, obviously.

*Slaps head*

Si

[Clint Sharp]

In message , "Mungo \"Two Sheds\" Toadfoot" writes

Forget Maplin, use either Farnell or RS, both will deal with private individuals. Farnell have a minimum order which may make them too expensive unless you can find other stuff to buy, if you have a local RS trade counter go and open an account (it's a paperwork exercise if you're going to pay with cash or a card) and they'll post on anything they don't have in stock for free.

rswww.com

Make up a list of the caps and I'll translate into part numbers if you like. The dimensions of the larger capacitors would be useful.

[Mungo "Two Sheds" Toadfoot]

I've ordered them all from a nice chap (hopefully) on ebay now. The resistors are being a bit of a nuisance though. I thought I'd replace the bigger ones, just in case, and they are whoppers. One's [finds resistor calculator because forgotten value] 220 ohms but about an inch long. Seems there's lots of 1/4w ones about. No idea what wattage this one is! How do you tell?

Si

[Clint Sharp]

In message , "Mungo \"Two Sheds\" Toadfoot" writes

Probably no need to replace the resistors if the PSU is working, a simple multimeter check will tell you if a resistor's faulty or not in almost every case.

Experience generally although you can (simplistically) calculate the wattage required by measuring the voltage across it then dividing voltage squared by resistance. Round up to the nearest standard wattage. I suspect that the 220R one you mean isn't original though if it's the one near the heatsink. Looks 'wrong' to me.

[Mungo "Two Sheds" Toadfoot]

Well, it's working so they can stay then. The caps though, are going. They're old anyway so I'm thinking that years of heat cycling can't have been good for their general health. The metal of the keyboard frame under the PSU is quite discoloured through, I'm assuming, heat. I wonder if it would like a little fan in there?

Si