Roland Juno 2 Power On Failure

[Ricoche]

Hi everyone,

I started a new topic on this as the other one by a different person "Roland Juno 2 Won't Power On" has been solved. I believe my problem is different.

I basically have a Roland Juno-2 that has never been opened. I open a lot of synths and I can tell I'm the first one to crack it open. The Juno-2 is in excellent condition all around. When you flip the power switch it's completely dead. No flicker, no heat, nothing. It's like the power doesn't even get to first base. I do try to repair my own synths, however I usually leave the Power supply area alone. Inside the Juno-2 seems pretty basic, so I thought I would scout around and see if I could find the problem.

I opened up the synth and inside everything seemed clean and connected. The power cable was fine, the switch looked good, along with everything else...BUT... the Electrolytic Capacitors looked funny to me on the Power Supply Board. Usually if they are bad I notice a bulging at the top, however the three capacitors on the power supply board look fine on top. The bottom however look like they could either be leaking or perhaps surrounded by a glue of sorts. I'm not sure which, although my guess it's a leak. It's kind of dull and crusty while glue is usually shiny and smooth.

My thoughts are that if the Electrolytic Capacitors are bad, that might be the reason the Juno-2 is not turning on, OR getting power to the rest of the synth from the Power Supply board.

Any ideas would be greatly appreciated.

Here are some photos.

[garranimal]

The material on the capacitors may be adhesive. Big caps like that can be knocked loose in transport so it is common to see adhesive used to provide some structure. I would look at the fuse first. If not that, then check continuity on the switch while unplugged.

[Ricoche]

Hello!

Thanks for the reply.

I dug out my other Roland Alpha Juno 2 which is working 100%. I removed the power supply board and swapped it with the one in the non-working Juno-2. It still wouldn't power on which eliminates the power supply board as being the problem. I also put the power supply board from the attached photo into the working Juno-2 and all worked just fine.

I'm now thinking the problem "might" be where the on/off switch is connected to two wires, a brown and black one. With my working Juno-2 both wires are solidly attached and soldered in there very well. With the broken Juno-2, the bottom black wire is pretty solid, but the top brown wire is still attached, but barely. I'm going to warm up the existing solder and try to better connect that top wire. Power isn't getting into the synth at all. Perhaps that's because either the power switch or the connection between the switch and the switch board is at fault. Unfortunately I can't remove the transformer and switch board without desoldering the two wires connected to the on/off switch. Otherwise I'd swap that with working components from my other Juno-2.

I already swapped the fuse for a new one which didn't do anything. Thus that was eliminated from the puzzle.

I'll update my post after re-soldering the wires. Thanks again!!

[Ricoche]

I think I'm going to need a new switch. That could be the problem. The plugs are very loose on the back of the switch which are soldered to the two wires. They wiggle. On my working Juno-2, both the wires and switch are solid. There is no play at all. I don't know, the wiring just looks shoddy to me.

Here is a photo.

[Yekuku]

To test the switch , use a multimeter and test continuity while in "ON' position. ( the synth should not be connected to the mains)
If it works ok then power it on and test the input and output of the power transformer and you should be able to determine the fault.

[Ricoche]

Hello!

Thanks for the replies.

I believe it is the Transformer. It doesn't look blown, but I think it is.

I have replaced the fuse, power supply board, on/off switch, and have checked continuity on the main PCB board and fuse board which is attached to the power switch and cord. What sits in between the Power Supply board ( which is 100% working ) and the fuse board ( 100% working ) is the Transformer. I'm not quite sure how to properly test that, but it seems everything works on the Juno-2 except the Transformer. I mean I have been able to test everything by swapping boards around with a working Juno-2. The only thing I can't test or swap is the Transformer. Perhaps that is my problem. It just has to be. I can't think of anything else....laugh.

Here is a photo of the Power Transformer in my Juno-2.



Thanks everyone!

Jim

[synthparts]

I have seen bad 2-prong power jacks and even faulty power cables, you sure those aren't it?

[Ricoche]

I have seen bad 2-prong power jacks and even faulty power cables, you sure those aren't it?

I checked that, but I'll check again. I'm going over everything again this evening. Thanks for all the help everyone. Much appreciated.

[Dr. Phibes]

Horrible when these things don't work when everything seems to say they should.

Try to do a continuity test across the blue and white wires that connect to the primary winding (power OFF!). Do the same across the orange and yellow pairs that come off the secondary winding. It's a bit crude but if you find an open circuit you'll know for sure that some sort of fault has arisen.

Although, if I'm not mistaken the transformer looks like it's bolted on so maybe you could just try swapping it out too. Fiddly I know, but you can just about do it if you can get a firm grip on the inner nut (maybe with some pliers) whilst you turn the screw. Or are they one of those God-awful machine screws normal screwdrivers don't work with?

Failing that, you could check that big molex connector coming off the transformer. Those can sometimes break too.

[kottis]

I am having the same issues with my Juno 2. Have you managed to get the power on yet?