Roland JC-77 Power Transformer....Replacement?

[acorkos]

power goes in, but nothing comes out. any ideas as to where i can get a replacement/substitute transformer? it says 30V-0-30V on the secondaries connecting to the main PCB:

[Enzo]

Furst thing is ask Roland...

Yeah, I know that is pretty funny. 30-0-30 is 60v center tapped. and 159 VA is 158 watts or about 5 amps. SO most any tranny that spits out 24-30 volts a side at that sort of current would do.

What I would do:
Call Peavey and ask if they have any of the following power transformers in stock. Here is part number and model it served:
70516743 - 260C power amp
70518714 - 260D power amp
70518713 - Bandit 65
70516734 - Special (Verify this is not a typo for 16743 on the schematic)
70518714 - Special 130

All these transformers produce 42 volt rails at similar power levels. PV transformers are very sturdy and reliable.

Other than that, ANY SS amp with similar voltage rails can provide its powr tranny. I just happen to be most familiar with the PV line.

[acorkos]

thanks enzo....what about the power transformer (part number 027668) that fender uses in the deluxe 90, deluxe 112, princeton 112 and princeton 65 DSP? it looks to put out about 30vac on the secondaries....does it run at the correct current range?

[Mark Black]

Here's another thought -

On lots of power transformers there is an embedded thermal fuse in the windings. Sometimes these can blow open from a power surge. They are usually in series with the primary windings, and often make use of an extra lug which appears unused but which is actually the point at which the fuse connects to the windings. The other end of the fuse gets connected to power in.

I notice an extra lug on the top left of your picture with what looks like a very thin insulated wire attached - it would be my guess that this may be one attachment for a thermal fuse. Does that lug get a wire attached to it when installed? If not that might be the actual winding connection, fed through the fuse.

Based on the logic that lots of transformers were built without these safety devices and instead relied on the line fuse I have successfully bypassed these open thermal fuses in the past when replacements were expensive or rare. In at least one case (my yard light tranny - not rare) I was able to dissect/remove/replace the thermal fuse with a correct value. Just wanted to see if I could...

If you DO find & bypass one of these I would suggest firing the thing up through a lightbulb current-limiter, just in case the primary windings are actually shorted. I would also monitor the tranny for excessive heat for a while in case the thermal fuse blew for its intended reason instead of a surge.

Good luck!

Mark

[acorkos]

I notice an extra lug on the top left of your picture with what looks like a very thin insulated wire attached - it would be my guess that this may be one attachment for a thermal fuse. Does that lug get a wire attached to it when installed? If not that might be the actual winding connection, fed through the fuse.

top left lug in the pic connects to the primary live wire

[Mark Black]

top left lug in the pic connects to the primary live wire

Does the other primary connect at bottom right lug? Looks like the solder is disturbed there...

If so the top left might go through one of those fuses to the "0" connections on the bottom.

Easy test - check continuity between the normal places the primary wires connect (probably shows open I'm guessing), then check continuity between either of the "0" lugs and either of the "120" lugs. If you now have continuity it might mean all you have to do is move the wire that used to connect at the top left to one of the "0" lugs, thereby bypassing the fuse.

Hope this helps -

Mark

[Mark Black]

I just saw your picture on my nice bright monitor here at work and it looks like the top left terminal is labeled "TF". If that doesn't stand for "thermal fuse" I will be very surprised.

[Enzo]

I think Mark is right, I thought about thermal fuse and then didn't mention it. In teh face of that "TF" it is even more likely.

At this point you are at the "what is there to lose " point. Carefully slice open the paper wrapping from the TF lug down to the lower left lug. See if there is not a component that looks like a diode. Usually they are bright shiny metal and the leads are also shiny. If there is a number on it like 130, that is the temperature. You can jump across it for testing to see if it works otherwise, adn to see if the amp works otherwise. SOMETHING blew the thermal fuse. You can get thermal fuses at Mouser, MCM, and other parts houses.

If there is continuity through the windings between the 0 and 120 volt lugs, but no continuity up to the TF lug, that tells the tale.

[acorkos]

thanks for your replies. i sliced and diced through paper, cardboard and plastic, but i couldn't find any diode or fuse...it must be tucked deeper into the bobbin than i can get to or even see. anyway, i bypassed the 'TF' lug and connected the live AC wire directly to the '0' lug....i get erratic voltage measurements on one of the 30V lugs and 0 voltage on the other.

[Mark Black]

How about between the two 30V lugs?

And/or between the secondary "0" and either of the 30V? (or is that how you were measuring...)

Oh - and that was one of the bottom "0" lugs to which you connected the line wire right?

[Enzo]

Oh well, worth a shot.