Axiom Home Page Forums General Discussion Technical Questions My Rotel RB-1080 lest channel died

I've had this amp for about 12 years now. Never a problem. Noticed yesterday the left speaker was silent. It's definitely the amp, and not the speaker or pre-amp output.

Thought I might tear the sucker open and look around a bit. Hoping something obvious jumps out at me. I'm not an electronics tech, but I can follow a logic drawing, use a Fluke, and solder.

Any tips, or suggestions before I start the autopsy? My options for electronics repair are quite limited. Shipping costs would be as much as buying a refurbished unit, I suspect..

Hi Michael,

The first thing to do is to remove the top panel and inspect the two fuses on the main amp board of the channel that is not working. You will probably find that one or both of these fuses are bad. Unfortunately when the 1080 starts blowing fuses it is usually an indication of other issues that will cause the fuses to blow again in time. That would probably require a trip to a service depot, unless you are handy with a soldering iron?

Thanks,

Andrew

Thanks Andrew! I am pretty handy with an iron, if I know what to replace. I'll open up the case and look for fuses. I have nothing to lose at this point.

Sometimes the real problem is acquiring the needed parts. Failing any blown fuses look for caps that are leaking or bulged and use you nose, sniff around for anything that smells like melted plastic. Take some pics and upload them if you cant see anything. When I fixed my plasma the culprit was hiding under a heatsink but I sniffed er out bye.

Oh no, say it isn't so. A bunch of us got them about the same time.

I will post up what I find. It just stopped working Rick. Mellow, background music. I haven't been cranking the tunes for months, maybe that's why? She's mad at me....

Any news Mike?

Not yet, no... Taking advantage of an unusual stretch of sunny days here. I just bypassed the 1080 and am using the Denon 3808 for double duty now.

It is a fuse... I can't find anything that looks like it got hot. No burnt smell anywhere. I need to find a fuse now. Fuse holder is to the left and above of where it is standing on end.

What's that gold plate in the middle?

Some kind of junction for the four round things under it, I reckon. I haven't a clue what 98% of the stuff inside this thing is..... Sure is built stout though. Nothing flimsy or cheap in this sucker.

the round things are large capacitors, and the plate on top seems to be connectors (+ -)

Is it back in service Mike?

You are forgetting to add the Rotel to your Rotel... That will fix everything.



I would stay away from the HOT one though as it can cause overheating.

Silly me. I didn't see the caps underneath the plate.

Need to find a fuse. Work and all keeps interfering with my business hours shopping....

I think you can buy them online.

Here are some "high end" fuses. Supposed to make a difference.

Not in a million years will I believe that a fuse will improve the sound of your system, but hey, some people sware by them.

www.element-acoustics.ca/products.php?cid=7&sid=25

Michael, can you take a close-up of one of those blue capacitors (the big cylinders) on the amp board? In your second photo it looks like there is some black stuff where it meets the PCB. Rotel, or more likely their 3rd party manufacturer, used a corrosive glue under these capacitors which will leech out over time and start to damage the parts around them. The blown fuse might suggest that some corrective action is required.

That gold plate is likely a piece of plated copper. It is the central "star" ground point for the amplifier, and all ground returns (transformer centre-tap, safety earth, main power supply capacitors, amplifier PCB, input stage PCB, speaker negatives) will all connect to this bus plate.

Indeed. It must be nice not to have to worry about fast transients, surges and ring waves on I/O in audio. Then you can get away with a pseudo star ground.

As an audiophile, I take this as Rotel cutting corners and removing the musicality of ring waves.

Thanks for looking Andrew. Here are a few more pics. All the blue capacitors appear to have some black substance around the base. Not sure if I'd say it was leaching though. More like, just glue??

On that first new photo, the black goop is right ontop of the resister to it's right. I would make sure it's not about to take that out.

I don't see any bulging on those caps. Looks like silicone rubber to me for shock and vibration withstand.

Yes, Ken. Ring waves are indeed very musical. If you were connected to a ring wave generator, the Violent Femmes could use you as the protagonist on this Oedipal tune.

https://youtu.be/BUI5GlvEk7Y?t=3m3s

Wierd with all that heatsinking all the way around there appears to be only one output transistor per channel. The guts of that rotel are a thing to behold!! Real parts instead of icbs. The guts of the arcam integrated I sold looked like a computer video card.... I love tanky electronics.

So after looking at the capacitor above the blown fuse a bit closer, and comparing it to the other three, it looks and feels like it's bulged. I can also wiggle it a bit, and the others are firm.

I did find some fuses, but I suspect that if I hook this thing up and test it, the fuse will probably just blow again.

How are these things attached to the board? I'm hesitant to start pulling on it.

if the three are the same, and one of them has gone, then I would tend to look into replacing all of them at the same time. Nothing worse than fixing something to have it fail in 3-6 months with the same problem.

I agree (also replaced all four fuses).... Need to figure out how to perform that repair though.

You will need to remove the circuit boards from the unit to get to the back of them. You'll need a solder sucker and some wicking wire and remove the solder from the two leads on the back. you might need to wick with the wire to get the solder that is on the front side too.

https://www.youtube.com/watch?v=YCSNWi3UHf4

Now with this board you have the second hard part in they also glued them on. So you need to see about how to get the glue off as well. I'd wait to see if Andrew has some great methods as that is likely something that he has done many more times than I.

Thank you! After watching the video, the cap that I thought was bulged, looks identical to the one that the guy used as an example of a blown cap.

OK, one more question.... Where does a person buy capacitors? And are they only made in China?

Best bet is to remove it and get all info off the capacitor and determine its rating and if it is bipolar . Digikey is a great place to find matching capacitors. Capacitors with similar specs may not be physically the same size as yours so I would try to match at digikey

Richard

Thank Richard. I was able to get all the data off the little bugger without removing it. It'll take some work to get the board out and separated from the heat sink. I figured I'd just wait till I get the replacement caps, and my "solder sucker" on hand. I'm heading down uncharted territories here..... Kinda fun really. My solder 'sucker' is on order.. LOL...."sucker". What a name.

Nichicon
VX(M)
100V
1000UF
HO 206
85C

I measured it too.... .795"(20.19mm) X 1.415" (35.6mm)

I tried to find it on Nichicon's web site, but it does not look like they make this one anymore, and there are no VX series (general purpose).

Full VX description:
ALUMINUM ELECTROLYTIC CAPACITOR
Axial Lead Type
Compliant to the RoHS directive (2011/65/EU)

http://www.nichicon.co.jp/english/products/alm_mini/index.html

I'll see what Digikey has.

I'm wondering though, if I'm going through all this trouble to replace these buggers, is there a better type than "general purpose"??

There is lots of discussion about the effects of capacitors and their quality/materials and whether or not its audible as it pertains to crossovers. I used Axon capacitors from Solen and honestly if there is a difference I'm to deaf to hear it. I put my home made speakers up against my M2's and could hear no difference. You could go better quality for the benefit of longer life but not sure how you could prove it. The so called better quality caps are typically quite a bit larger from my experience.

BTW when using the solder sucker you need to be quick. A good iron is important and the second you see the solder melt shove the sucker in there ,don't worry about touching the solder iron on the way in.

I ended up calling Digikey and talking to a tech guy. They were able to cross reference the cap I have with a different cap they had in stock. Slightly different, same manufacture. Nichicon UFW2A102MHD

http://www.digikey.com/product-search/en?keywords=5%20493-3185-ND

The tech suggested I use a hot-glue gun, and that's what he uses. Just make sure I don't use a corrosive or conductive glue.

Finally got around to finishing this little project.

IT LIVES!! No guaranty how long it'll live, but it sounds just like it did before....

The capacitors I got in from Digikey are slightly larger. The little wires are closer together too, so I ended up bending them outward a bit to get them through the holes in the board.

The solder sucker thing worked just fine. Took several attempts to suck all the old solder out is all.

Here's a couple tips for anyone who may find themselves needing the do this little 'repair'.

The hardest thing to do, is to separate the board from the heat sink. It would have been simple if I could have just disconnected all the wires, but some are soldered, and some of the little connectors did not want to cooperate, so I didn't force them and just left all the wires connected.

Board with new caps installed. To separate from the heat sink, there are all the little black whatchamacallits and four small cap screws that attach the board directly. The whatchamacallits kinda stick after the screws are removed, so I ended up using needle nosed pliers, to give them a gentle twist to break the bond. After all the screws are out, I then just folded the board away from the heat sink, carefully.


Back of board after separated from the heat sink.


The two small dots of solder are the new cap pins, soldered in place. They are the C624 pins. The caps came with wires about 1 inch in length. Glad I bought an extra cap, cause I cut the wires too short on the first one. For the remaining caps, I left them uncut, inserted them through the board, applied a good sized dollop of hot glue, ran them home and let the glue set. Then I cut the wires and soldered them.


If anyone has questions or needs clarification, let me know. I'll do my best to answer.

Nice! A working amp and the pride of having fixed it yourself!

Glad to hear old faithful is working again.Good work Mike

Those are some nicely soldered joints!

I do feel sorta good about fixing the old gal. I love the amp, and didn't really have anything to loose. Plus, I learned a few new things. Win-win... I think I'll stick to wrenches and power tools though.