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Rotel power amps electrolytics question

quietmole

quietmole

Wholly member
Hi all,
I seem to be having a fun time with eloctolytics these days!

Does anyone know if Rotel glue in their big power supply caps to the pcb, as I have seen suggested elsewhere, or am I on a bit of a streak of leaky ones?

Any help very welcome.

Cheers

Geoff
 
The old 820/840 series certainly had glue on the large caps, which ends up looking a lot like leaky discharge as the years progress.

IMG_20181226_101837.jpg


IMG_20181226_101935-e1545827968367.jpg
 
Craig B said:
The old 820/840 series certainly had glue on the large caps, which ends up looking a lot like leaky discharge as the years progress.
Click to expand...

No that looks just like the stuff I'm talking about! It's just not what you'd expect inside a professionally assembled unit is it?

So I'm now wondering if I've misjudged my 850 power amp's failure and it might well be something other than the big caps...

Hmmm....




https://i.postimg.cc/Qxk3ghDq/IMG-20220327-125746.jpg
 
quietmole said:
No that looks just like the stuff I'm talking about! It's just not what you'd expect inside a professionally assembled unit is it?

So I'm now wondering if I've misjudged my 850 power amp's failure and it might well be something other than the big caps...

Hmmm....




https://i.postimg.cc/Qxk3ghDq/IMG-20220327-125746.jpg
Click to expand...
Generally, these all look nice and hot melt glue like before the ravages of time and temp take their toll and cause all to petrify.

Having said that, your's may well have been a Friday afternoon leading into a banker's holiday weekend job, and/or from a mad rush production batch following a glowing What Hi-Fi awards/review issue.

What symptoms of failure are we talking about here?
 
You need to clean that glue off. It tends to corrode any component legs it touches and causes havoc. I regularly have to deal with this is Marantz and CD players and usually end up having to replace a bunch of wire links and components that had glue on them.
 
Craig B said:
Generally, these all look nice and hot melt glue like before the ravages of time and temp take their toll and cause all to petrify.

Having said that, your's may well have been a Friday afternoon leading into a banker's holiday weekend job, and/or from a mad rush production batch following a glowing What Hi-Fi awards/review issue.

What symptoms of failure are we talking about here?
Click to expand...

Ah those Friday afternoon jobs in the 80's, after a liquid lunch...

Got a very small signal coming through, but largely no amplification - fuses okay though.
 
Mike P said:
You need to clean that glue off. It tends to corrode any component legs it touches and causes havoc. I regularly have to deal with this is Marantz and CD players and usually end up having to replace a bunch of wire links and components that had glue on them.
Click to expand...
Trouble is Mike, it's been on there for donkey's, so is well and truly 'bedded' in!
 
quietmole said:
Trouble is Mike, it's been on there for donkey's, so is well and truly 'bedded' in!
Click to expand...
Yup, it's a bugger to shift but needs to be done. I get the worst off by chiseling it off with a blade or old screwdriver then clean further with IPA and cotton buds.
 
I was reading earlier that someone uses chopsticks sharpened with a Stanley knife to clean off old glue. It doesn't damage the board like metal can, and obviously you can easily keep resharpening them.
 
Fatmarley said:
I was reading earlier that someone uses chopsticks sharpened with a Stanley knife to clean off old glue. It doesn't damage the board like metal can, and obviously you can easily keep resharpening them.
Click to expand...
Good idea. I sometimes use a sharpened ice-lolly stick.
 
bugbear said:
Very disappointed by this thread.

I was watching that amp on eBay ;)!

BugBear
Click to expand...
Well I revised my narrative after the input of wiser heads than my own, so the listing was withdrawn as it was potentially misleading. I didn't want someone changing out the big caps and then moaning away at me that it hadn't sorted the problem (that sort of thing does happen, sadly). I have put that one back on the bench for a closer look.
 
quietmole said:
Got a very small signal coming through, but largely no amplification - fuses okay though.
Click to expand...
Sorry, I just remembered that it was I who asked what the symptoms were before we got off topic with scraping tools and such.

I'm no amplifier circuit diagnostician for sure, but I have found that it helps those in the know on here to advise further if some basic test results are provided. For a start, one can provide such info as heat sink temp either channel and a reading of DC output levels at the speaker terminals. Just let the amp idle with nowt plugged in and have a feel of the heat sinks, as well set your meter to DC and probe each pair of speaker sockets.

For example, I've a pair of Linn LK275 amps here, each with a stone cold heat sink on one channel and showing large DC voltage on the same side. Paul R of this parish suggested that "having DC and no warmth might suggest that the output devices are failed, one short, one open. No current flowing so no heat". Contrast this with the local Linn dealer who, sight unseen, suggested a recap, and that they send these out to some local PA service shop for such. The dealership used to do all Linn and Naim servicing in house, this back before they became an A/V 'boutique' to the gentry.
 
Hi Craig,
No worries, the scraping stuff was all useful input too!
Thanks for your comments. I've a sneaking suspicion I may have been premature in consigning the amp to the spares department. I was confident when I first made the judgement, but I have to confess to failed due diligence in not repeating all diagnostics with progressive swap-outs. I don't want to tempt fate, but I have a feeling the old girl can still sing.

That description of the change in dealership focus is so true. Back in the day you could have a conversation with someone who knew what you were talking about and loved the kit. Now it's just margins. Only a few enthusiasts left at the dealer end.

I'll have a daylight look over the 850 this weekend and see what turns up.

Cheers
Geoff
 
Hi Craig,

You'll possibly be pleased (though only half as much as I am) to learn that I've had the amp doing its thing all weekend from streamed/vinyl/cd and AV sources and it's been fine. Wtf I did originally to damn it so casually I have no idea. Early onset something or other. But the bottom line is that Lazarus is up and about and truckin' which is good news in these parts.

Cheers and best regards,
Geoff
 
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