repair or replace rx500b

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rx500b
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repair or replace rx500b

Post by rx500b » Wed Oct 11, 2006 11:52 pm

Hi,
The RX500B which I purchased in 1985 has recently lost the sound on the right channel. Left channel works fine, as well as all buttons and displays. I am curious what the likely cause of the right channel going out might be and if it is worth having it repaired or if I should just throw this one away and buy a new one. Perhaps Andy has seen enough RX500's to be able to comment on what usually fails on these units. This one lasted for 20 years without any problems whatsoever, and it still looks new.


The unit does produce nice quality sound when working properly, and it did cost me around $500 US when I bought it, which was about 1 month's rent at the time.

Thanks from California.

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andywilks
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Post by andywilks » Sat Oct 14, 2006 11:19 am

Lucky you found us. I have worked on a couple of these beasts from ~1984?

The common problems stem from the small vertical board 3"x2" just in front of the aluminium heat sinks. Many of the small transistors run very hot and you'll find the board rather sunburnt too! As a result of many yrs of hot/cold, you get a lot of minute fractures in the solder joints. You need to unsolder the board from the main board, then painstakingly resolder every joint. With age you'll also find some component legs oxidised and not too happy to take solder. Not a DIY job- unless you are good at soldering. There can also be fractured joints on the main amp board.

Be careful if checking with the power on as there are both +65 and -65v supplies so there are some transistors with both ie 130volts across them!

Its unlikely the main amp channel components have a problem as that would cause the protection circuitry to cut the relay out (both channels)
It is also possible you may have an input switching fault.

I have a paper manual for the RX500 and could scan/email diagrams if you need them.

This was the top model 120 watt amplifier etc in its day so is packed with wires, boards etc and not that easy to work on. Its also likely that many service departments won't have seen anything this specialised either, so be careful letting a tv technician have a dabble!

Hope that helps.
Good luck
Andrew

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Andy Cippico
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Post by Andy Cippico » Thu Oct 19, 2006 8:02 pm

I'm impressed, Mr. Wilks! Do you know your stuff, or what?

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andywilks
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Post by andywilks » Fri Oct 20, 2006 8:45 am

Just had another thought. Could also be the speaker output/protection relay with an oxidised contact. it is possible to remove its lid and clean the contacts.

Mr Cippico, why thank you.
We are the longest standing JVC account going back to 1970, so know everything about JVC.....
besides, I've been chained to my bench 168 hrs a week for years now....need to get out more... :roll:

rx500b
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RE: "Many of the small transistors run very hot"

Post by rx500b » Wed Dec 26, 2007 5:46 pm

Thank you very much for the information. I was a bit thrown off at first because the vertical boards on my model do not have transistors on them, so the first time I tried to fix this back in Oct 06 I stopped because of that. Over the Christmas holidays this year with some time on my hands, I decided to either fix it or throw it out. I found 2 horizontal boards, one 3"x2" and one 5"x4" and the solder joints look like new. The 5"x4" has 2 power transistors on it. Looking on the solder side of the board, there was some brown resin/substance between the gate and the source which could have possibly shorted it out. Scraping this off and swabbing with isopropyl alcohol removed most of it.

There was also some dark brown substance which had leaked out of the big capacitors and the smaller large capacitors. I removed some of this which was on a couple of resistors and put the boards back in.

Works great now. It is a great pleasure to listen to this receiver.
:D

The summer of 2006 (when this problem occured) I was living in a very hot house and the summer was very hot. I remember turning it on during a hot day and smelling some odors. Perhaps it got too hot that day. I think that is when the problem occurred. I hope the leaky capacitors do not cause future problems. It appears to sound perfectly normal to me now. With only this problem during the 24 years I have owned it, I must say that I am impressed with the JVC brand now. I can also say that the original JVC dry cell batteries which power the memory when the unit is turned off are still showing no signs of leaking. After being turned off for over 1 year, the memory was still intact also. I was going to replace them but it says do not replace with Alkalyn batteries, so I am keeping the original ones in the unit.

Thanks so much for pointing me in the right direction and for taking the time to respond to my inquiry! You really know your stuff !

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Post by andywilks » Sat Dec 29, 2007 10:49 am

Great to hear its sorted.

I would be surprised if there were leaky capacitors. As mentioned before its the (brown) glue they stick them to the board with that can become slightly conductive with age.

Sorry to have thrown you with not having a vertical board... this was the similar RX9, I now remember.

regards
Andrew :D

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Post by chris » Fri Jan 11, 2008 8:27 pm

Hi...I found Andy's forum while looking for info on JVC's R-X500. My dad passed away 2 years ago and I inherited his system which included this very fine receiver. He lived in Nashville, TN and had been sick for a long time...In short, the receiver was not used for quite some time before his death. I brought it home to Montana and it was stored in my basement for a year and 1/2. Last month, my son and I brought it upstairs and had a skilled friend blow the dust out of it and clean it up. When we lit it up we had the same experience. It clicked and displayed very dimly, if at all. My friend suggested that I let it sit, turned on, for a time...(Oh yes, I nearly forgot. I did change the batterys in the back). After approx. 30 minutes...the receiver lit and has been working good as new for some time. I wondered if there wasn't some kind of boot up the primitive computer needed to go through...never the less...it works great! Hope this helps.

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Post by andywilks » Sat Jan 12, 2008 2:39 pm

Hi

Good news yours is still working

The electrolytic capacitors can if, left to sit for months/years, not smooth as good as they did, so leaving powered up will often bring them back from the brink.

The moral is don't leave electrical gear unpowered for too long especially when old.

As for booting up... these aren't Windows you know :wink:

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Post by bobrob » Fri Jul 11, 2008 5:59 am

Greetings. Similar to Chris, I found this forum while Googling for the R-X500. I got mine used in 1986, and it's been generally a great piece of gear. Something that started happening a few years ago, though, is that once every now and then there will be a sudden pop out of the right speaker for no apparent reason. Any ideas as to what might be causing this and how to rectify it?

Thanks!

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Post by andywilks » Fri Jul 11, 2008 10:10 am

Hi The most likely cause is a dry/fractured solder joint. If you tap the unit, can you make it happen? If not that then it will be tough to diagnose where the pop comes from.

Get the units soldering, especially on the main amp and power boards checked for problem solder joints.

Andrew

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Post by bobrob » Fri Jul 11, 2008 10:40 pm

Hi Andy!

No, I can't reproduce it by tapping on it (or by anything else for that matter). There's no pattern at all to it, but the pops occur at what seems to be a consistent amplitude (loud), regardless of the volume. I was thinking it could maybe be a random discharge from a marginal cap somewhere in the pre-/power amp chain, though that's pure speculation.

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Post by andywilks » Sat Jul 12, 2008 1:52 pm

Doubtful its a cap really.

if it does it with the volume down its in the main amp. Is it on both channels..if so then its power supply.
When it does it does the amp cut out?

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Post by bobrob » Sat Jul 12, 2008 7:13 pm

It only affects the right channel, and has never tripped the protection. It's a consistently loud pop regardless of the volume setting, though, naturally, it's masked somewhat when audio is played at higher volumes.

I'm trying to recall if I've ever heard it through headphones. If I did, it seems that it was only perceptible as a click.

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Post by andywilks » Mon Jul 14, 2008 12:04 pm

OK that narrows it down a fair bit.

I would bet on poor soldering on the pins of a small transistor on that channel. I would advise against trying to find it yourself unless you are fairly confident with a soldering iron, in case you leave a short etc.

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Post by bobrob » Wed Jul 16, 2008 6:18 pm

Although my soldering skills are pretty solid, I would think that if it was in fact a loose solder joint, the pop could be reproduced more-or-less at will by tapping the unit as you'd earlier suggested.

Unless I'm misunderstanding your meaning, it's looking like I'm resigned to living with this sporadic anomaly, since it wouldn't be worth the cost of having a repair shop even look at it let alone repair it, if such a facility could even be found that would be able to fix this 30-year old receiver.

Thanks for your help, Andy!

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