Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Thread Tools Search this Thread
Old 13th April 2005, 06:52 PM   #1
pjeaton is offline pjeaton  United Kingdom
diyAudio Member
Join Date: Apr 2005
Location: London, UK
Unhappy Tech advice needed for Rotel RB-850

Hello All,

My Rotel RB-850 amp has an annoying problem.

Either of the two sound channels keep switching themselves off during operation, after, say 30 monutes of operation. Sometimes the channel will come back on again after a couple of minutes. They've never gone off at the same time.

Giving the case a whack with my hand doesn't seem to help, but if you power it off and a fraction of a second later power it back on again, both channels come back on again.

Can anyone give me an idea as to what might be wrong?

Does anyone have any circuit diagrams for this amp?

I have a degree in electronics, but I got that 15 years ago and have never really done anything since then with analogue stuff. (I'm pretty good at fixing old computer circuit boards though :-) )

I really like this amp and have owned it from new since the late 80s so I'm pretty happy to get stuck with the soldering iron.

Any thoughts very much appreciated!

Phillip Eaton
London, UK
  Reply With Quote
Old 13th April 2005, 07:18 PM   #2
Netlist is offline Netlist  Belgium
diyAudio Moderator Emeritus
Netlist's Avatar
Join Date: Jan 2003
Hi Phillip and a warm welcome.

Does the amp have an output relay? Does it turn on when the amp switches off?
Probably not as most amps have one relay for both channels but let me ask just in case this one has two of them.
What DC do you measure at the output? Did you check for bad solder joints? Are your interconnects OK?

  Reply With Quote
Old 13th April 2005, 07:21 PM   #3
tubenut is offline tubenut  South Africa
diyAudio Member
tubenut's Avatar
Join Date: Nov 2002
Location: South Africa, Jhb
If there is an output relay the contact could be dirty/worn....
  Reply With Quote
Old 14th April 2005, 01:31 AM   #4
anatech is offline anatech  Canada
diyAudio Moderator
anatech's Avatar
Join Date: Jun 2004
Location: Georgetown, On
Hi Phillip,
Take the cover off and locate the relay. Give it a "twack" with your finger. Try from different angles with the volume low. Also, slowly operation the various switches. The tape loops are good for this type of thing.
  Reply With Quote
Old 14th April 2005, 05:19 PM   #5
diyAudio Member
mpopovics's Avatar
Join Date: Apr 2002
Location: Hungary
Default Rb850

There is no output relay in RB850
Check the electrolytics, this is an older power amp, and could bethe root cause, that they are just simply dry out.
My brother's RA-8xx-series integrated had same problem.
Attached Images
File Type: jpg rb850_1.jpg (97.2 KB, 300 views)
  Reply With Quote
Old 14th April 2005, 09:27 PM   #6
anatech is offline anatech  Canada
diyAudio Moderator
anatech's Avatar
Join Date: Jun 2004
Location: Georgetown, On
Right you are, no relay on this. I have seen some with bad solder connections to the speaker terminals. Of course you may have bad connections anywhere that don't always react to a sideways slap to the case.

  Reply With Quote
Old 14th April 2005, 09:55 PM   #7
Join Date: Mar 2005
Location: Australia
could be the overload protection shutting down the channel
sensing some kind of fault
  Reply With Quote
Old 14th April 2005, 11:22 PM   #8
anatech is offline anatech  Canada
diyAudio Moderator
anatech's Avatar
Join Date: Jun 2004
Location: Georgetown, On
I think what we need now is a schematic.
  Reply With Quote
Old 12th September 2006, 05:30 PM   #9
gni is offline gni  United States
diyAudio Member
gni's Avatar
Join Date: Sep 2006
Default Rotel RB850 Shut Down Problem

I have been researching the Rotel RB850 amplifier for several years.

No relays in this model.

Maybe a transistor on the heat sink is overheating since it
might have come loose. .check the mounting screws on
the heat sink (while the power is off). Also, take the cover off
while operating and put your fingers near similar transistors on
both sides. . .there should be equal heat coming off of them.
This could account for the left channel cutting out at different
times than the right channel.

A bad capacitor is the next suspect. . . the transistors
could be shutting down since there isn't enough voltage to keep
them open. Take the time and replace the electrolytic caps.
There are better caps out there. . .re-solder all contact points.
Tthis could take an hour or two but on older amps. . .worth the time.

The Rotel RA-02 has a similar schematic. . .a few extra
parts and some missing in other areas. . .This site offers
for free schematics of some similar amps to the RB850.

I will answer any questions you may have (as far as I know).


Chris Browne
Ground Noise Industries
  Reply With Quote
Old 12th September 2006, 06:03 PM   #10
AKN is offline AKN  Sweden
No snake oil
diyAudio Member
AKN's Avatar
Join Date: Aug 2005
Location: In the middle of Sweden
Send a message via MSN to AKN
Hi There!

Check bridge mode switch also.

Only have schematic on one amp section.
Attached Images
File Type: jpg rb850.jpg (86.8 KB, 197 views)
/ Anders
  Reply With Quote


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Low tech speaker switch needed clippo Multi-Way 4 30th April 2009 02:43 AM
Rotel RCD971 reading problem - assistance/advice needed fixilator Digital Source 5 13th September 2008 10:32 AM
Tech help needed Threshold S/300 MkII optical bias georgehifi Pass Labs 4 18th January 2005 06:49 PM
Tech help needed Threshold S/300 MkII optical bias georgehifi Solid State 15 17th January 2005 01:30 AM
Speaker Tech needed in Los Angeles area dmfraser Multi-Way 2 3rd November 2004 11:18 PM

New To Site? Need Help?

All times are GMT. The time now is 11:48 AM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2