Rotel RA-920AX - Page 2 - diyAudio
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
Reply
 
Thread Tools Search this Thread
Old 30th June 2010, 11:52 PM   #11
tooch is offline tooch  Australia
diyAudio Member
 
Join Date: Jun 2010
Quote:
Originally Posted by gunter75 View Post
I have the same amp (also given it along with a RDC-975 which I have already fixed the draw on) and the same issues with the DC. So far I have replaced 8 of the caps and noticed a little change but for me the mV are still around 95 & 70. I will be replace the remainder soon when they arrive along with the differential pairs. Hopefully all goes well, but I would also be very interested in fixing the grounding.

interested to see how well you get on tooch, this amp seams like it is worth the effort. I have had a listen to mine and was very pleased and that was before I stared repair
I'm going to price up all of the caps today and also do a quick check of the resistors, to see if I should replace all of them at the same time.

I think it's worth the effort too!

Quote:
Originally Posted by jaycee View Post
Looks identical to the circuit of my RA-930AX. I'd be wondering why the bridge rectifier fried.

It might be worth checking the regulators for the opamps, and the opamps themselves - it's possible that the faulty bridge rec has caused some damage.
I desoldered the 776's and 896's and gave them a quick check with the diode check on my DMM, all appeared ok. Is there a more conclusive test I can do on them?

Quote:
Originally Posted by abraxalito View Post
OK then that's a deal Your side of the bargain is to report back on how it changes the sound!


I'll need a little time to print out the layout and schematic from the kindly provided service manual, annotate them and scan them back in. Or perhaps I could find a way to do it electronically. Stay tuned!
Excellent, looking forward to it

I'll try and get the amp sorted to a 'baseline' level first, so I can see how it's meant to sound stock. Then I'll do the mods and report back!
  Reply With Quote
Old 1st July 2010, 07:59 AM   #12
diyAudio Member
 
east electronics's Avatar
 
Join Date: Jan 2006
Location: Athens GREECE
Quote:
Originally Posted by jaycee View Post
Looks identical to the circuit of my RA-930AX. I'd be wondering why the bridge rectifier fried.

It might be worth checking the regulators for the opamps, and the opamps themselves - it's possible that the faulty bridge rec has caused some damage.
rotel has a history of blowing rectifiers on many models but most of times you just replace them and go
__________________
SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
  Reply With Quote
Old 3rd July 2010, 03:13 PM   #13
jaycee is offline jaycee  United Kingdom
diyAudio Member
 
Join Date: Apr 2004
Location: Norwich, UK
Quote:
Originally Posted by sakis View Post
rotel has a history of blowing rectifiers on many models but most of times you just replace them and go
Why do they blow though, admittedly I thought the one in my RA-930AX looked a bit weedy... I did think about putting a 16A one in mine instead of the 4A inline one that was in it. Then again, its only 30W/ch into 8 ohms.
  Reply With Quote
Old 3rd July 2010, 03:32 PM   #14
diyAudio Member
 
east electronics's Avatar
 
Join Date: Jan 2006
Location: Athens GREECE
well its rather obvious Jaycee ... rotel is a decent constructor ...machines they've made of that series and other similar play way above average or lets say from the same range of other or similar products

they do have proper trafos and they do have enough capacitance for their circuits ,often also one trafo but two power supplies

while they have bearly enough ...or almost enough rectifiers and no soft start circuit ...so that will complete the picture for you ..... one power off and one power on that could be also be a loose plug/socket or a mains instand power loss and there it goes ....

i had replaced many in the past ... the point is that in other manufacturer either the trafo is too small to provide enough to blow the rectifier or caps to be charged are also not a heavy load to the rectifier since these are small in capacitance anyway ...

kind regards sakis
__________________
SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr

Last edited by east electronics; 3rd July 2010 at 03:38 PM.
  Reply With Quote
Old 4th July 2010, 07:20 AM   #15
tooch is offline tooch  Australia
diyAudio Member
 
Join Date: Jun 2010
Yeah as Sakis said they just seem very under-rated for the job at hand. When I power up my 920 you can feel and hear the transformer 'sucking' the power, so no surprise the little 2A rectifiers blow!
  Reply With Quote
Old 5th July 2010, 03:10 AM   #16
tooch is offline tooch  Australia
diyAudio Member
 
Join Date: Jun 2010
Ok, replaced all the capacitors- I think the amp sounds better, but the DC offset is still there, 88-90mv.

Where to next?!
  Reply With Quote
Old 5th July 2010, 05:19 AM   #17
diyAudio Member
 
bobodioulasso's Avatar
 
Join Date: May 2008
Adjusting R607 /608?
  Reply With Quote
Old 5th July 2010, 06:04 AM   #18
diyAudio Member
 
east electronics's Avatar
 
Join Date: Jan 2006
Location: Athens GREECE
adjusting ???means exactly what ??? these are probably fixed resistors what to adjust???

you probably mena to replace with something else that will give other type of ofset ...or replace them with a trimmer ..that could be a more realistic option

best thing will be to first verify all voltage arround there to se what is going on .... there might be a chance of something else also .... for example whta is your normal voltage down there ??? or down under ??? 220 or 240 ???

it could be that the amp is setup for 220 this lilte extra voltage might or could bring the amp outof balance ...so verify voltage before everything else ...also from the schematic to the testing points on the pcb ...

then verify close to ltp resistors for drifting .... if any suspect replace them all with metal film 1% ...that is also some type of upgrade


one other thing iwould like to do and since pcb and parts location helps is to join the ltp tranisotrs for thermal junction ...that also might solve the problem


regards sakis
__________________
SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
  Reply With Quote
Old 5th July 2010, 06:38 AM   #19
diyAudio Member
 
bobodioulasso's Avatar
 
Join Date: May 2008
You seem to like question marks very much...
  Reply With Quote
Old 5th July 2010, 07:04 AM   #20
diyAudio Member
 
east electronics's Avatar
 
Join Date: Jan 2006
Location: Athens GREECE
well ... not really .... i have other thinks that i like also ... only trouble is that i have a broken keyboard
__________________
SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
  Reply With Quote

Reply


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
Rotel Ra-931 argonrepublic Solid State 3 23rd June 2009 06:43 AM
rotel ra 820 diymax62 Solid State 1 11th May 2009 12:05 PM
Rotel RA 931 argonrepublic Chip Amps 0 20th April 2009 01:26 AM
schematics of Rotel RA-971mk11 / RA-971 digitaldiablo Solid State 0 12th June 2003 04:03 PM
Rotel RA-820B jean-paul Solid State 0 9th December 2002 08:00 AM


New To Site? Need Help?

All times are GMT. The time now is 10:02 PM.


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