Need advice on replacing caps in amp P/S - 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 17th April 2003, 04:19 PM   #11
diyAudio Member
 
cdwitmer's Avatar
 
Join Date: Apr 2003
Location: Tokyo
Default You guys are great!

Wow, I am really blown away by how kind and helpful you gentlemen are!

I just got back from a concert and despite the fact that the music was absolutely heavenly, I have a splitting headache so I'm not going to answer each of you separately, sorry.

Jonathan, I'm almost certain we've met before. I think we met at a demonstration of a truly awesome analog turntable quite a few years back. If I recall correctly you were living in Suginami Ward and had some sort of a business connected with Scandinavia -- I think the name had "Scan" in it. I was, and still am, living in Tachikawa, albeit with many more kids and much less hair.

Passfan, you would be correct in assuming I don't really know what I'm doing! I'm groping around in the dark. I didn't test these caps; the sound in one channel rapidly degraded -- just a fall-off in volume and general "dirtiness" to the sound -- and all the components in that channel are "tepid" whilst the other (good-sounding) channel gets good and hot. So I said to myself, "After nearly 30 years the capacitors in this amp can't have much life left in them; I'll just replace them all and see if that solves the problem. And if it doesn't I'll send it out to a professional for repairs."

I have a multimeter but using it around such massive caps scares me a bit. Maybe that's just being silly . . .

I'm going to post more of the schematic now. The right-hand half goes in this post, and the left-hand half in the next.

Many thanks to you all! Truly a heart-warming group.
Attached Images
File Type: jpg m955rght.jpg (32.9 KB, 309 views)
  Reply With Quote
Old 17th April 2003, 04:21 PM   #12
diyAudio Member
 
cdwitmer's Avatar
 
Join Date: Apr 2003
Location: Tokyo
Default Here's the left half of the schematic

Here's the left half of the schematic.
Attached Images
File Type: jpg m955left.jpg (30.3 KB, 305 views)
  Reply With Quote
Old 17th April 2003, 04:33 PM   #13
diyAudio Member
 
cdwitmer's Avatar
 
Join Date: Apr 2003
Location: Tokyo
Default Oh yeah, this amp's model is M-955N II / 260

The Onkyo M-955N II / 260 was introduced in 1975.

Yamaha produced something similar, the B-4, in 1978. Probably other Japanese manufacturers had similar offerings, since most of the manufacturers liked to imitate each other.

The thing is just shy of 20 kilos.

It's just a simple, no-nonsense amplifier, at least from the user's perspective.

It didn't cost me very much so I don't have to have a heart attack if I allow the musical smoke to escape from inside the components while trying to repair it -- although I certainly don't want to ruin it since we don't see these old amps as much as we'd like.

God bless and good night!
  Reply With Quote
Old 18th April 2003, 10:42 AM   #14
diyAudio Member
 
mrfeedback's Avatar
 
Join Date: Feb 2002
Location: Perth, Australia.
Default Rare Classics...

Quote:
Originally posted by jcarr
CDWitmer:
Your amplifier looks very nice. The Class A operation and monaural power supplies suggest that it belonged to Onkyo's premium series. That being the case, I wouldn't be surprised if it includes other technical features that are quite interesting, even by today's standards. It may even be an early MOSFET or vertical power FET design.
Hi Jonathon,
I have an Onkyo amp from similar era, and similar quality level for it's day.

It is high bias AB design, with two power transformers and four filter caps, and about 100w+100w I expect.
The pre-amp stage has a switched tone control stage (bass and treble selectable turnover frequency switches and boost/cut rotary switches) using caps like 10uF solid caps (size of a matchbox).

The front panel is full of features like pre-amp -20dB mute, power-amp in 0/-10/-20 dB attenuation, Dc/0.1/20 Hz coupling, High cut, Low cut, 2 loudness contours, Stereo/Reverse/L+R mono/L mono/R mono, switchable phono cart loading etc.

Despite all this signal switching and routing, this amp is one of my favorites for all round pleasantness and musicality, and trounces many other amps regardless of age.

Yes, Onkyo did make good and solid (heavy) gear back then, and I would say that these sorts of amplifiers are well worth collecting and renovating.

Eric.
__________________
I believe not to believe in any fixed belief system.
  Reply With Quote
Old 18th April 2003, 12:16 PM   #15
diyAudio Member
 
Join Date: Mar 2001
Location: Brazil
Default Re: Here's the left half of the schematic

Quote:
Originally posted by cdwitmer
Here's the left half of the schematic.
Can we have a look at the rest of the circuit?

Have you tried doing B & W scans instead of gray scale? Files may be smaller in that way.

Lately I have looking at some Harman Kardon circuits, available from HK's site, particularly models HK770 and HK775, which are power amps that I listened to and liked. The circuits are quite interesting, as they are pure DC with no servo or feedback blocking capacitor. It deserves a look if you have some time.



Carlos
  Reply With Quote
Old 18th April 2003, 01:02 PM   #16
diyAudio Member
 
cdwitmer's Avatar
 
Join Date: Apr 2003
Location: Tokyo
Default Hi-res scan of complete schematic

Clicking on the following links should take you to two scans of the complete schematic. They are black and white, 300dpi, in GIF format.

These are posted at a Japanese website, and your browser will probably "complain" or ask you if you want to download a plug-in to be able to read Japanese on your computer. If you just answer "No" to that error message, the image should display just fine. The image will be displayed in a frame, but if you right-click on the image, you can open it in a new window of its own or download it to your computer for printing.

Each half of the schematic fills an A4 or letter-size sheet of paper if printed at 300dpi.

Also, the free site where these are posted gets busy at certain times of the day, so if you have trouble accessing, it probably means it's a peak traffic period for that site.

If there are any problems, please let me know.

Here's the left side of the schematic

Here's the right side of the schematic
  Reply With Quote
Old 18th April 2003, 04:38 PM   #17
jcarr is offline jcarr  United States
diyAudio Member
 
Join Date: Jul 2002
Location: Tokyo, Japan
CDWitmer:

Entirely possible that we have met before. I have since moved to Setagaya, right outside of Shimokitazawa, but everything else is as you remembered.

Incidentally, another type of part that commonly fails over time is a switch. And I believe that your Onkyo has speaker output on/off switches, as well as switches for Class A and Class B operation. It is possible that one of these has started to go. Ditto for volume pots.

best, jonathan carr
__________________
http://www.lyraconnoisseur.com/, http://www.lyraaudio.com
  Reply With Quote
Old 18th April 2003, 05:29 PM   #18
diyAudio Member
 
nemestra's Avatar
 
Join Date: Jul 2002
Location: UK
Default Re: Need advice on replacing caps in amp P/S

Quote:
Originally posted by cdwitmer
This component has three connectors, "Plus," "E," and "Minus"; it is marked with the values "15000uF + 15000uF 80WV."

Since I have enough room and since I found a cheap source of computergrade capacitors, I am thinking of replacing this component with an array of six identical 12000uF 80V capacitors. (For example, creating two 36,000uF parallel chains and then joining the two chains in series would be one possibility.) Other configurations are also possible, and it would also be possible to use only four of these capacitors rather than six.

Here are my questions:
1) What is the best strategy to take here? Four capacitors? Six? What configuration?
2) Do I need to use balancing resistors? If so, how should I use them?
Thanks for posting the schematic. The centre terminal of the capacitor goes back to a tap on the transformer and so this is a conventional full wave bridge. Balancing resistors are not required in this arrangement.

As for the number of capacitors I would be tempted to replace each capacitor initially with four of your new ones. This gives a capacitance of 24000 uF per half of the old 15000 uF cap which is closer to the original value as designed. The only reason not to use six for each cap is that the charging current through the diode bridge will increase as you add capacitance. Most bridges will cope with the extra current pulses ( which are quite short - a low duty cycle ) so you may be okay with the extra caps.

Hope this is understandable - I can draw you out the capacitor arrangement if required. Joe Dirt has also offered earlier in the thread, I think.

James
  Reply With Quote
Old 18th April 2003, 10:00 PM   #19
diyAudio Member
 
cdwitmer's Avatar
 
Join Date: Apr 2003
Location: Tokyo
Default Thanks again, Jonathan & James

Yes, Jonathan, I shall check out those other parts that you mentioned. Thanks for mentioning that.

James, I appreciate your confirmation on the earth connection and lack of need for balancing resistors, as well as the suggestion that I try four caps first rather than six. I had been thinking the same thing; even with four I'll end up with something much beefier than before, and I'll not stress the other components so much.

I find it interesting that, providentially, there happens to be another inquiry, posted at almost the same time as mine, that directly applies to mine.

It's thylantyr's "Capacitor Question - Amplifier/Power Supply."

I guess "it never rains but it pours."

You've all be a great source of help and encouragement. I'll report on the outcome!
  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
Need advice replacing caps in Harmony H400a guitar amp tonebrulee Instruments and Amps 11 22nd May 2010 01:06 PM
Replacing multi-section caps with multiple caps? Sir Trefor Tubes / Valves 1 29th May 2007 10:17 PM
Any advice on replacing SMD Opamps PHilgeman Parts 5 1st April 2004 01:34 PM
Replacing ceramic disc caps with silver mica caps? G Solid State 5 18th November 2002 01:02 PM


New To Site? Need Help?

All times are GMT. The time now is 09:32 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