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 21st June 2006, 03:59 AM   #1
diyAudio Member
 
tenderland's Avatar
 
Join Date: Jul 2004
Location: us
Default Magic Capacitor

Hello

I am repairing an old Marantz reciever. I have no gain coming out of the rt ch
1 st preamp xistor. I have determined that when I swap the cap from the other chanel (coming off the emiter47uf@50 v) I have gain. Here is the voodo. I replaced the cap and viola no gain. I replaced the same cap in the other ch with a new one -no gain. I only get gain when I use the original old raty cap. Any thoughts. I made certain the polarity is corect


conforzaled
__________________
"If every one is making wheels , why make wheels ? " Steve Jobs
  Reply With Quote
Old 21st June 2006, 03:21 PM   #2
diyAudio Member
 
bikehorn's Avatar
 
Join Date: Aug 2004
Location: toronto
what model is the receiver?
  Reply With Quote
Old 21st June 2006, 03:39 PM   #3
anatech is offline anatech  Canada
diyAudio Moderator
 
anatech's Avatar
 
Join Date: Jun 2004
Location: Georgetown, On
Hi tenderland,
Is the transistor a 2SC458? If so, replace with a 2SC1815. Those early 2SC458's are known to go intermittent.

-Chris
  Reply With Quote
Old 21st June 2006, 08:29 PM   #4
diyAudio Member
 
tenderland's Avatar
 
Join Date: Jul 2004
Location: us
Default ?

The model is 2230 the cap in question is c 754. The circuit will lose gain in either ch unless the original cap is in circuit. I replaced the xistor in one ch but no difference, same same. I checked the print and it definately calls for a 47uf@50. I checked the polarity and it is as in the print.



Thanks
clueless
__________________
"If every one is making wheels , why make wheels ? " Steve Jobs
  Reply With Quote
Old 21st June 2006, 08:47 PM   #5
Netlist is offline Netlist  Belgium
diyAudio Moderator Emeritus
 
Netlist's Avatar
 
Join Date: Jan 2003
Here's the schematic.
Homepage
At least you can measure some DC values to see which are incorrect.

/Hugo
  Reply With Quote
Old 21st June 2006, 10:43 PM   #6
teemuk is offline teemuk  Finland
diyAudio Member
 
Join Date: Nov 2004
Location: Suomi, Finland
I have a theory: Are the original capacitors in open circuit? As far as I see it the sole purpose of those caps is to lower the gain and distortion (I guess). AC bypass to same phase signal instead to the ground attenuates, right? I might be totally wrong.
  Reply With Quote
Old 21st June 2006, 10:53 PM   #7
anatech is offline anatech  Canada
diyAudio Moderator
 
anatech's Avatar
 
Join Date: Jun 2004
Location: Georgetown, On
Hi tenderland,
That cap is in a low impedance position. It would have to be awfully leaky to cause a problem, it is in your feedback loop as a coupling cap. If it were to open, your gain should go up.

Look at R754 and the foil around that area. I would install new caps in both positions if you don't have a cap checker and troubleshoot from there. I'm wondering if the high gain is a fault condition.

C753 and it's mate on the other channel should be checked. I have more trouble with the small 1 uF types. You may be further ahead to just simply replace all the electrolytic caps in the amplifier boards to be honest with you.

-Chris
  Reply With Quote
Old 22nd June 2006, 12:13 AM   #8
diyAudio Member
 
Join Date: Jun 2006
An update where you at in repairing the marantz. I have a similar Marantz and thought about reparing it myself. Let me know. Thanks.
  Reply With Quote
Old 22nd June 2006, 12:24 AM   #9
anatech is offline anatech  Canada
diyAudio Moderator
 
anatech's Avatar
 
Join Date: Jun 2004
Location: Georgetown, On
Hi excetara2,
It's a nice little set. Should last years after you are done.

What's wrong with yours?

-Chris
  Reply With Quote
Old 22nd June 2006, 02:32 AM   #10
diyAudio Member
 
tenderland's Avatar
 
Join Date: Jul 2004
Location: us
Default victory

Thanks all who contributed to this thread.
Thanks Anatech and teemuk whos resonse put me on the corect path. Anatech , right on .The old cap created a fault condition. With all new caps gain ON THE OUTPUT is equal. I am a bit embarased I didnt figure it out.


Thanks again
Jeff
__________________
"If every one is making wheels , why make wheels ? " Steve Jobs
  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
The Magic of a Name 7N7 Tubes / Valves 9 1st December 2007 05:58 PM
Naim magic box ash_dac Everything Else 2 17th July 2006 12:30 PM
6e2 Magic eye datasheet Silver Stealth Tubes / Valves 10 28th November 2005 07:08 AM
Playing with a Magic Eye. Shoog Tubes / Valves 7 13th January 2005 09:33 PM
TAD - the magic drivers? amo Multi-Way 4 12th May 2004 04:49 AM


New To Site? Need Help?

All times are GMT. The time now is 01:24 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