broken amp - 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 22nd February 2006, 03:53 AM   #1
diyAudio Member
 
Join Date: Feb 2006
Location: -
Angry broken amp

Hi folks - don't know if i'm in the right section but i bought a technics SU-7700 integrated amp recently on ebay and it's died already and i haven't a clue what the problem is with it. It's impossible to find anyone in my part of the world who would be able to fix it and i was wondering if anyone had any ideas. I was using it this time last week and the speakers went dead - it kicked back in a few minutes later and repeated this a couple of times over the next 24 hours and then died for good. The lights in the VU METER windows stayed on and the very low hum that's audible when it's on is still there, it just doesn't seem to be delivering to the speakers. i checked what i could re fuses and connections and couldn't find anything though my knowledge is pretty basic in this dept. It did normally take a couple of minutes to warm up in the morning and had recently been making static noises when adjusting the volume though i understand this isn't unusual in old amps. I'm really fond of this amp and would hate to see it go to waste esp if the problem is something simple. Can anyone help me? Many thanks
  Reply With Quote
Old 22nd February 2006, 10:46 AM   #2
diyAudio Member
 
Join Date: Jul 2003
Location: Dona paula, Goa
U have dry solder problem due to heat.
Search for dry solder on DIYAUDIO, u will find so many answers.

Gajanan Phadte
  Reply With Quote
Old 22nd February 2006, 02:24 PM   #3
jaycee is offline jaycee  United Kingdom
diyAudio Member
 
Join Date: Apr 2004
Location: Norwich, UK
... or theres a fault in the speaker protection circuit which has caused it to disconnect the speakers permanently. There's usually a startup delay which is a simple RC timer, if the capacitor dries up, it kills the protection circuit which makes the speakers stay switched off.
  Reply With Quote
Old 22nd February 2006, 02:37 PM   #4
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
Default Re: broken amp

Quote:
Originally posted by madmadra
very low hum that's audible when it's on is still there, it just doesn't seem to be delivering to the speakers.
Is this hum from the amp itself or coming out the speakers? If it's coming out the speakers it cannot be the startup delay.
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more.
  Reply With Quote
Old 22nd February 2006, 03:51 PM   #5
diyAudio Member
 
Join Date: Feb 2006
Location: -
Thank you - anyone know where this problem is usually located? and any advice on fixing it - i'm not a techie and would need it explained to me like i'm 5
  Reply With Quote
Old 22nd February 2006, 05:17 PM   #6
diyAudio Member
 
Join Date: Feb 2006
Location: -
No the hum is from the amp, barely audible. i'll attach a photo - if it's a dry solder prob can someone point out the location to focus on - many thanks
  Reply With Quote
Old 22nd February 2006, 05:17 PM   #7
diyAudio Member
 
Join Date: Feb 2006
Location: -
sorry forgot the photo!
Attached Images
File Type: jpg amp smaller.jpg (77.5 KB, 497 views)
  Reply With Quote
Old 22nd February 2006, 06:05 PM   #8
Bobken is offline Bobken  United Kingdom
diyAudio Member
 
Join Date: Dec 2002
Location: UK
Hi,

I don't know anything about this particular amp., but from what you say, this could be a problem with the 'wiper' going open circuit on the vol control, especially if it is as old as you suggest.

This could explain the intermittent static noises you mention when operating the vol control, and would more than likely give rise to some hum as the input to the first stage would probably then be open-circuit.

However, I assume it is a stereo amp, and it would be unusual for the same problem to occur (at one and the same time) in both channels.

Did both channels work OK when you first tried it out, and immediately before it finally died?

Edit. I just realised you later said the hum was from the amp, not the speakers, but a slight hum from an amp is not unusual, anyway. However, if the problem is with both channels, this is significant as it is unlikely that both channels of the amp boards would die together.

You would then need to consider any 'shared' parts of the circuit more like the power supply, perhaps.
__________________
Bob
  Reply With Quote
Old 24th February 2006, 01:51 AM   #9
diyAudio Member
 
Join Date: Feb 2006
Location: -
ok thanks Bob - i'm going to have to try to get someone to have a look - i wouldn't know where to start - it's very difficult to find anyone around here who fixes electronics that are not new or under warranty - i just thought someone here would be able to point me in a def direction where i could go at it myself - many thanks to all who offered their help - it was much appreciated

ps, if it's a dry solder problem, where would it most likely occur in this instance?
  Reply With Quote
Old 24th February 2006, 02:59 AM   #10
clem_o is offline clem_o  Philippines
diyAudio Member
 
Join Date: Jun 2005
Location: Manila
Dry solder joints can occur anywhere, there is no "more likely place". Unfortunately, any bad connection on the amplifier board can cause the symptoms you've described.

Could even be a bad coupling capacitor. It could introduce a DC offset at the output of one of the amplifiers, causing the speaker relay circuit to cut out (protection).

If you have a DVM handy you could try measuring voltages; that would be a starting point but you'd have to have a schematic and know how to read it (i.e. people here could tell you where to measure on the schematic, but you'd have to have a basic electronics background to be sure you're measuring the right point on the actual amplifier...

Cheers!
  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
Broken sub amp RiverGmblr Solid State 37 6th November 2005 03:38 PM
What's been broken? Tubesin Tubes / Valves 1 29th June 2005 11:54 AM
Broken CD HELP! Bassivus Digital Source 8 29th September 2004 09:46 PM
broken amp BrokenBC Car Audio 6 5th February 2004 10:31 PM


New To Site? Need Help?

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