Go Back   Home > Forums > >

Solid State Talk all about solid state amplification.

Toshiba 330 power amp issue
Toshiba 330 power amp issue
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
Old 26th October 2017, 01:34 AM   #1
peacocksuit is offline peacocksuit  United Kingdom
diyAudio Member
 
Join Date: Feb 2012
Default Toshiba 330 power amp issue

Hi. I have been using a late 1970's Toshiba Toshiba 330 separates for the past few years. When I got the the amp it needed a pair of transistors replacing which I did myself. It has worked faultlessly ever since.

Recently I have noticed that the right channel has been 'dropping out'. I get hardly anything from the right side speaker, just a very quiet distorted playback. After trying lots of things to try and find whats wrong I realised that If I turn the power off and turn it back on the problem goes away. The amount of time it takes to 'drop out' again is varied, but as soon as I touch the power toggle switch I get the sound back in the right channel. It takes a few seconds on this amp before the sound gradually fades to nothing which is how I discovered that cutting the power 'fixes' the issue (temporarily).

My knowledge of electronics is limited but I understand the basics and I'm reasonably handy with a soldering iron.

I a guessing that this is something to do with a dodgy capacitor?

I'd be really greatfull if anyone can advise further, I love my old HiFi setup and would really like to keep it going for as long as I can!

Thanks for reading my post, thanks very much in advance for any help
  Reply With Quote
Old 26th October 2017, 02:20 AM   #2
Ian Finch is offline Ian Finch  Australia
diyAudio Member
 
Join Date: Apr 2010
Location: Coffs Harbour, NSW
Toshiba 330 power amp issue
You're almost right about dodgy parts. The symptoms you describe suggest the speaker relay (aka output relay) is the problem. Its contacts are likely dirty due to contamination or by a slow accumulation of arcing refuse etc. When you turn off and repower the amplifier, the contact is remade and this probably dislodges a little of the debris, making a fresh but only temporary contact. If the relay cover is removable, you may be able to clean the offending contacts with a small strip of card drawn between them - do not use an abrasive other than an ultra-fine treated paper type intended for the purpose.

Otherwise, the simplest remedy would be to replace the relay with a similar type, having the same footprint and contacts which you can search by drawing dimensions, from a major parts supplier like Farnell, RS components or CPC. There is a little more to that, as the coil voltage and contact current ratings must be met or bettered too.
  Reply With Quote
Old 26th October 2017, 10:00 AM   #3
peacocksuit is offline peacocksuit  United Kingdom
diyAudio Member
 
Join Date: Feb 2012
OK, Ian. I will look into this as first point of call. Thanks! I may be worth noting that when the channel drops out, there is still some activity audible on it, but its extremely quiet and muffle, and intermittent. Is it worth noting that switching to mono will play audio from both channels?I suppose you would expect that but thought I might just mention it....

Thanks again, mate.
  Reply With Quote
Old 26th October 2017, 10:10 AM   #4
peacocksuit is offline peacocksuit  United Kingdom
diyAudio Member
 
Join Date: Feb 2012
Also forgot to mention that when the right channel does drop out, the headphone output operates as normal. I ruled out any issue with the signal leaving the pre amp by testing this.
  Reply With Quote
Old 26th October 2017, 10:15 AM   #5
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Toshiba 330 power amp issue
I remember your original thread on this.

As Ian suggests, this does sound a little like relay troubles. Typically if that is the case then turning the volume up can often 'fix' the issue for that particular listening session as the higher current punches a way through the oxidation.

Does this amp actually use a relay ? If it did then the sound should not fade out as you turn off...... so I suspect not from your description.
  Reply With Quote
Old 26th October 2017, 10:19 AM   #6
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Toshiba 330 power amp issue
It doesn't have a relay.

Possibilities includes the speaker selector switch. Give it a good whizz to and fro. Also don't discount the speaker fuse holders and even the relevant fuse (once had one with the wire not soldered internally and it was making just a point contact).

Try those first.
  Reply With Quote
Old 26th October 2017, 10:29 AM   #7
peacocksuit is offline peacocksuit  United Kingdom
diyAudio Member
 
Join Date: Feb 2012
Hi, Mooly. You helped me fix this amp last time, I'm still really greatfull
I tried the speaker selector switch as you described last night, in fact, I gave all the switches a good move back and forth several times, nothing seems to remedy it other than turning the power off, even after a split second it 'clears' the problem for a short while. This amp has speaker 'A/B/Off' selector, I have tried the speakers in both A and B outlets, the problem persists.

I will crack the case open this afternoon. I have a can of servisol somewhere so I will give all the switches etc a good 'drink' and operate them excessively while the amp is off. I'l also check the fuse carriers and fuses as suggested.

Will post up any findings! Thanks very much.

Last edited by peacocksuit; 26th October 2017 at 10:35 AM.
  Reply With Quote
Old 26th October 2017, 10:37 AM   #8
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Toshiba 330 power amp issue
It sounds a bit of an odd one from what you describe. Any drastic fault would upset the DC conditions and you would certainly know about that... so whatever is going on is something subtle.

When the fault occurs, does physical movement or impact or prodding the PCB have any effect ?

If you don't find anything obvious then you have to resort to basic checks at key points in the circuit. A good check in this case would be to confirm that the output stage is drawing current which is easily done by measuring the voltage dropped across the 0.47 ohm emitter resistors.

See what you find first and gather as much evidence as you can.
  Reply With Quote
Old 26th October 2017, 10:44 AM   #9
peacocksuit is offline peacocksuit  United Kingdom
diyAudio Member
 
Join Date: Feb 2012
Ok, Mooly. I tried sort of prodding all the switches/pots but nothing seemed to make a difference. I also wiggled all the leads, the output lead from the pre amp is soldered in and RCA plugs at the other end, I suspected that at first but it doesn't seem to be at fault, and the headphone output working ruled that out as well. During 'fault conditions' the watts power gauge needle read barely anything on the right channel. I will see how things look inside anyway and maybe get some pics.
  Reply With Quote
Old 26th October 2017, 10:53 AM   #10
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Toshiba 330 power amp issue
Does the power meter read correctly when just using headphones ?

Definitely worth looking at the fuse/holder as a first step.
  Reply With Quote

Reply


Toshiba 330 power amp issueHide this!Advertise here!
Thread Tools

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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Toshiba TK70J20D power MOSFET Karl vd Berg Parts 0 6th August 2016 01:21 AM
F5 Toshiba Output bias Issue DGreen Pass Labs 14 24th August 2015 10:20 PM
Memphis Power Reference 16-PR1.1000 power issue, HELP??!! TCCustoms Car Audio 3 27th June 2013 01:58 AM
6GB8 Toshiba power tubes rjm Swap Meet 2 22nd November 2010 08:04 AM
Toshiba power BJTs now at digikey mirlo Parts 8 28th February 2003 08:46 PM


New To Site? Need Help?

All times are GMT. The time now is 01:46 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Copyright ©1999-2021 diyAudio
Wiki