Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Solid State Talk all about solid state amplification.

Technics SU-A808 triping
Technics SU-A808 triping
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 June 2017, 07:07 PM   #1
sNickMercury is offline sNickMercury  United Kingdom
diyAudio Member
 
Join Date: Jun 2017
Location: Gloucestershire
Default Technics SU-A808 triping

Hi Folks.

This is my first post to this forum. So it's nice to meet you all.

I have a Technics SU-A808 which sounds great most of the time. But sometimes the safety circuit kicks-in and resets the amplifier. Then it comes back on and works like normal again.

Now I'm an Electronics Design engineer by trade, but not in audio. By business is Temperature & Humidity Measurement and Logging.

I puchased the Technics Service Manual online, thinking it would give lots of information. But apart from the circuit and a parts list, it's lacking good description.

The fault occurs when cold or hot. I have heated with a hair dryer and it doesn't trigger the error, and cooled with freezer spray and no change.

I have removed the board, and re-soldered the SVI3205B Power Amp Modules. The soldering looks very dry and cracked, and I thought this was the issue. But it made no difference.

Both main rails look ok at -50 and +50V.

I guess the safety circuit is tripping because there is to much dc on the speaker output.

The manual talks about adjusting the amplifer so output voltage. This is done by injecting a signal of 1kHz, 100mV in to the tuner input. Set Volume to MAX and adjust VR203 (Lch) and VR204 (Rch) for 14.0Vac +/- 0.2V. But I don't think this is effecting the dc output level, just setting up the correct input level to the amp.

When the trip occurs it can happen a couple of times in a row, but something many hours between. To I can't see any errors.

I guess I could discount the speakers, then disable to safety circuit, and when the error occurs try and check the voltages. But I risk damage to the amp.

Any advice out there?

How reliable are the SVI3205B Power Amp Modules, and how available are they. I would hate to bin this amp, the sound is just perfect for my old ears. It sounds great when playing my DVD-Audio Queen music through it.

Thanks for responses in advance
sNick
  Reply With Quote
Old 22nd June 2017, 07:19 PM   #2
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
diyAudio Member
 
JonSnell Electronic's Avatar
 
Join Date: Dec 2012
Location: The Jurassic Coast, England. GB
If you clip your dual beam scope to left and right outputs, monitor the DC fluctuation and you will know which SV to change.
__________________
Support for Fender, Marshall and all Valve Equipment; Audio Innovations, Audiorama FU29, Quad and Leak. www.jonsnell.co.uk
  Reply With Quote
Old 22nd June 2017, 07:21 PM   #3
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Technics SU-A808 triping
The SVI3205B as a generalisation could be favourite. I'm not familiar with your amp specifically, however a quick image search shows these to look like the well known 'STK' type modules... and those were always troublesome.

Its quite possible the problem is a dry within the module. Do an image search and you will see pictures of the internals. These are called a 'thick film' type module.

Found a shot here, post #7
http://www.diyaudio.com/forums/chip-...ml#post4647360

Lets say its probably favourite although without more detailed tests it is not 100% guaranteed.

No idea on quality or authenticity of replacements... sorry.
  Reply With Quote
Old 22nd June 2017, 07:28 PM   #4
SVI2004A is offline SVI2004A  New Zealand
diyAudio Member
 
SVI2004A's Avatar
 
Join Date: Mar 2004
Location: Feeding eels in a stream near you
Technics SU-A808 triping
Check 15 v rails - regulator transistors etc, that can cause this fault too
__________________
I remember when amps were amps & speakers were nervous!
  Reply With Quote
Old 22nd June 2017, 07:40 PM   #5
sNickMercury is offline sNickMercury  United Kingdom
diyAudio Member
 
Join Date: Jun 2017
Location: Gloucestershire
Thanks for the fast responses. I will check with my scope, and check the 15V rails.

If the SVI3205B is the issue, do you know of a supplier?

To refresh your minds, the SU-A808 was the amp with the Bamboo Caps and Variable Gain instead of a pot changing the amplifiers input level. To improve signal to noise ratio to 114dB. Mine was manufactured in 1999.

Thanks Folks
  Reply With Quote
Old 22nd June 2017, 09:03 PM   #6
SVI2004A is offline SVI2004A  New Zealand
diyAudio Member
 
SVI2004A's Avatar
 
Join Date: Mar 2004
Location: Feeding eels in a stream near you
Technics SU-A808 triping
3205s extremely rarely go intermittent... most likely external component to SVI

Don't forget to check mosfet v amp rsn6000b for connections
__________________
I remember when amps were amps & speakers were nervous!
  Reply With Quote
Old 29th March 2018, 12:49 PM   #7
John South London is offline John South London
diyAudio Member
 
Join Date: Mar 2018
I have just come across the same Model with a similar fault description.
In this case it was the low voltage power switch on the front panel was intermittent. Very slight movement of the switch and its mounting board would cause the amp to trip. The low voltage switch is similar in design to most push/push tape monitor type switches which often go intermittent/high resistance.

In this case the intermittent contacts were causing the mains power relay to cut which in turn powers everything down for a second while it restarts. This would give symptoms similar to protection relay cutting in.

Plus on this model it is always worth re-soldering the pins on the two hybrid ics and also the two regulator transistors that sit between them.

Hope that this helps
John.
  Reply With Quote

Reply


Technics SU-A808 tripingHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Technics SU-V550 Carlosraj Solid State 0 30th July 2013 11:36 AM
Panasonic SU-2700 Repair (Otherwise known as the Technics SU Z1) MChandler Solid State 22 11th April 2013 07:25 AM
Technics SU-X920D Stephene Solid State 3 12th September 2011 05:10 PM
Technics SU-G95PP1-K aguantesoda Solid State 0 4th October 2007 07:14 PM


New To Site? Need Help?

All times are GMT. The time now is 03:24 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki