• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Technics SA-800 question

HBM

HBM

New Member
Thanks for taking time to read my first post!

I have a Technics SA-800 and am trying to find information about the temp sensors on each heat sink. One has broken wires at the sensor/thermistor. Will the amp continue to work? I can't find these on the schematic or I would get a replacement/ substitute.

Thanks again in advance.
 
Register to hide this ad
Welcome to AK!

My guess is you are looking at D605 & D606. Does that sound right?

Assuming this is right, and assuming no one comes along with a better idea, you could try figuring out a way to package a string of four small-signal silicon diodes (such as 1N4148) into some kind of unit that you could attach to the heat sink. Some have used a ring terminal and "JB Weld".

Or you could try to find a reliable supplier of a part generally known as STV4H. I don't know the prospects of this.

HBM said:
Will the amp continue to work?
Click to expand...

Again assuming we are talking about D605 or D606, their function is to regulate idling current in the the driver and output transistors. With those diodes open-circuited, currents will be disastrously high if the amp is powered on. If that has already happened, I'm sorry to say that you probably have more damage to track down than just the broken diodes.

Along the same lines, you will want to at least clean, or perhaps replace the idling current adjustment resistors, VR601 and VR602. Flaky contacts in those parts will also result in severe overcurrent.

It will help to prevent further damage if you test the amp using a "dim bulb tester". You can find info about DBTs here on AK or probably many places on the interwebosphere.
 
Thank you! You are spot on. I found an SVT-3H. Can't find an SVT-4H. Can't determine from the info I have which one is used in the SA-800. If anyone has any recommendations Please let me know.
Thanks again.
 
There is a whole thread about "re4placing the STV-3 and STV-4 diodes". Please search AK.

To replace the STV-4H, you usually need 3 x 1N4148 in series. Four diodes will have a too high voltage drop and bias won't go down enough.

Read the referred thread to see different ways of mounting the diodes array, and try 3 diodes in series. If bias stays too high, try 2 diodes.
 
HBM said:
Can't determine from the info I have which one is used in the SA-800
Click to expand...

If the service manual I pulled from elektrotanya is to be trusted, it's definitely the STV-4H.

From the hands-on reports above, it sounds like my suggestion of replacing with a string of four 1N4148s was wrong. If going this route, try a string of three, per elnaldo's suggestion.
 
3 x 1N4148 diodes should be close enough (you have an adjustment pot after the diodes to adjust small differences). The details are in the linked thread. I did it a couple of times in different amps and 4 diodes was always too much.
 
The one in question has already been replaced)previous to me) and is smaller than the original on the other side. Could they habve replaced with a 3 and re-biased?

btw, my Pioneer SX-1280 is in for a full restore and this is my "back up". Hate to call It dead as It was restored once. It is a great unit.

thanks again to all.
 
You must log in or register to reply here.
Back
Top Bottom