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Power supply temperature Pioneer SX-1080

mieuba

mieuba

New Member
I´ve owned a Pioneer Sx-1080 receiver for two weeks now that is in very good condition. I had noticed that the heat disipators (with "U" shape) in the power supply assembly run at high temperature. May someone tell me anything about it? Thanks.
 
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It's for the most part normal. The transistors attached to the heatsinks are running flat out and putting out a lot of heat. This is common with a lot of 70's PIONEER gear. You can relieve some of the heat with a quiet table fan about 12" away from the unit blowing air in it's direction. If you know how to check / adjust the bias and offset (grab the manual and read the directions for adjusting the amp) check to see if the settings are in spec. If not, then if you feel comfortable with it, adjust to the specification listed in the manual. That may bring down the temps a little.
 
Thanks for your repply! I made today measurements with infrared gun and multimeter. With the infrared results are running between 81 and 90 ºC in the core and between 72º and 81 °C at the base. By measuring with the thermocouple the hottest is 101 °C . The amplifier sounds great.
Hear , enjoy and pray ... Greetings from Buenos Aires!!
 

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72*C = 161.6*F
80*C = 176*F
101*C = 213.8*F

I thought you were speaking about the OUTPUT Transistors. But the small one's will run hot also. Check for voltage on the heatsinks (dissipators). The base of the transistor on those TO-220 types are connected to the back making the heatsiks "hot" in more ways than one.

There are commerically available heatsinks that are larger and have fins on them to dissipate more of the heat efficiently, and cool the transistors down some. Also if you use mica insulators and nylon screws and nuts from the transistor to the heatsink you can isolate the heatsink from the base and it's electrically cold at this point (No Voltage). Anything you do to cool the components down is ultimately GOOD.
 
I know, it is very high temperature and, therefore, a lot of hot! I was reading and researching this issue and the conclusion is that is common to all Pioneer's power supplys of those years. Particularly aggravated in the SX-x80 line. Here one example:
http://audiokarma.org/forums/index.php?threads/sx-980-power-supply-heat-sink-temperature.526499/
The hot transistors in my SX-1080 are 2SD712, the Tj for these are rated between 150 - 180 ºC that is Pioneer design a toaster but in range!!
I sincerely appreciate your advice!
For now I'll wait a while to think because the receiver works great. Surely soon I'll have a way to improve the problem.
Thanks and Greetings!
 
The devices will last a lot longer and provide more stable service at less than 50°. As Larry mentioned, there are some fairly easy methods to cool things down:

Here is a similar regulator with the original heat sink:
SX-780-DQ25OEM.jpg




And the same unit under the same conditions with an add-on heat sink:
SX-780-DQ25Modified.jpg
 
Yes, many Pioneer models are known for running very hot pass transistors in their regulated power supplies. On my SA-9900, there is a 21 volt drop across each of the pass transistors resulting in a power dissipation of around 2.5 W which is a lot given the size of the tiny heat sink used. I measured just over 100 deg C after only 10 minutes of operation. So, I decided to borrow a page from @EchoWars playbook and I moved the two pass transistors to the large heat sink which resulted in a dramatic temperature drop to 36 deg C. The large sink soaked up the heat without any noticeable rise in temperature.

Here is the link to EchoWar’s thread outlining the modification as performed on an SX-1980:

http://www.audiokarma.org/forums/index.php?threads/pioneer-sx-1980-regulator-modification.618700/

Les.
 
Surely is not cute. But is a very effective and easy solution! A fan (exhaust), ball bearing and powerful (20VA), connected to the switched output of the receiver.
Easy to remove if you want to show your gear and easy to reinstall for you peace of mind.
20160824_170249.jpg20160824_171615.jpg
 
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Fans will tend to attract dust, making it necessary to open the unit up and vacuum on a regular basis to keep it clear. Dust acts as insulation and will keep the heat in and can also become conductive and cause problems in that way. Adding the heatsinks will do the better job. Nice receiver BTW.
 
Today I made measurements to observe the results of the cooler on the temperature in the transistors of the power supply. The improvement is really important. Temperatures have dropped 30 ºC as you can see in the photographs. I think it's really a simple and effective solution.
20160827_093738.jpg 20160827_093821.jpg
 
Hi friends.
Sorry for intruding on this thread. But I have a problem on my pioneer sx 1080.
what would be a replacement transistor for the bd682, from power supply?
thank you for your help
 
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How about a 2sd682 i’d have to look at its specs but many npn subs would work, guessing ksc2073, mje15030,32 etc
 
Okay then I did not look at specs for a bd682 and assumed you thought it was a d682 something.
So some one subd that from the original which? according to the service manual is? But your sub list is okay I guess, without me looking further
 
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