Pioneer SA-9800 Repair And Restoration
This Pioneer SA-9800 integrated amplifier is in pretty rough cosmetic shape and was put out to pasture many years ago.
Lots of dirt and dust to remove from the case which is not uncommon when you are repairing or restoring vintage stereo equipment.
The faceplate also has years of old grime that needs to be cleaned up. Warm water and some dish soap will clean it up.
I now have removed the top cover of this Pioneer SA-9800. Some cleaning to be done on the chassis also.
I've moved outside to get the dust out. The garbage can makes a good table. A paint brush and some compressed air will help.
The paint brush works well to clean up the grime from areas like these transformers.
I'll get the worse of the grime off of the faceplate while I'm outdoors. Better then having all of that crap inside.
The function switch shaft is broken off. No.....it's not just the knob that is missing. The good part it that the switch internally is still intact.
Always have the service manual for the Pioneer SA-9800 before you attempt any adjustments.
When powering up an unknown solid state amplifier check the dc offset at the speaker terminals without speakers attached. 252mv on the left channel.
The dc offset should be close to 0V. I was able to adjust it down on this Pioneer SA-9800 integrated amplifier.
I noticed that the right channel power transistors heatsink was warmer to the touch then it should be after a short warm-up.
The idle current was higher then it should on the right channel of this Pioneer SA-9800.
Using the Pioneer SA-9800 service manual I was able to set the idle current to specifications which took care of the warm heatsink.
Now I've finally hooked up speakers to this Pioneer SA-9800 and I can hear a fairly loud hum from both channels
The power supply assembly located at the underside of the Pioneer SA-9800 integrated amplifier is suspected of causing the hum.
Pins 1 and 2 on the power supply assembly (AWR-191) are at -72 volts. These pins should be around -52 volts.
When measuring voltage inside a tight area like this Pioneer SA-9800 put some electrical tape around all but the very end of the probe.
The measuring points are very close together and if you slip (and you will some day) there is less of a chance of you shorting something out.
Take your time and go slow. Shorting leads together on this assembly will probably not end well for your Pioneer SA-9800.
I have printed out the one page from the service manual that I need for troubleshooting the power supply assembly.
After I made my way to the section of the assembly that I thought was causing the issue I saw a transistor with a large crack in it.
I will remove the cracked transistor. I use a Hakko 808 unsoldering tool. It's a great tool if you unsolder a lot of components.
I also have a stash of transistors. I hate having to wait on ordered parts so I keep most of the common ones in stock.
I've removed the cracked transistor from this Pioneer SA-9800, I'll use a transistor tester made by the PEAK company in the UK.
It's not a huge surprise that the cracked transistor is dead to the world as the DCA75 tester says "No component detected".
When you find a transistor with physical damage you should think that this may have been caused by another defective component.
I've removed another component. The K34 FET in the picture below is rare and I was hoping that this FET would test good.
Fortunately it did test good. Testing a FET accurately can be tricky with a multimeter. The DCA75 tester takes out the guess work.
This 1735 is another transistor that I have removed for testing from this Pioneer SA-9800 integrated amplifier.
The tester sees this transistor as a diode so a section of this transistor has failed and it will need to be replaced.
There is one other A904 that showed no physical damage but that I need to test.
This transistor also is bad. So a total of two A904's transistors along with one 1735 will need to be replaced.
With the three transistors replaced we now have -52 volts on pins 1 and 2 of the power supply assembly. The hum is now gone.
Almost any vintage audio repair or restoration will involve cleaning the pots and switches with deoxit.
Some disassembly of the Pioneer SA-9800 is necessary to properly clean the pots and switches.
I've got the controls back in the chassis and I'll give the SA-9800 a quick check to see that I didn't cause an issue when I had the assemblies removed.
I've cleaned up the faceplate and have reinstalled it along with the knobs on this Pioneer SA-9800.
I'll have to figure out something for the function switch issue but for now this Pioneer SA-9800 repair and restoration is complete.