Pioneer SA-408 amp Testpoint question - UK Vintage Radio Repair and Restoration Discussion Forum

gboshoff · 10th Sep 2020, 8:05 pm

Hi I am new here and I have a question.
If you look at the pioneer sa-408 amplifier you will see that there are 4 test points
what is the correct voltage to expect at the test point?

thank you in advance for any info
much appreciated

Radio Wrangler · 11th Sep 2020, 10:13 am

Welcome!

I don't expect many people will have that model to be able to take a look, but I've downloaded the schematic from Electrotanya and there are four prominent test points on it.

They are there just to allow the quiescent current to be set up. With no signal going through it, you measure the voltage between TP1 and TP2 and there will be a quiescent current adjustment potentiometer somewhere that can be adjusted if the voltage is not within the limits printed in the manual.

To find what that voltage is, you'll have to search for the service manual, but 20mV would be a guess.

The voltmeter you use must be fully floating - no connections to anything else

Take care when going in with a screwdriver that you don't short anything or drop it onto the board.

This amplifier actually uses discrete transistors and is repairable. Later models went over to using highly integrated 'STK' series modules, and those are hard to find replacements for.

David

gboshoff · 17th Sep 2020, 12:26 am

Thank you for the information esp on how the testpionts work

10th Sep 2020, 8:05 pm	#1
gboshoff Diode Join Date: Sep 2020 Location: Port Elizabeth, Eastern Cape, South Africa Posts: 2	Pioneer SA-408 amp Testpoint question Hi I am new here and I have a question. If you look at the pioneer sa-408 amplifier you will see that there are 4 test points what is the correct voltage to expect at the test point? thank you in advance for any info much appreciated

11th Sep 2020, 10:13 am	#2
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,876	Re: Pioneer SA-408 amp Testpoint question Welcome! I don't expect many people will have that model to be able to take a look, but I've downloaded the schematic from Electrotanya and there are four prominent test points on it. They are there just to allow the quiescent current to be set up. With no signal going through it, you measure the voltage between TP1 and TP2 and there will be a quiescent current adjustment potentiometer somewhere that can be adjusted if the voltage is not within the limits printed in the manual. To find what that voltage is, you'll have to search for the service manual, but 20mV would be a guess. The voltmeter you use must be fully floating - no connections to anything else Take care when going in with a screwdriver that you don't short anything or drop it onto the board. This amplifier actually uses discrete transistors and is repairable. Later models went over to using highly integrated 'STK' series modules, and those are hard to find replacements for. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

17th Sep 2020, 12:26 am	#3
gboshoff Diode Join Date: Sep 2020 Location: Port Elizabeth, Eastern Cape, South Africa Posts: 2	Re: Pioneer SA-408 amp Testpoint question Thank you for the information esp on how the testpionts work