• 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

Barn find Sansui AU-7900

GrisPato said:
Apologies for the late response, hav early shift this week so was gone already.
The DC-offset of 30 mV is quite good so no problems there.
2000m is the same as 2 Volt.
What you could do after this measurement is shut it off and measure the voltage divider for the bias transistor. R23,25, vR1 and R 24,26 and vR2.

View attachment 2603726

So each resistor individually and the parts marked in the picture
Click to expand...
It’s ok! I’m just grateful to have you with me through this! I’d be lost without you. Ok. So power off, we are checking resistance since power is off? Or voltage?
This is red lead on one end and black lead on the other end?
What setting on the MM should it be on? Sorry for all the questions I’m just excited. I want this to work so badly.
 
GrisPato said:
Yes, resistance, correct.
Range of DMM on 20k and move it to 2k, 200 of you're not getting enough resolution.
Click to expand...
Ok. Power off. MM set at 20k ohms.
R23 measures 4.67
R25 measures 0.66
VR01 measures 0
R24 — haven’t located yet
R26 measures 0.65
VR02 measures 0


Still have to find R24
 
Here it is, in front of vR2.

Screenshot_20220629-171722_Moon+ Reader.jpg

I would like to know the resistance from one lead of R24 ( circled in red) to one lead of R26 ( circled in red) compared to R24 (which should be 4k7).
 
When you get inconsistent readings here it points to the vR1. But because you could set the bias for the right channel I would expect that to measure good and only the left channel (vR1) being intermittent.
 
GrisPato said:
When you get inconsistent readings here it points to the vR1. But because you could set the bias for the right channel I would expect that to measure good and only the left channel (vR1) being intermittent.
Click to expand...
Ok from r24 to r26 at 20K on the MM on the correct leads it measures 1.10
 
GrisPato said:
And then R23, R 25 for comparison
Click to expand...
At 20k on the MM r23 to r25 measured 5.78. That is if I’m going from the correct leads. The resistors are placed side by side vertically, I measured from the two bottom leads.
 

Attachments

  • image.jpg
    image.jpg
    72.6 KB · Views: 4
That is ok. You're just including R23, when we take that 4k7 off we have 1.07 Volt.
If you can get this measurement but with vR1 turned a quarter clockwise.
 
So practically no change.
Could you try to measure vR1 with different positions ( remind the one position you started with yesterday)
From leg 1-2 should be 0 ohm, from 2-3 should measure 470 Ohm with the trimmer turned clockwise and close to 0 turned counterclockwise.

Screenshot_20220629-220044_Moon+ Reader.jpg
 
Last edited:
You must log in or register to reply here.
Back
Top Bottom