Project/One Solid State Stereo Receiver help.

Right, with out knowing what to adjust bias at its a shot in the dark

the Pioneer www.hifiengine.com/manual_library/pioneer/sx-1000tw.shtml also looks close.

One adjustment pot but it has 2 more transistors on amp board. But the outputs look similar. 

So going on Kurts suggestion I swapped amp boards and adjusted to best I could 5 mv and the higher DC followed the board to the left channel.

So I let it stabilize some more and readjusted best I could to the 5 mV a little over and under on each . I also plugged it into a smart plug to monitor 
wattage use and you can see the change dramatically when I adjust the trimpot to higher bias setting. but its at about 12.4 watts with the bias set between 4.5 and 5.3 mV on each amp.

But here is the weird part. I wanted to hear how it sounds with head phones. Last night I tried and it was horrible. Just now I tried and it sounds not bad, not bad at all.

So I went to look at DC and it was almost to 0 on both channels!! Fluctuating from 23 to 0 mv off and on. WTF??? 

So I removed the head phones and the DC went up as soon as I removed the head phones . Not quickly but at a steady climb to where now the right channel is at 
2 vdc and the left channel( now with the re capped amp board swapped from the right) is at 300 mV !!! that amp board use to go 5 vdc and the uncapped board was at 2-3 VDC .

So what is it about the head phones that lowered the DC? made a video showing slow rise.



nashou

Is there a date sticker on the back of this?

Also, see if you can confirm that this part of the circuit is the same as yours. Not necessarily the values, just the layout.

Without a schematic i could not tell you.

I don't think it matches up exactly. I spent a lot of time marking up the back side of the Amp board . what a pain. should have hand drawn it!!! lol

But Q1 and Q2 are the SD188's left side is Q1 right side is Q2 in this pic

then you should be able to follow the second pic to the first pic, I'll also add the front of the board as the third pic.








I don't think I missed any parts , let me know if you need specific values . I measure some with DMM but then realized they may be off .

some more info , that blue wire that turns to white and goes to Relay board. it goes to board then through a resistor then thought that top diode
and into a transistor, and then to another transistor . Not all clear but I'll need to mark that up too I guess ( the relay board) .

EDIT: I did forget one cap, it is suppose to go at the bottom left corner of my mark up diagram, and in the front pic its the one on the bottom right
corner. Hopefully there arent any others missing.

Athanasios

I think I have an answer here.

Head phone jack is always in play no matter where you have the speaker selector set. On most schematics I looked at
there are high power resistors that reduce the signal for the head phones. So when you insert the headphone a path to GND is created
and this might be removing more DC from the signal. So this has me wondering if on this amp if I have to measure DC at speaker outs while
the speakers are connected? 

Also I might be able to get my probes to the headphone jack and measure DC there before and  after the two 550 ohm resistors. 

So this has me thinking that maybe its those two resistors on the relay board. Maybe they are way off in value. One thing about those on the 
relay board is that they do not have their own trough holes on one end. They are just soldered to the pads on the back with bent legs to make contact to GND. 

head phone resistors



Relay resistors: I need to measure these .




I will have to test this tonight, just to satisfy my curiosity if nothing else.

nashou

What do those driver board connectors look like. I wonder if you are getting bad connections in there. It seems like every time you remove and reinsert these boards you get different readings. These connectors remind me of the old Nintendo game consoles when I use to work on them. They were so problematic they had to be replaced with gold plated connectors. Can you snap a pic of the inside of these connectors?