SX-750 Voltage/Protection relay issues

[vmedia]

Thanks zebulon.
I'll make sure to match these components.
In the meantime, my question still stands on Q7/Q8 - unless I'm mistaken, 2SB527 are BCE? If that's the case, the previous transistors, and those in my other working unit, do not match the markings on the board. Knowing that I'm showing 31 volts at the right and left speaker outs from this board makes me wonder if this might be the problem? Just not sure how I should install the replacements...

 

[petehall347]

sorry late to the party .. all power supply voltages ok ?

 

[vmedia]

No worries - I let this sit for way too long and need to start at the beginning.
Under DBT and with NO output transistors connected:
Power supply:
1 - 28.4 vdc
2- 0
3 - 0
4 - 28.9 vdc
5 - 5.7 vac
6 - 5.7 vac
7 - 5.7 vac
8 - 28.5 vdc
9 - 28.9 vdc
10 - 28.5 vdc
11 - 29 vdc
12 - 0
13 - 0
14 - 0
15 - 4 vac
16 - 34.2 vdc
17 - 32.2 vdc
18 - 33.8 vdc
19 - 0
20 - 0

 

[petehall347]

1 - 28.4 vdc ????
will look at rest now to see .

 

[petehall347]

check 2 again

 

[petehall347]

this is awr-100 board ?

 

[vmedia]

Awr-099 board.
Yes - I know - this is the problem. FYI, I have disconnected the yellow wire between pin 1 and pin 36 on amp board.
Pin 2 measure 0 vdc

 

[vmedia]

Here's a pic of the power/protection board.

 

[petehall347]

cab you please use - only when negative voltage ?

 

[petehall347]

and include mv too . it is important .

 

[vmedia]

Sorry - One more time:
Note - none of the O readings measured any mv

1) -28.4 vdc
2) 0
3) 0
4) -28.9 vdc
5) 5.7 vac
6) 5.7 vac
7) 5.7 vac
8) -28.5 vdc
9) -28.9 vdc
10) -28.5 vdc
11) -29 vdc
12) 0
13) 0
14) 0
15) 4 vac
16) -34.2 vdc
17) -32.2 vdc
18) 33.8 vdc
19) 0
20) 0
21) 0
22) 12.7 vdc
23) 31.9
24) 31.9

 

[petehall347]

awr 100 voltages ?

 

[vmedia]

AWR-100

1) 5.8 vac
2) 4 vac
3) 0
4) 0
5) 23.4 vac
6) -29 vdc
7) 28.6 vdc
8) 23.4 vac
9) 0
10) 28.3 vac
11) 28.3 vac
12) 33.9 vdc
13) -34 vdc
14) 4.9 vdc
15) 5.6 vac

 

[Watthour]

You have -28V on Pin 1 of the AWR-099? That's bus voltage at the speaker (or nearly). The same condition applies to Pin 4 of the AWR-099.

 

[vmedia]

Understood - that's the problem I'm trying to fix. Any thoughts on next steps?

 

[zebulon1]

Pin one is the left channel and if you had the black probe grounded to the chassis, Q5 would be suspect as the center voltage is negative.

 

[vmedia]

Thanks. Q5 has just been replaced and I assume is still good.
I have checked voltages on Q5 and Q6.
Here are my findings (all vdc)
Q5
B -28.1
C -28.5
E -28.5

Q6
B -28
C +28
E -28

 

[vmedia]

Also checked Q3 and Q4 - 28 volts on each leg.
These are new transistors as well.

 

[Watthour]

No offense, but just asking... It there a half-pound of solder on each of those? Those seem to be completely shorted.

What replacement transistor(s) are you using for Q5/6?

 

[vmedia]

No offense taken. This is a strange problem and I'm as perplexed as you are. I got this unit in this condition and have been slowly bringing it back.
I've had both 2SC2383 and KSC1845 in Q5/Q6 - with the same issue. Currently KSC1845.
Attaching an image of the solder joints just to assure you that it's not solder bridges.