I recently picked up a SX 1050 that would power on but had no sound output. I am not getting the second relay to click. I opened it up and found the F1 and F2 fuses on 104 board were blown, replaced them and still would not work. Fuses are not blowing now but checked the voltages on the 103 board and found most were off. I replaced all the caps and most of the transistors on that board but still have issues with voltages at pins 13,15 and 16. Some of the others are off just a little. I suspect Q1 may be problem. Q1, Q9 and Q12 are only ones I did not replace. I did find a couple of the transistors were bad when I was replacing them. Was planning to go back in and replace the rest of these but thought it might be good idea to ask the guys here that have good working knowledge of these if there is something else I should be looking at.
SX 1050 power supply problems
- Thread starter JTF
- Start date
merlynski
Curmudgeon Electronicist
Welcome to AK 
Q1 is a suspect, as well as Q2 and Q9, or R1.
Test or replace those 3 transistors.
What is the voltage on AWR-103 at:
Pin 2* =
Pin 3=
Collector of Q1=
Positive side of C1=
Cathode of D1=
*If Pin 2 is not close to +76 vdc, check at AWR-104 pin 6. If pin 6 is not +76 vdc then (with power off) test D2, D3, D4 & D5 on AWR-104.
With power off measure R1, it should be 10 ohms. You may need to lift one end.
EDIT: more info
Q1 is a suspect, as well as Q2 and Q9, or R1.
Test or replace those 3 transistors.
What is the voltage on AWR-103 at:
Pin 2* =
Pin 3=
Collector of Q1=
Positive side of C1=
Cathode of D1=
*If Pin 2 is not close to +76 vdc, check at AWR-104 pin 6. If pin 6 is not +76 vdc then (with power off) test D2, D3, D4 & D5 on AWR-104.
With power off measure R1, it should be 10 ohms. You may need to lift one end.
EDIT: more info
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OK, first thing I tested was R1 and it is bad. Need to get 10 ohm resistor then I'll check more. I did check all the diodes on AWR 104 previously and they were all good.
Should I stay with 1W for R1? Metal film?
Should I replace the other resistors on the 103 board that look kind of heat discolored. They are not badly discolored just slightly.
Should I stay with 1W for R1? Metal film?
Should I replace the other resistors on the 103 board that look kind of heat discolored. They are not badly discolored just slightly.
merlynski
Curmudgeon Electronicist
For R1: It is listed in the Service Manual as 'Metal Oxide' which has better thermal ratings than Metal Film ( http://www.resistorguide.com/metal-oxide-film-resistor/ ). I would stick with Metal Oxide or wirewound. Do not go below 1 watt rating, higher is OK. If you cannot find a metal oxide or wirewound go with a higher wattage rated metal film (>/= 2 watts.)
Discolored resistors should be measured, replace if out of spec.
Did you test Q1, Q2, Q9?
I think you should stay with a one watt replacement(?) The 10 ohms is more of a fuse than anything. Raise it up from the board.
The circuit should be fine but the DBT will tell the story.
Note: Look at R19 its sister. Its a 2 watt? It is providing an additional -13v supply that R1 is not.
The circuit should be fine but the DBT will tell the story.
Note: Look at R19 its sister. Its a 2 watt? It is providing an additional -13v supply that R1 is not.
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merlynski
Curmudgeon Electronicist
Looks a bit toastyTook the sock off and it blew the outer layer off.
.Point well made! I was thinking of it primarily as 'ballast' to reduce the power dissipation of Q1. I learn new things every time I visit AK
.
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Replaced R1 and R19. Powered on and checked voltages on AWR-103 pins.
Pin 1 = 18.7
2 = 63.5
3 = -64.1
4 = 0
5 = 13
6 = 13
7 = -13.6
8 = -62.1
9 = -31.5
10 = -25.6
11 = -25.6
12 = ground
13 = 24.9
14 = 24.9
15 = 30.9
16 = 61.3
17 = 61.3
18 = 5.2
19 = 5.2
The DBT is slightly glowing so think there are more issues to deal with. I still do not hear 2 clicks of relays. Only hear the relay by surge resistor, clicks on after 1 second.
Measurements of transistors:
Q1 B= 62.1
C= 62.8
E= 61.5
Q2 B= 62.6
C= 62.8
E= 62.1
Q9 B= 13.7
C= 17.5
E= 13
Pin 1 = 18.7
2 = 63.5
3 = -64.1
4 = 0
5 = 13
6 = 13
7 = -13.6
8 = -62.1
9 = -31.5
10 = -25.6
11 = -25.6
12 = ground
13 = 24.9
14 = 24.9
15 = 30.9
16 = 61.3
17 = 61.3
18 = 5.2
19 = 5.2
The DBT is slightly glowing so think there are more issues to deal with. I still do not hear 2 clicks of relays. Only hear the relay by surge resistor, clicks on after 1 second.
Measurements of transistors:
Q1 B= 62.1
C= 62.8
E= 61.5
Q2 B= 62.6
C= 62.8
E= 62.1
Q9 B= 13.7
C= 17.5
E= 13
merlynski
Curmudgeon Electronicist
Voltages should be on the low side while on the DBT, and DBT glowing orange is probably OK. What wattage is the DBT bulb?
I would expect the voltage on AWR-103 pins 8, 9 and 10 to be lower (less negative) than their nominal voltages rather than higher as you list. Did you test/replace Q5, 6, 7, and 8?
Sounds like the soft-start circuit is working ok, a bit slow because of the DBT.
The protection circuit relay may not pull in while on DBT.
Make a quick DC offset voltage check of the power amp outputs, AWH-047 pins 4 and 17. Are they less than +/- 50 millivolts?
I would expect the voltage on AWR-103 pins 8, 9 and 10 to be lower (less negative) than their nominal voltages rather than higher as you list. Did you test/replace Q5, 6, 7, and 8?
Sounds like the soft-start circuit is working ok, a bit slow because of the DBT.
The protection circuit relay may not pull in while on DBT.
Make a quick DC offset voltage check of the power amp outputs, AWH-047 pins 4 and 17. Are they less than +/- 50 millivolts?
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I have a 150w lamp in the DBT. I replaced Q5,6,7 and 8. Measurement check on AWH-047 Pin 4= 2mv and Pin 17= 3.5mv. I have not touched the bias - offset pots yet.
Q5
B= -62.7v
C= -63.8
E= -62.1
Q6
B= -63.4
C= -63.8
E= -62.9
Q7
B= -14.1
C= -63.5
E= -13.7
Q8
B= -32.2
C= -45.2
E= -31.6
Thanks for all the help and quick responses from you guys, a wealth of knowledge here. Just wish I understood circuits and reading schematics better.
Q5
B= -62.7v
C= -63.8
E= -62.1
Q6
B= -63.4
C= -63.8
E= -62.9
Q7
B= -14.1
C= -63.5
E= -13.7
Q8
B= -32.2
C= -45.2
E= -31.6
Thanks for all the help and quick responses from you guys, a wealth of knowledge here. Just wish I understood circuits and reading schematics better.
