SX-950 In Protection ... maybe more issues SOLVED
- Thread starter Johnny_Law
- Start date
Ok this went from bad to worse with the accidental pin 13-14 bridge, since pin 14 carries -51.5V. I'm getting a burning smell from something on the power source when the unit is on (smells like it could be Q2) and the voltages at my transistors is telling some kind of a story. Everything is still kinda off, but Q2 and especially Q4 are way off.
I've also gone in and measured (most of) the resistors (in circuit fwiw). All of the 1/2 watt resistors are OK and right on the money. However, R15 is measuring 1.9ohms (not k, just ohms), and the following resistors each are measuring at half or below spec: R3, R8, R9, R12, R14, R16, R17, and R18.
I've also gone in and measured (most of) the resistors (in circuit fwiw). All of the 1/2 watt resistors are OK and right on the money. However, R15 is measuring 1.9ohms (not k, just ohms), and the following resistors each are measuring at half or below spec: R3, R8, R9, R12, R14, R16, R17, and R18.
petehall347
the brandy coffee man
r15 looks the winner .. q2 q4 shorted through .both b to c . b to e
i however dont understand why some of the others read wrong .. unless caps are charged are something .
ps zd12 might be pretty hot ..
i however dont understand why some of the others read wrong .. unless caps are charged are something .
ps zd12 might be pretty hot ..
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Yep so I'll order a bunch of replacements from Mouser tomorrow. I'm going to include many of the resistors and diodes as well. I'll hunt around for the appropriate replacements for the diodes - all of them.
Here are the bulk of my measurements tonight:
Resistors
Here are the bulk of my measurements tonight:
Resistors
Update. Been up to my elbows in the power supply all weekend, rebuilding, testing, pulling components and testing them, putting them back in, etc. I started by replacing all those bad transistors. I replaced all the diodes, including the zener diodes. I went to replace the resistors but realized that once out of circuit, they all measured correctly. So they all went back in. Lesson learned.
But unfortunately it's still in protection, and I am still getting really bad pin readings, except for pins 13-15. I have pulled and tested each transistor to confirm they are all actually operational. What does everyone think? I left the capacitors in place (silly of me), so I fear that at least C10 and C11 are open. Here's why: pins 13-15 are the only pins that aren't fed through a capacitor, and they're OK. Pins 6-11 come through Q1, Q3, Q5, and Q7 with C10 on the C side of Q1. And pins 2-5 are fed via Q8, Q9, and Q10 through C11.
Is there any way to test C10 and C11 out of circuit? My multimeter (Mastech MS8268) does test capacitance but only up to 20uF.
But unfortunately it's still in protection, and I am still getting really bad pin readings, except for pins 13-15. I have pulled and tested each transistor to confirm they are all actually operational. What does everyone think? I left the capacitors in place (silly of me), so I fear that at least C10 and C11 are open. Here's why: pins 13-15 are the only pins that aren't fed through a capacitor, and they're OK. Pins 6-11 come through Q1, Q3, Q5, and Q7 with C10 on the C side of Q1. And pins 2-5 are fed via Q8, Q9, and Q10 through C11.
Is there any way to test C10 and C11 out of circuit? My multimeter (Mastech MS8268) does test capacitance but only up to 20uF.
petehall347
the brandy coffee man
check voltage across zd11
and voltages each side of r1
need to get q1 working right before the other voltages come back up .
and voltages each side of r1
need to get q1 working right before the other voltages come back up .
zD11 has ~0V on both sides.
R1 is showing 67V on one side, and 36V on the other (closer to Q1)
So maybe C15 is suspect?
R1 is showing 67V on one side, and 36V on the other (closer to Q1)
So maybe C15 is suspect?
petehall347
the brandy coffee man
check zd11 for short circuit .
c15 might be bad ..hard to say .
c15 might be bad ..hard to say .
petehall347
the brandy coffee man
r2 is also dropping lots of voltage .
zd11 is to hold q3 base 14.6v above ground .if its shorted voltage drops to zero .
zd11 is to hold q3 base 14.6v above ground .if its shorted voltage drops to zero .
Well, right on again, zD11 (WZ-140) is shorted. I guess it's time to either order from Mouser again, or get an NTE5023A from my local shop this week. I did buy a bunch of NTE5022A (13V instead of 14V) from my local shop before - think it's worth putting in the 5022A for the time being?
R2 is good at 1.5k.
R2 is good at 1.5k.
petehall347
the brandy coffee man
13v so long as it is 13v when working should be fine for now at least .
Well it brought the pins much closer to correct. Still in protection. And the Protection pins to the relay look decent ... Now I'm really scratching my head.
petehall347
the brandy coffee man
need to see rest of protect voltages .
They seem pretty normal, other than pin 9 of course. And Q7 on the Protection board is good.
petehall347
the brandy coffee man
q7 voltages ?
I'll measure tonight - I tested it last night and it was a little slow at first, pretending to short very quickly, giving me a quick reading, before measuring open from B to C and B to E; it was quick to give me a reading the other way though, on both, so it's definitely not open.
Q7 reads 0V at both B and E, and 33.4V at C.
petehall347
the brandy coffee man
best look at q5 and q6 voltages next
Took a look. Ref values in parens.
Note, there's a discrepancy in the service manual for Q4 - the circuit diagram calls out -0.6V on E, but schematic shows it on C. I have the -0.6V on E and 16.4V on C.
So, B of Q6 isn't right, maybe R23 is suspect; B of Q5 is way off, maybe R18 is suspect? Both measured OK in circuit (R23 measuring 9K which is a little off).
I double checked all the diodes as well as R13 out of circuit and all is well.
Note, there's a discrepancy in the service manual for Q4 - the circuit diagram calls out -0.6V on E, but schematic shows it on C. I have the -0.6V on E and 16.4V on C.
So, B of Q6 isn't right, maybe R23 is suspect; B of Q5 is way off, maybe R18 is suspect? Both measured OK in circuit (R23 measuring 9K which is a little off).
I double checked all the diodes as well as R13 out of circuit and all is well.
