SX-1250 Stabilizer - Pin 8 & 9 no volts

Title says most of it.

Stabilizer board 5.4 volt and 13.5 volt outputs are not outputting. I found that R17 is burned open. R18 is good. I don't want to just replace R17 - I assume something would cause this? I didn't find any dead shorts across any of the transistor or caps.

I am guessing that this is probably normal but the whole board around the Q3 Q4 area is very dark. There is evidence of previous meltdown around Q1 & Q2, but the +-65 volt supply seems good so I guess it was repaired.

Here are the readings of all the pins

1 -66
2 66
3 gnd

6 81
7 24
8 0
9 2.0
10 23

11 60
12 gnd
13 -65
14 -24
15 -83

What else would cause this?


My goal would be to make this machine bullet proof. My next question would be if this was likely caused by a problem outside the stabilizer board or is it normal for them to just quit?

I plan on replacing all the electrolytic caps. If I want this board to last another 30 years what else should I replace? If I knew suitable replacements, I would replace every transistor and diodes as well as the resistors that show heat damage.


Thanks!

SX1250 AWR106 power supply stabilizer assy

Something HEAVILY loaded down the 13v line - like a shorted cap - probably off board. C17 is the only thing that could short on that board to cause what you have seen. Replace r17 with exactly the same and for troubleshooting, use a 120 ohm 2 watt series resistor connected temporarily between pin 9 and it's wire to limit the current off board from doing it again until you find the short.
At 3.9 ohms and 1/2 watt, R17 would be at maximum heat capacity with 360mA (1/3 of an amp) flowing through it, thus the load should be lots less. With a short, and the 120 ohm resistor in place, the voltage on the load (not the pin 9 side) side of the 120 ohm resistor should be close to zero until the short is repaired.

Q9, Q10, Q11, D5 & D6 must be carefully checked for damage - or replaced outright...

--- --- --- +13v regulator --- --- ---

Q9: 2SD325R-E to-220 bce 35v 3a 10w 40-320hfe 8mhz Q9 pwr +13v pass
512-KSC2073TU_Q to-220 bce 150v 1.5a 25w 4mhz 40-140hfe $0.53

Q10: 2SC945A-R to-92 ecb 50v .1a .25w 50-600hfe 250mhz Q10 darlington dvr
512-KSC2310YBU to-92 ecb 150v .05a .8w 100mhz 40-240hfe $0.11 ea

Q11: 2SC945A-R to-92 ecb 50v .1a .25w 50-600hfe 250mhz q11 feedback
512-KSC1845UBU (ln)to-92 ecb 120v .05a .5w 100mhz 150-800hfe $0.05 ea

D5: WZ-061 6.1v 0.5w zener diode
512-1N5234B Fairchild 6.2V, 0.5W Zener

D6: 1s2473
512-1N4148 Diodes - Small Signal 100V Io/200mA BULK



Re: beefing things up, Q4 and Q8 come to mind... going from an itty bitty case to a larger case that can dissipate more heat.

*************
--- --- --- +25v regulator --- --- ---
Q4: 2SC1384-R to-92 ecb 50v 1a 1w 50-340hfe 200mhz Q4 +25v pos pass
512-KSC2682YSTU to-126 ecb 180v .1a 1.2/8w 200mhz 100-320hfe $0.31 ea

--- --- --- -25v regulator --- --- ---
Q8: 2SA684A-R to-92 ecb 50v 1a 1w 50-340hfe 200mhz Q8 -25v neg pass
512-KSA1142YSTU to-126 ecb 180v .1a 1.2/8w 200mhz 100-320hfe $0.28 ea
***********

********** the rest of these below are replacements IF needed, but I wouldn't fool with anything that's working. ********

--- --- --- +65v regulator --- --- ---

Q1: 2SD313P-E to-220 bce 60v 3a 30w 40-320hfe 5mhz Q1 pwr +65v pass
512-KSC2073TU_Q to-220 bce 150v 1.5a 25w 4mhz 40-140hfe $0.53

Q2: 2SC869-D to-92 bce 160v 30ma .2w 90hfe ?mhz Q2 darlington dvr
512-KSC2310YBU to-92 ecb 150v .05a .8w 100mhz 40-240hfe $0.11 ea

Q3: 2SC1318-R to-92 ecb 50v .5a .625w 85-340hfe 200mhz q3 feedback
512-KSC1845UBU (ln)to-92 ecb 120v .05a .5w 100mhz 150-800hfe $0.05 ea

D1: WZ-240 24v 0.5w zener diode
512-1N5252B Fairchild 24 V, 0.5W Zener

D2: 1s2473
512-1N4148 Diodes - Small Signal 100V Io/200mA BULK

--- --- --- -65v regulator --- --- ---

Q5: 2SB507P-E to-220 bce 60v 3a 30w 40-320hfe 5mhz Q5 pwr -65v pass
512-KSA940TU_Q to-220 bce 150v 1.5a 25w 4mhz 40-140hfe $0.54

Q6: 2SA628A-D to-92 ecb 25v .1a .15w 55-800hfe 100mhz q6 darlington dvr
512-KSA910YBU to-92 ecb 150v .05a .8w 100mhz 40-240hfe $0.12 ea

Q7: 2SA720-R to-92 ecb 50v .5a .625w 85-340hfe 200mhz q7 feedback
512-KSA992FBU (ln)to-92 ecb 120v .05a .5w 100mhz 150-800hfe $0.05 ea

D3: WZ-240 24v 0.5w zener diode
512-1N5252B Fairchild 24 V, 0.5W Zener

D4: 1s2473
512-1N4148 Diodes - Small Signal 100V Io/200mA BULK

--- --- --- 5.5v regulator --- --- ---

Q12: 2SD325R-E to-220 bce 35v 3a 10w 40-320hfe 8mhz Q12 pwr +5.5v pass
512-KSC2073TU_Q to-220 bce 150v 1.5a 25w 4mhz 40-140hfe $0.53

Q11: 2SC945A-R to-92 ecb 50v .1a .25w 50-600hfe 250mhz Q13 darlington dvr
512-KSC2310YBU to-92 ecb 150v .05a .8w 100mhz 40-240hfe $0.11 ea

Awesome - Thanks Mark, Parts ordered

I will update you in a few days if I got it working or not. I will fix the problem first, then once it's working I will refresh the rest.

BTW the 512-KSA910YBU are listed as obsolete, but fairchild lists the KSA910YSHTA as a direct replacement.

I'm still waiting for my parts to show up, but I figured I would start troubleshooting the external stuff so I wouldn't cook the supply once it is fixed.

I connected bench supplies to the 5.4 volt and 13 volt connections with the stabilizer board removed from the circuit.

All the lights on the 5.4v circuit seem to be fine, the AM light kind of flickers but I am sure that is a dirty AM switch.

The FM tuner works, and the stereo indicator works when tuned. I left it on FM overnight and it was still running this morning. I also verified that C17 on the stabilizer board is not shorted (right now). I don't have the 25v line hooked up to the tuner - but unless something cooked in the mute circuit I wouldn't think that would make a difference. The tuner is drawing about 100ma on the 13 volt line with the stereo light lit. The sound from the tuner sounds fine, and in stereo.


Is there something I should be looking for? A common intermittant part?

cbrworm said:

I'm still waiting for my parts to show up, but I figured I would start troubleshooting the external stuff so I wouldn't cook the supply once it is fixed.

I connected bench supplies to the 5.4 volt and 13 volt connections with the stabilizer board removed from the circuit.

All the lights on the 5.4v circuit seem to be fine, the AM light kind of flickers but I am sure that is a dirty AM switch.

The FM tuner works, and the stereo indicator works when tuned. I left it on FM overnight and it was still running this morning. I also verified that C17 on the stabilizer board is not shorted (right now). I don't have the 25v line hooked up to the tuner - but unless something cooked in the mute circuit I wouldn't think that would make a difference. The tuner is drawing about 100ma on the 13 volt line with the stereo light lit. The sound from the tuner sounds fine, and in stereo.


Is there something I should be looking for? A common intermittant part?

Click to expand...

Looks like you got it covered. Very well covered. This is the point where I put the repaired power supply board back in and don't expect fireworks.

(as long as where you fed the 13v into is the same wire as the power supply will and everything that will draw current off the power supply drew current from your substitute. i.e. nothing else intentionally disconnected)

Are you replacing C17? If not, I would test it at voltage solo off the board - something pulled enough current to destroy R17 and the transistor(s). I don't trust ohmmeters to be the final word about electrolyics that may have shorted - I check leakage at operating or rated voltage whenever possible - when I just don't replace them outright.

I am replacing C17 along with all the other electrolytics on the stabilizer board. I fed the 13v right into the wire at the connector that would normally plug into the board.

All the "gotcha's" are covered....

This has been an extraordinary thread - Just 6 posts and the problem is (will be) fixed.

OUTSTANDING.....

It is together and working. . . so far. I replaced all the caps on the stabilizer and protection board as well as fixing this problem. I wanted to make sure I could fix this before I broke the next thing.


Can you check something on Q6 for me? - it looks like its pinout is bce, but you have it and its replacement listed as ecb. I am probably transposing digits somewhere but I have looked at it multiple times and most of them it comes up bce.

As I move forward I am either going to replace or re-goop Q5 & Q1 (when I removed Q9 the heatsink goop had turned to dust). If I replace them I will do Q6 and Q2 which is why I am looking at them.


Thanks Again!

Well, I double checked the hi res 1250 manual (68 meg?) from the database.

Q6 is supposed to be a 2sa628a-d according to:
the schematic on page 78 of 94
the foil diagram on page 79 of 94
and
the parts list on page 80 of 94


On page 41 of 94 in the databases' .pdf file the 2sa628 has a layout of e c b with the flat of the transistor facing you, the leads pointing down and read from left to right.

I just visually confirmed that on my post #2, q6's listing is ecb and the ksa910 datasheet for the replacement shows ecb.

If you have been following other threads, the zetex ztx1056's references for lead layout may have confused the issue - every once in a while they trip me up because they're so different.

Perhaps on your board they didn't use a 2sa628, or it was replaced with something else?

No, I haven't been following the other threads.

My board definately has a 2sa628a (-d?)

looking at the face of the transistor with the legs pointing down, the pin farthest on the left (what I believe to be the base) is connected to the trace that leads to R4 and Q7. The middle pin is connected to the collector of Q5. The pin on the right is connected to the base of Q5.

I am not trying to be dense, please look at this picture and if you can figure out what I am doing wrong, let me know. I have no doubt that you are right, I just can't figure out how I could be misreading this.

And the +/- 65 volt circuit works and adjusts fine.

I SEE and appreciate your dilemma.

Our only source of info on the 2sa628 pinout seems to be the sx-1250 manual.

I have been working on a cross-reference database as to which transistors are used in which Receivers, and the 2sa628 appears to be used only in the 1250 of the x50 series (which is as far as I had gotten). No other manuals to check.

So with your picture, and the board's layout, you have to be right, that transistor's layout is BCE because the regulator is working.


edit: I have found a japanese datasheet, and found enough similarities in the kanj(?) characters from the translated specifications that I can infer the kanj only lead designations, and they appear to be Base, Collector & Emitter.

You are right, the 1250 service manual is confirmed wrong.

Which is why I always use a B & K transistor tester that identifies leads as well as testing functionality before I put in any transistor.

Since 99% of Japanese transistors have the collector as the center lead, finding the base is pretty easy...

markthefixer said:

I SEE and appreciate your dilemma.

Our only source of info on the 2sa628 pinout seems to be the sx-1250 manual.

I have been working on a cross-reference database as to which transistors are used in which Receivers, and the 2sa628 appears to be used only in the 1250 of the x50 series (which is as far as I had gotten). No other manuals to check.

So with your picture, and the board's layout, you have to be right, that transistor's layout is BCE because the regulator is working.


edit: I have found a japanese datasheet, and found enough similarities in the kanj(?) characters from the translated specifications that I can infer the kanj only lead designations, and they appear to be Base, Collector & Emitter.

You are right, the 1250 service manual is confirmed wrong.

Which is why I always use a B & K transistor tester that identifies leads as well as testing functionality before I put in any transistor.

Click to expand...

I got interested in the thread and just checked a source and all I could get was Japanese also but I'm in the dark as to translating it.
When I came back from checking you had posted the edit!!!!!!

Had me smiling.

Thank you very much for checking that. I check and double check everything and when I find something that doesn't match what's documented it makes me crazy - which is funny because in my industry people comlain that I don't document things well enough.

I also have the same service manual and kept going back and forth trying to figure out why my brain couldn't wrap around what I was seeing.

I don't yet have the confidence to rely on my findings without confirmation.

markthefixer said:

I SEE and appreciate your dilemma.

Our only source of info on the 2sa628 pinout seems to be the sx-1250 manual.

I have been working on a cross-reference database as to which transistors are used in which Receivers, and the 2sa628 appears to be used only in the 1250 of the x50 series (which is as far as I had gotten). No other manuals to check.

So with your picture, and the board's layout, you have to be right, that transistor's layout is BCE because the regulator is working.


edit: I have found a japanese datasheet, and found enough similarities in the kanj(?) characters from the translated specifications that I can infer the kanj only lead designations, and they appear to be Base, Collector & Emitter.

You are right, the 1250 service manual is confirmed wrong.

Which is why I always use a B & K transistor tester that identifies leads as well as testing functionality before I put in any transistor.

Click to expand...

Here's an INTERESTING update on the 2sa628 pinout situation...

something that slipped right by me!!!

The sx-1010 uses some 2sa628's !!!! and the sx-1010 service manual is WRONG TOO!!