Pioneer SX-1280 voltages at power supply and no FM

[xalara76]

Unit is working under AM, tape, phono, aux, but I am not getting any meter movement or signal under FM. I measured at Power supply pin 16 Orange wire and I am not getting the 13 V, checked back to the power supply and receiving 0 V. This unit has been recapped, and we also replaced the diodes / transistors on protection board / power supply.

There was a fault where one of the metal backed transistors on the power supply touched the main metal diode on the protection circuit at one point and created a small spark.

Where to check now ? Problem is obviously within power supply since it’s showing 0 volts.

 

[mrk229]

checked back to the power supply and receiving 0 V.

Checked back where, where did you get zero volts? We can't help you without good information to work from.

What transistor touched what? Transistor Q#X, a picture anything to help us know.

Are the dial lights on? If yes then the fuse (FU2 2 amps) for that section of the power supply is good? If you have no dial lights the fuse is probably blown

if the fuse is good then we will move ahead to check voltages at a couple of spots.

Check both sides of R15 for voltage, looks like it should be in the 20 volt range.

If both sides have voltage then move on to the base of Q5 and check there.

 

[mrk229]

That 13 volt supply runs the meter circuits, the source lamps, the tuner board and the protection board.

You say AM tape phono and aux are working. That implies that the protection circuit is working, which is contradictory to having no voltage at pin 16.

Pins 16, 17 and 18 should all have + 13 vdc on them.

 

[xalara76]

That 13 volt supply runs the meter circuits, the source lamps, the tuner board and the protection board.

You say AM tape phono and aux are working. That implies that the protection circuit is working, which is contradictory to having no voltage at pin 16.

Pins 16, 17 and 18 should all have + 13 vdc on them.

OK, just rechecked pins 16, 17 and 18 have 13.2 VDC on them. I had left my meter on diode test mode that’s why I was getting 0 V at the initial reading. (I need to remind myself to not work past 8pm on this stuff) lol.

So we know that the power supply is working. I guess this means back to the FM board. Traced the orange wire back to the FM board and it delivers 13.2vdc there as well so no breaks in circuit. Something’s not turning on for the fm modulator or there’s bad chips ? d6 on protection board touched a metal backed transistor on the power supply after that even when the unit was off and it did a little spark. Not sure if that caused anything ?

Triple checked all the caps I did. How to test IC’s ? Possible bad resistors ? I don’t see anything burnt.

 

[mrk229]

OK, just rechecked pins 16, 17 and 18 have 13.2 VDC on them. I had left my meter on diode test mode that’s why I was getting 0 V at the initial reading. (I need to remind myself to not work past 8pm on this stuff) lol.

Been there done that.

Did you recap the tuner board? There are two 13 volt supply wires coming to that board. Pin 30 and pin 11 of the tuner board should have +13vdc.

Check each IC for excessive heat with your finger.

Is this the same 1280 you posted about before? https://audiokarma.org/forums/index...-am-dead-fm-no-tuning-meter-movement.1095396/

 

[xalara76]

Just checked pin 30 and I’m also getting the 13.2 VDC. IC’s are not hot. I do notice a weird fault however with the “stereo” lamp. From my experience that Stereo lamp is only supposed to come on during FM, but it comes on when I press a.m. and then sometimes stays on under other functions as well but never on FM. Not sure if this is linked or useful information.

 

[mrk229]

Just checked pin 30 and I’m also getting the 13.2 VDC. IC’s are not hot. I do notice a weird fault however with the “stereo” lamp. From my experience that Stereo lamp is only supposed to come on during FM, but it comes on when I press a.m. and then sometimes stays on under other functions as well but never on FM. Not sure if this is linked or useful information.

Yep should only come on when receiving stereo. Has the bulb been changed to LED?

Again...Is this the same 1280 you posted about before? https://audiokarma.org/forums/index...-am-dead-fm-no-tuning-meter-movement.1095396/

And again did you recap the tuner board?

Either way the troubleshooting steps to confirm power at the chips is the same. See the other thread for power tracing to each section.

 

[xalara76]

Yep should only come on when receiving stereo. Has the bulb been changed to LED? Again...Is this the same 1280 you posted about before? https://audiokarma.org/forums/index...-am-dead-fm-no-tuning-meter-movement.1095396/ And again did you recap the tuner board? Either way the troubleshooting steps to confirm power at the chips is the same. See the other thread for power tracing to each section.

 

[xalara76]

Bulbs are all original. This is a different unit but poses similar issues - (it’s been hacked up really bad in its past life) - tuning boards have been recapped, I checked over orientation 3x. All correct. If I messed up values I’d be blown away. I checked over those 5x + and replaced 1 by 1.

 

[xalara76]

Bulbs are all original. This is a different unit but poses similar issues - (it’s been hacked up really bad in its past life) - tuning boards have been recapped, I checked over orientation 3x. All correct. If I messed up values I’d be blown away. I checked over those 5x + and replaced 1 by 1.

Yep should only come on when receiving stereo. Has the bulb been changed to LED?

Again...Is this the same 1280 you posted about before? https://audiokarma.org/forums/index...-am-dead-fm-no-tuning-meter-movement.1095396/

And again did you recap the tuner board?

Either way the troubleshooting steps to confirm power at the chips is the same. See the other thread for power tracing to each section

Yep should only come on when receiving stereo. Has the bulb been changed to LED?

Again...Is this the same 1280 you posted about before? https://audiokarma.org/forums/index...-am-dead-fm-no-tuning-meter-movement.1095396/

And again did you recap the tuner board?

Either way the troubleshooting steps to confirm power at the chips is the same. See the other thread for power tracing to each section.

Have a multimeter with this. Will check those resistors mentioned if I can make out the horrible scans of the service manual. lol

 

[xalara76]

Yep should only come on when receiving stereo. Has the bulb been changed to LED?

Again...Is this the same 1280 you posted about before? https://audiokarma.org/forums/index...-am-dead-fm-no-tuning-meter-movement.1095396/

And again did you recap the tuner board?

Either way the troubleshooting steps to confirm power at the chips is the same. See the other thread for power tracing to each section.

I just got back, touched the ICs and none of them are getting hot, is there a photo that you can provide on where those resistors are that I need to test with the multimeter?. Please circle them for me. I’d really appreciate it.

 

[mrk229]

The SX-1080 uses the same tuner board. My manual for that is much clearer. I have attached the tuner schematic and Board layout. See if that helps you fins the parts.

Damn forgot AK resizes them, won't be much help. You may already have a 1080 manual, if not grab it.

 

[xalara76]

The SX-1080 uses the same tuner board. My manual for that is much clearer. I have attached the tuner schematic and Board layout. See if that helps you fins the parts.

Damn forgot AK resizes them, won't be much help. You may already have a 1080 manual, if not grab it.

Appreciate that ! Got them zoomed in and checked.. everything matches the ohms in the service manual ! Which is good, but also bad cause we still don’t know where the problem lies .. but getting closer !

 

[xalara76]

The SX-1080 uses the same tuner board. My manual for that is much clearer. I have attached the tuner schematic and Board layout. See if that helps you fins the parts.

Damn forgot AK resizes them, won't be much help. You may already have a 1080 manual, if not grab it.

At this point, I guess I should test the ICs or should I look at the caps and compare them to the schematic for voltages / ratings ?

 

[mrk229]

At this point, I guess I should test the ICs or should I look at the caps and compare them to the schematic for voltages / ratings ?

In that other thread I noted some of the IC pins for power or you can figure it out from the schematic/pc layout.

You may wan to go and confirm you have voltage at the IC itself.

I avoid that if I can since it is so easy to slip and short to another pin. It always happens when I look away to see the meter .

The meters not moving points to a lack of signal or a total loss of signal most likely in the IF section.

The meters are both driven off of this IC (Q5), and the only active device in the IF strip is Q4. You may want to confirm the voltages in that area.

 

[mrk229]

It is possible the tuner section is not working. The signal from it comes into the previous post picture at R15 next to F1. To go much further you pretty much need a scope to see if the signal is present or not.