SX 1250 FM is dead

[Road king]

I do have 24 volts on pin 39 and 13 volts on pin 15 of AWE - 068

What do I check next

R

 

[Road king]

voltages on Tuner PCB pins

1=0v
2=0v
3=0v
4=10.1v
5=10.1v
6=0v
7=13.7v
8=5.06v
9=.54v
10=0v
11=0v
12=0v
13=5.06v
14=5.06v
15=13.7v
16=13.7v
17=0v
18=0v
29=0v
30,31,32 all = 13.7v
33=1.9v
34=6.7v
35=6.7v
36=0v
37=0v
38=5.06v
39=24.1v
40=0v
41= 0v
42=0v
44= ? should be signal from fm front end, how do I measure this?


No movement on either meter when walking the dial on fm. am works fine

skin test on 44 equals nothing, skin test on f4 produces music. not sure if its fm and moving the tuning dial does not change music , but both meters start working

Any help would be appreciated

Thanks

 

[zebulon1]

I’m just browsing the Pioneer threads and I’m not in the shop so my suggestions are only general in nature.
The tuner scat has the voltages listed for the tuner board.
Check all those voltages on the transistors and the FM IC’s. That will help narrow things down.
Higher voltages in the IF than expected on the emitters and collectors means there is on open in the signal path.
To low of voltage means a short. If the B+ is up to spec’s.
The IC’s pin voltages should be close to spec.
If it’s completely silent the IF could be dead. Double check all the B+ power feeds. There are a few. Some are hidden in the circuit.
When you select FM the circuit turns off the AM and turns on the FM. Make sure this circuit function works.

I didn’t check your voltage readings as I am relaxing with a beer. Tomorrow I will check into it more closely.

 

[Road king]

I’m just browsing the Pioneer threads and I’m not in the shop so my suggestions are only general in nature.
The tuner scat has the voltages listed for the tuner board.
Check all those voltages on the transistors and the FM IC’s. That will help narrow things down.
Higher voltages in the IF than expected on the emitters and collectors means there is on open in the signal path.
To low of voltage means a short. If the B+ is up to spec’s.
The IC’s pin voltages should be close to spec.
If it’s completely silent the IF could be dead. Double check all the B+ power feeds. There are a few. Some are hidden in the circuit.
When you select FM the circuit turns off the AM and turns on the FM. Make sure this circuit function works.

I didn’t check your voltage readings as I am relaxing with a beer. Tomorrow I will check into it more closely.

Thanks, I will check this stuff now, and report back

R

 

[Road king]

Thanks, I will check this stuff now, and report back

R

I’m just browsing the Pioneer threads and I’m not in the shop so my suggestions are only general in nature.
The tuner scat has the voltages listed for the tuner board.
Check all those voltages on the transistors and the FM IC’s. That will help narrow things down.
Higher voltages in the IF than expected on the emitters and collectors means there is on open in the signal path.
To low of voltage means a short. If the B+ is up to spec’s.
The IC’s pin voltages should be close to spec.
If it’s completely silent the IF could be dead. Double check all the B+ power feeds. There are a few. Some are hidden in the circuit.
When you select FM the circuit turns off the AM and turns on the FM. Make sure this circuit function works.

I didn’t check your voltage readings as I am relaxing with a beer. Tomorrow I will check into it more closely.

q1

pin
2=10.10mv
4=9.9mv
5=13.6v
7=13.6v

q2
pin
2=0v
4=0v
5=13.6v
7=0v

q3
pin
1=2.08v
2=2.05v
3=2.05v
7=6.7v
8=5.81v
9=5.81v
10=5.81v
12=5.3v
13=.6v


q4
pin
1=.14mv
2=.14mv
6=.15mv
7=.15mv

Pushing the fm push button turns off am and lights the fm indicator light

Multi path button has to be depressed to get static and music on skin test when touching f4

is there a way to verify I have IF coming out of front end? (local oscillator 10.7 hertz).

Thanks for the help

 

[zebulon1]

When tuning with the mutipath on, you hear sound. Can you tune any stations? Well, does the signal meter respond to tuning?
Is the 13 volts found on the VC board, Pin F?

Have you Deox and lube the controls yet? This step is important on this receiver.
That should be the first thing to do if it hasn't been done.

For kick's:
There's an FM DET out RCA jack on the back. Patch that into one of the AUX channels and see if you can hear the composite signal with the AUX selected.

 

[Road king]

When tuning with the mutipath on, you hear sound. Can you tune any stations? Well, does the signal meter respond to tuning?
Is the 13 volts found on the VC board, Pin F?

Have you Deox and lube the controls yet? This step is important on this receiver.
That should be the first thing to do if it hasn't been done.

For kick's:
There's an FM DET out RCA jack on the back. Patch that into one of the AUX channels and see if you can hear the composite signal with the AUX selected.

`With multi path on no sound and no action on meters, unless I touch F4 with finger then meters jump into action and I hear Spanish music. If I the try to tune the music stays the same.

I do have 13 volts on pin F on VC If you're talking about the gray wire that goes from pin 32 on tuner PCB to AWB 023. 13.6v ( I'm not sure if that's pin f)

Nothing when going jumping FM set out to aux

Controls are detoxed and I believe working as they should

 

[Watthour]

Just a couple more relatively easy possibilities - Has the FM De-Empahsis switch been cleaned and exercised? Are tests being done with the FM Muting off?

The FM Mute probably isn't a problem but the de-emphasiss might be. You're not getting anything out of the RF section, it would seem, and introducing some RF into the HA1197 apparently is enough to make noise through the rest of the IF, detector, and MPX stages.

 

[zebulon1]

Okay, I'm on board.
Sorry for the slow speed up.
I think you are inducing the signal through the dead IF into the HA1137.
There are voltage points in that IF chain. I see your readings on pins Q1 and Q2.
Your missing voltage on the pins 2(?). (Q1 and Q2).

 

[Road king]

Just a couple more relatively easy possibilities - Has the FM De-Empahsis switch been cleaned and exercised? Are tests being done with the FM Muting off?

The FM Mute probably isn't a problem but the de-emphasiss might be. You're not getting anything out of the RF section, it would seem, and introducing some RF into the HA1197 apparently is enough to make noise through the rest of the IF, detector, and MPX stages.

Muting function has been depressed and not depressed, makes no difference to test. Multi path when depressed produces music on skin test, nothing when not depressed

de-emphasis has been cleaned and exercised. I am in agreement rf might be dead. The thing is I don't know how to test to see if it is dead.

R

 

[Road king]

Okay, I'm on board.
Sorry for the slow speed up.
I think you are inducing the signal through the dead IF into the HA1137.
There are voltage points in that IF chain. I see your readings on pins Q1 and Q2.
Your missing voltage on the pins 2(?). (Q1 and Q2).

Yup should be 1.45 and 1.5 correct?

so does that me we are back to the front end?
IF so what next

R

 

[zebulon1]

I think your having to look closely at the Front end.
There's a few Mosfet's in the front.
I guess, see if they have voltage.
There should be a voltage better than the 10mV's on pin 44. Should be around 2v's?

 

[Road king]

I think your having to look closely at the Front end.
There's a few Mosfet's in the front.
I guess, see if they have voltage.
There should be a voltage better than the 10mV's on pin 44. Should be around 2v's?

I will check the voltages and report back

R

 

[zebulon1]

A couple of things to think about.
One or both of the IF amps HA1201 could be shorted. Hot to the touch? I'm going with the probability's at this point.
If no appreciable voltage is on pin 44 you may have to disconnect the pin (44) or remove Q1 and see if the voltage is back - getting closer to the 1.5v's it needs.
I'm throwing things out at this point.

Never forget about the good visual inspection!

 

[Watthour]

A DMM with at least 10MΩ/V input impedance would be safest for this. It may also be possible to use your favorite Spanish broadcast to inject signal at either of the bandpass cermaic filters to see what effects that has.

 

[Road king]

A DMM with at least 10MΩ/V input impedance would be safest for this. It may also be possible to use your favorite Spanish broadcast to inject signal at either of the bandpass cermaic filters to see what effects that has.

I do have a sencore sg 165

 

[Watthour]

That could be a help. Is there an o-scope available to monitor the SG165 output?

 

[Road king]

That could be a help. Is there an o-scope available to monitor the SG165 output?

yes

 

[Road king]

I will check the voltages and report back

R

see attached pic,

 

[Watthour]

Just for the sake of eliminating the question, is there around 2VDC on G2 of each of the FETs in the front end?

If we're lucky, the voltage is there and we can split the diagnosis in half by seeing if there is a 10.7 MHz elemental frequency at the drain of Q3, and then at Pin H .