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SX 1250 FM is dead

Watthour said:
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 .
Click to expand...
Please look at picture I just posted

Thanks
 
Road king said:
see attached pic,
Click to expand...

Is R1 intact? If open, that and the apparent low resistance at R2 could explain the high voltage at Q1. Also, in-circuit resistance may be lower if you are also reading the G/D leakage of Q1.


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Watthour said:
Is R1 intact? If open, that and the apparent low resistance at R2 could explain the high voltage at Q1. Also, in-circuit resistance may be lower if you are also reading the G/D leakage of Q1.


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Click to expand...
R 1 also measures 27k. I will lift a leg and measure both
 
Watthour said:
Is R1 intact? If open, that and the apparent low resistance at R2 could explain the high voltage at Q1. Also, in-circuit resistance may be lower if you are also reading the G/D leakage of Q1.


index.php
Click to expand...
What kind of solder is that, I don't seem to be able to melt it?

Do I just crank UP THE HEAT A GO FOR IT?

R
 
You can do it however you like, but it might be easier just to sit down to take the measurements. Sorry, I couldn't resist.
 
I've had "interesting" solder as well. It may help to use extra flux and add some fresh solder to mix the alloy into something more workable. I had an early 'Sui that had some really "special" solder like that. After adding fresh solder, the solder sucker had its way with it just like always.
 
With the voltage that was present before the resistor was replaced, there may be damage to those 3SK45s. They are rated at a maximum Vgs of 7.0V at either gate. The 13V you had there could not have done them a lot of good.
 
Watthour said:
With the voltage that was present before the resistor was replaced, there may be damage to those 3SK45s. They are rated at a maximum Vgs of 7.0V at either gate. The 13V you had there could not have done them a lot of good.
Click to expand...
Yup I have ordered replacement for Q1, Q2 and Q3. it will be about a week before I get them.

I don't really know how to check them

is there a way?

R
 
You could check resistance from each gate to source and drain. They should show practical infinity.
 
A DCA75 should be able to check it.
Test gate 1, then gate 2.
Maybe the DCA55 will too. :dunno:

I like Watthour’s check
 
I believe you'll need to pull it for use with the Peak tester, but it may not read anything meaningful if the gate(s) reads shorted. Mr. Atlas might not even be able to identify it as a component.
 
still waiting on parts, I was board so I pulled the suspected mosfet 3sk45

I tried to test it with mr atlas but it was not ID as a component

I tied the drain to both gates and measured that between source, I was expecting to get a reading of under 1k but instead got a open

I think that means its bad as suspected

Any thoughts. ?

Also I removed the output wire to board 44 and measured , results were .14 mv. not 1.45volts that was expected
 
Progress made, but I'm confused

Tonight I replaced Q1,Q2, and Q3 in the front end and Q1 and Q2 on the tuner board. Fm now works and plays music when multi path button is depressed, not when it's not. Cant get stereo light to come on either, Alignment will be in 2 weeks as I will be traveling for 10 days.

Here is my question. I should have about 1.45 volts at pin 44 on AWE-068. Tuner board. I have only .18mv. but I do have 1.45v at pin 2 of Q1 (HA1201). But not in-between R1 and F1. Is that the way is should be or could F1 be bad?

I have looked for those filters but have been unable to locate them, any ideas on where to find them?

Thoughts please

R
 
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