I will try that, I do have new KSC in stock,, the SX-680 does not have a pot in the LO for adjustment.
Speaking of pilot, I put a frequency meter on the correspondent pin of the IC to check for that and it is present (sawtooth) unstill you vary the voltage. If you go too high that it disappears.
Speaking of pilot, I put a frequency meter on the correspondent pin of the IC to check for that and it is present (sawtooth) unstill you vary the voltage. If you go too high that it disappears.
You may have some sort of parasitic oscillation that is causing RF interference at full voltage coming off of one ot the amplifiers.
If you are using an incadescent bulb in the ac line to limit power you can use a 25, 60 and 100w bulb if you have any. I used a 60w and 100w when testing the mosfet amp that went in the 780.
There is a 6.8uf tantalum cap in they that can be replaced by a 4.7uf electrolytic. If it is leaky it could be the problem.
If you are using an incadescent bulb in the ac line to limit power you can use a 25, 60 and 100w bulb if you have any. I used a 60w and 100w when testing the mosfet amp that went in the 780.
There is a 6.8uf tantalum cap in they that can be replaced by a 4.7uf electrolytic. If it is leaky it could be the problem.
I am using a variac to reduce VAC (60 Volts) not a dim bulb tester.
I am aware of suspicious tantalum & solid aluminum capacitors that Pioneer used during that era, I will look at that again, but most of the capacitors have been replaced (electrolytic) and other ones involved around the two PA ic's swapped for testing purposes without significant results. My next targets will be the LO & IF amplifier transistors, I would rather not mess too much with the front FM board, but sometimes you have to do............
I ordered a TinySA that will help me analyzing the signals, thanks
I am aware of suspicious tantalum & solid aluminum capacitors that Pioneer used during that era, I will look at that again, but most of the capacitors have been replaced (electrolytic) and other ones involved around the two PA ic's swapped for testing purposes without significant results. My next targets will be the LO & IF amplifier transistors, I would rather not mess too much with the front FM board, but sometimes you have to do............
I ordered a TinySA that will help me analyzing the signals, thanks
A variac is the perfect tool. Tune It in at 60v when it is clear and slowly move up till is craps out then scope the IF and repeat moving on stage by stage to locate the problem.
The more I dig the more I find. On the collector of Q505 & Q506 I am measuring 7.5 V, something could be wrong with the muting circuit & throwing everything off. For the PA3001A in order to work properly & pass the signal (stereo) the voltage will need to be about 0.2 V on pin 5 & 12. If that value floats around 4.5 to 5 Volts (like in my case) the signal will be forced to mono.
Wow brother we are that close from take off......grounding pin 5 & 12 of PA3001A with a 220 ohm resistor stabilize the circuit FM & the signal is perfect & I am seeing the stereo LED (flickering) on after a long time, this is not on all the time but I am very satisfied up to this point. I must thank you for being around.