Problrms with Pioneer SX-780 source.

I wanted the emitter, and your markup shows 9.4V there.

Something is wrong in the 13.5V supply, either with something overloading the supply or a fault with the 14V zener diode (D4). Try measuring that voltage with the unit in each of its operating modes, including AM, FM, phono, and AUX.
 
I wanted the emitter, and your markup shows 9.4V there.

Something is wrong in the 13.5V supply, either with something overloading the supply or a fault with the 14V zener diode (D4). Try measuring that voltage with the unit in each of its operating modes, including AM, FM, phono, and AUX.


(sudenly sounds relay's click and source led iluminates brigther but Voltage rises to 10VCD in Q25 collector and back to low voltage then rises to 13.9VCD, and back to low Voltage)

Q25 Collector Voltage
NORMAL MODE -------------------- MONITOR MODE
AM= 39.8 VCD ------------------------- AM= 40.0 VCD
FM= 40.0 VCD --------------------------- FM= 40.3 VCD
Phono= 39.8 VCD --------------------------- Phono= 40.0 VCD
Aux= 39.8 VCD --------------------------- Aux= 40.0 VCD


Q25 emiter Voltage
NORMAL MODE -------------------- MONITOR MODE
AM= 9.0 VCD ------------------------- AM= 9.4 VCD
FM= 9.4 VCD --------------------------- FM= 9.8 VCD
Phono= 9.0 VCD --------------------------- Phono= 9.4 VCD
Aux= 9.0 VCD --------------------------- Aux= 9.4 VCD


D4 Voltage (same node as Q25 base)
NORMAL MODE -------------------- MONITOR MODE
AM= 9.3 VCD ------------------------- AM= 9.6 VCD
FM= 9.7 VCD ---------------------------- FM= 10.2 VCD
Phono= 9.3 VCD ------------------------ Phono= 9.6 VCD
Aux= 9.3 VCD -------------------------- Aux= 9.6 VCD
 
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q25 emitter voltage might be more revealing .. i do suspect the 14v zener ..but maybe not .

Unsodied D4 (zenner diode) and measured resistance values:

scale 2M reads 0.686
scale 200k reads 98.2
scale 20k doesn't reads
scale 2k reads 0.814
scale 200 doesn't reads

I INVERTED OHMMETER LEADS
scale 2M doesn't reads
scale 200k doesn't reads
scale 20k doesnt reads
scale 2k doesn't reads
scale 200 doesn't reads

Is right to read different values on different scales?

Plugged to 19 Volts VCD sourge and a serial resistence it reads 14 VCD and inverted leads of zener reads 1 VCD.

Installed back D4 zener diode on stereo receiver and reads 8 VCD
 
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It sounds like the zener is operating properly according to your voltage test.

It may be good to investigate the circuit around Q19 and Q21 due to the low voltage in that area, including C311, D3, and surrounding components. The 14V reference may be pulled low by something in that area.
 
Today I was trying to find my problem with variable Voltage and took like and hour or two to start to fail Voltages. Then Voltage problems start to clicks protection relay.

After that I was thinking in R1.
In R1 should read right values: 53.5 VCD before R1 and 25.9 VCD after R1, so difference in R1 should be 27.6 VCD;
But I rode 54.5 VCD before R1, 39 VCD after R1 and both leads of R1 15.4 VCD

Then I calculated R1 Voltage error:

(27.6 VCD - 15.4 VCD) / 27.6VCD = 0.4420

So I thought there is a 44.2% of Voltage in R1 that is not correct.

R1 is working wrong in load working condition 220 Ohms * 0.4420 = 97.24 Ohms less of difference compared with nominal value, so I think R1 is working with 122 Ohms with the unit turned on.

I turned off main power switch and quickly measured resistence and found out innestable resistence in R1, reading from 130 Ohms, 140 Ohms, 150 Ohms, 10 by 10 Ohms in every second....... and after some seconds R1 got stability on 210 Ohms.

I don't know if those rolled up wires on R1 are the problem, but I'm sure that the problem is on R1, now I see R1 just as a Voltage reduction in serial connection with the other part of the system. So my bet is on R1. Just gonna look for a 220 Ohms 5W resistence, maybe on ebay.

Thank you.
 
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Hello, I changed R1 but Voltage innestability problem stills remains ;(

Then transistors tester arrived to home and took apart and tried Q25, Q19 and Q20.

Looks like my problem is on Q25, tester looked it like a diode.

Now I just changed Q25 and looks like problem is solved.
 
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I just recaped whole caps, I used elna and nichicon caps, includes FM section. Definetly whole performance is much better, including FM section. I added a heatsink on Q25.

The bigger caps are 8000uf but I just found 8200uf, I don't know if something's wrong with my cap tester but in both of values no one gave the exact capacitance value, I don't remember but old elna read like 7000uf or 6800uf and news reads like 7500uf.
Maybe needs to replace whole transistors too but,I just recapped and sounds awesome.
 

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Hello, I changed R1 but Voltage innestability problem stills remains ;(

Then transistors tester arrived to home and took apart and tried Q25, Q19 and Q20.

Looks like my problem is on Q25, tester looked it like a diode.

Now I just changed Q25 and looks like problem is solved.
 

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