[Fixed] Sanwa 29E31, Dead Chasis after coulours diminished then gone...

[davidcoolman]

Merry Xmas Arcade enthousiasts!

i resurected a quite old 29E31s (according to dust accumulated on the PCB) by swapping the existing cliking Flyback with a previously known working one.
image was a bit blurry though compared to other similar chassis and focus wouldnt help.
after a few days of a varying ok to somewhat washed/dark image, image was gone complitely. no neck glow. HOT reads good.
I looked on the input transformer section and found that most voltages were 0v at secondary side (C831/833/834/835/836 that were changed for new ones)
I Checked Q801 and fond 0v at all pins execpt pin 1 (139v) and pin 5 vas varying from 10 to 15v.
My idea is to swap Q801 and do some testings on it
For next Xmas, i want a sanwa troubleshoot flowchard

 

[davidcoolman]

Dear All,
i swapped q801 with a "probably working" one and had a few voltages at chasis power supply secondary but under working specifications
TP1 (C831) 163.8v - 180v expected
TP2 (C833) 103v - 112v expected
TP3 (C834) 163.8v - 180v expected
TP4 (C835) 19.2v - 29v expected
TP5 (C836) 4.9v - 7v expected

HOT (q412) is good , I removed it and put a light bulb (220v -60W) between Collector and Emitter and no light at all
It seems it is doing voltage protection, any ideas ? thx

 

[davidcoolman]

Update:
Q412 was changed for a new, just in case.
D402 was good
R456 open
D401 was shorted on the right diode (between Q412 Col and D401 anode)

after changing D401 and R456, power-on instantly blew R456
Verdict:
something short in the horizontal deflection circuit

 

[davidcoolman]

Q412 was fried as well, using the bulb between colector and ground worked
Latest verdict: new fake HOT or short downstream

 

[davidcoolman]

Epilogue:
The HOT was legit so had to look else where
After checking all plastic and chemical capacitors, diodes and resistors, (even the mosfet Q404) around HOT in the hunt for the short, i found C416 being bad and c471 low.

i've also read that horizontal coil on the yoke, if shorted could fry a HOT but i dont have inductance meter (yet)
so i flipped a coin and decided not to wait for the meter and eventually kill another C5143
screen magnetized and image poped.
Definatley c416 was responsible for the short

As a note, i changed Flyback with an HR compatible with a 68k resistor mod but had to turn screen way up to have RGB pattern displayed correctly so definatley something is still low.
not having a HV probe, i cant tell if i have the expected 27kV so my only option to guess if chassis stays ok is to play loads of games