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Trying to fix a universal 25-29 china chassis (SOLVED)
perjmolsen:
Hi Grant :)
You are right - it where my transformer that got the circuit breaker to trip when the game pcb where connected.
I have now used a isolation transformer and now the circuit breaker stays on, also with the game pcb connected to the chassis. :applaud:
I have tested the D1138 (NPN Power amplifier Vertical deflection) in my china tester and it tests OK.
I have changed the LA7840 (Vertical IC) to a new one, but I still have vertical collapse :cry:
What can else cause a vertical collapse?
perjmolsen:
An update more
I have tested that the LA7840 (vertical IC) gets voltages on pin 6
When I test i get 32V and according to the datasheet its from 16V to 33V so that is also OK.
Why do I have that vertical collapse.. it would be so nice if there where a schemetic for this chassis
perjmolsen:
An update more :applaud:
At some point I had removed a leg on all diodes... and forgot to solder one of them back in...
So put som solder on it and turned on the power, not longer a vertical collapse :applaud:
BUT I get picture but a small one, and after 20 sec the picture becomes unclear and i turn it off
I have noticed that the big 25W 140 ohms resistor gets really HOT, and when i cools down i can get picture again.
Is that because my yoke readings not are correct? Is it possible t add a resistor between blue and brown wire, so that i raise the vertical ohms? ex a 4 ohms resistor, so that my VR is beeing raised to 9.5 ohms?
VR: Blue - brown: 5.5 ohms
HR: Red - White: 1.7 ohms
And my chassis sticker says
VR: 9.6 ohm
HR: 1.3 ohm
perjmolsen:
If i measure the yoke with my china tester i get a slight higher ohms reading, I assume that is caused by my test wires.
VR: 6.8 ohms 10.83 mh
HR: 2.7 ohm 1.55 mh
The chassis sticker:
VR; 9.5 ohm VL: 24.6 mH
HR: 1.3 ohm HL: 1.5 mH
So my micro henry in the Horizontal is not in range... can I make it to be in range?
perjmolsen:
Update :)
I am able to dial in the picture like the one below, and also keep it there. I need to have the screen volt at the flyback turned nearly all the way down.
The b+ is set as low as possible at 110V but the big 140 ohm 25W resistor gets HOT HOT... I have read that a fix is to upgrade the resistor to an 150 ohm 100W and mount it at the chassis, I think that i will do that so that it does not set fire to anything
I think that my issue now is that the monitor not is suitable for the chassis, but now my chassis work :applaud:
So I guess that I have to look for another tube with other yoke readings :dunno