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Trying to fix a universal 25-29 china chassis (SOLVED)
perjmolsen:
I think that i will put this chassis to the side until I get a compatible monitor to test on.
perjmolsen:
Forgot to say - Thanks for all the help until now! :applaud:
:cheers:
GA61XX:
any luck with this monitor yet ?
this looks to be a cheaper version of the Wei-Ya 429 chassis, these are both very close to the Wei-Ya 825HR & Wei-Ya 826H schematics
These are a very versatile chassis with only changing a few components ;D
tube size selection is done via C909 0.01uf & C912 0.0047uf .. these are very wide & you may find the adjustments at the max
you can change C912 down to 0.0022uf to make dialling in a 29" easier.. & the 0.01 uf is best suited to a 27" tube.. about center of the H. Width potentiometer :)
So you now want to know what to use to suit any tube ?
C909 0.01uf & C912 0.0022uf will give best for 27" & 29" tube
C909 0.0082uf & C912 0.0022uf will give best for 25" & 27" tube
C909 0.0068uf & C912 0.0015uf will give best for 24" & 26" tube
C909 0.0068uf & C912 0.0022uf will give best for 23" & 25" tube
in short, you need about : 0.0072uf suit 23" , 0.0082uf suit 25" , 0.0104uf suit 27" & 0.0122uf suit 29"
Horizontal adjustment range is done via C908 0.33uf & C908A 0.1uf..
you then may need to change or trim C908 from it's 0.33uf.. so 0.47uf will give smaller picture & 0.22uf a larger picture, you want to aim for about center of the H. Width potentiometer :)
also trimming C912 either up or down from the values i gave above will a tighter tolerance on tube size..
P.S. i am yet to try these down to a 20" size tube.. but thinking C909 to 0.0047uf & C908 to 0.47uf will suit.. not sure.. but will up-date..
perjmolsen:
Hi
I have pulled out this china chassis again, because i am unable to locate the PSU fault at my Hantarex polo -> http://forum.arcadecontrols.com/index.php/topic,160193.msg1688348.html#lastPost
So I had hoped that my china chassis had worked as a temp replacement, but no.
I now have a A66 monitor that i can test my china chassis in, I got static on the screen, but no neck glow.
I have pulled one leg at all the big rised resistors at the chassis, all tests fine - I assume that they are safety resistors.
I have also checked all diodes at the chassis - all fine.
Put in a new LA7840 (vertical ic)
Tested the two BU2508 - all OK
How to I test my heater volts on this chassis?
GA61XX:
Ok.. heater voltage should be 6.3v AC
in the pic of your chassis from the top you have a white ribbon cable in the lower left corner
can not see in the pic is the "normally" 2.7 ohm 3W resistor .. as direct from China..
i normally change the to a 5.6 ohm 5W ceramic..
the 2.7 ohm will give about 9.7v ac on the heater.. where as the 5.6 ohm will pull it down closer to about 6.7v ac