Trying to fix a universal 25-29 china chassis (SOLVED)

[perjmolsen]

Hi 

It is exiting to learn something new/more  And while waiting for parts to my other repair I will try to learn

I got this 25"-29" unknown brand china chassis for free.
I want to see if I am able to fix it. If i can - maybe someone can use my information 

Yoke data:
VR: 9.6 ohm VL: 24.6mH
HR: 1.3 ohm VL: 1.5mH

The fault where that it where dead.

So far I have found the following faults:
Both BU2508 where shorted - also one of the two 3A 250V fuses where blown.

I have changed the two BU2508  and also the fuse.
Tested the D1138 out of circuit, its tests OK. http://pdf.datasheetcatalog.com/datasheet/HitachiSemiconductor/mXwuvvr.pdf

When i turn it on now, it seems that there is static, and the fuse does not blow, neither the BU2508 blows.
But the D1138 gets verry hot

If I follow the pcb trace from D1138 it get to the Vertical IC LA7840
With my limited skills then I think that i might be the LA7840 who causes the D1138 to get very hot

So i have orderd som new LA7840 in china

My rep log: https://www.dropbox.com/s/b2gtaciyxx86jfu/25-28%20inch%20china%20chassis%20rep%20log.xlsx?dl=0

[princess prin prin]

Given the lack of schematics a shot of the underside would help.

[perjmolsen]

Some pictures of the chassis
Nearly in the middle of the picture there is three holes, its there that D1138 where mounted (the component that gets hot when the chassis is turned on)

[princess prin prin]

If I follow the pcb trace from D1138 it get to the Vertical IC LA7840
With my limited skills then I think that i might be the LA7840 who causes the D1138 to get very hot

I disagree. The trace you followed is not relevant as it's ground (the emitter of the transistor is ground and so is one of the pins of the vertical IC). The transistor is likely to be the pincushion correction output transistor. Its collector goes through that big black coil (the bridge coil) to the line output/horizontal deflection circuit, more specifically to the anode of a diode and the cathode of another diode, i.e. the usual damper+modulator diodes that are found in all chassis with pincushion correction.

You first need to check if you have the B+ voltage that goes to pin 2 of the flyback. Lift one side of the 33K resistor to the right of the yoke headers so the horizontal drive transformer (yellow one) is not powered and isolate pin 2 of the flyback and connect a light bulb to it and see if it lights up and how much voltage you have. You need an isolation transformer for this chassis.

[perjmolsen]

You first need to check if you have the B+ voltage that goes to pin 2 of the flyback. Lift one side of the 33K resistor to the right of the yoke headers so the horizontal drive transformer (yellow one) is not powered and isolate pin 2 of the flyback and connect a light bulb to it and see if it lights up and how much voltage you have. You need an isolation transformer for this chassis.
[/quote]

Hi

Well I think that you are right  (you always has.. so)

But you say the 33K resistor next to the yoke header...
I see the following.. (if my eyes see colors correct.. they not always do)

680 ohm (blue- gray-brown-gold)
2.6 ohm (red-blue-red-gold)
3.3 ohm (orange-orange-red-gold)
0,75 ohm (violet-green-silver-gold)
1 ohm (brown-black-gold-gold)
6,8k ohm (blue-gray-red-gold)
380 ohm (orange-gray-brown-gold)
1 ohm (brown-black-red-gold)

And pin 3 of flyback is this one right? ( i will isolate that, and put a 40W light to the other pad, and ground to heatsnik)

I have an 110V isolation transformer - and correct me, I do NOT need to hook the chassis up to a monitor to test the volt (when i have removed the resistor and isolated pin3 of flyback?)
Its easier to test it at the table..

[princess prin prin]

The big 3.3K resistor (orange/orange/red).

And pin 2 of the flyback, not 3 and of course the lightbulb needs to be connected to the trace not to the pin itself. Or desolder the HOT and connect the bulb to the middle pad (in this case you don't have to lift the resistor).

Is that isolated or an autotransformer?

[PL1]

The "Pin3 flyback" photo above appears to show a tiny glob of solder shorting the pin 4 and pin 9 traces below pin 4 and some residue on/near several solder joints that looks like flux.

It would be a good idea to clean those areas with some isopropyl alcohol and a Q-tip.   


Scott

[grantspain]

i would like to add that the flybacks used on these chinese clone chassis are pretty rubbish, i had a weiya clone less than a year old come in for repair with flyback bad- cheaper to buy a replacement chassis

[perjmolsen]

The big 3.3K resistor (orange/orange/red).

And pin 2 of the flyback, not 3 and of course the lightbulb needs to be connected to the trace not to the pin itself. Or desolder the HOT and connect the bulb to the middle pad (in this case you don't have to lift the resistor).

Is that isolated or an autotransformer?

Hi

Oh yes pin 2 a typo and a drawing error from my side.
I have removed the one leg of the big 3.3K resistor
One wire from the 40W bulb to pad of pin2

And i have 115.4V at the pad - I assume that is good
Note that the D1138 is not put in yet.

About the transformer, i do not know if that is an isolated or autotransformer... it only says step up or down transformer and it gives 110V at one outlet and 220V at another.
Any conserns?

What to test next? I assume some low volts ex at LA7840 at pin 6 - datasheet says recommended 24V

Another thing...
The best monitor for this chassis - I guess that i should be one as close to the vertical and horizontal ohms reading.
Chassis:
VR: 9.6 ohm VL: 24.6mH
HR: 1.3 ohm VL: 1.5mH

I got a monitor with this reading
VR: 12.9 ohm (yellow -green)
HR: 2.1 ohm (red-blue)

I guess that is to high - for best compatibility is is best to be under og over?

Thanks again 

[perjmolsen]

The "Pin3 flyback" photo above appears to show a tiny glob of solder shorting the pin 4 and pin 9 traces below pin 4 and some residue on/near several solder joints that looks like flux.

It would be a good idea to clean those areas with some isopropyl alcohol and a Q-tip.   


Scott

Hi Scott

Thanks for the notice
I have now removed it 

[perjmolsen]

i would like to add that the flybacks used on these chinese clone chassis are pretty rubbish, i had a weiya clone less than a year old come in for repair with flyback bad- cheaper to buy a replacement chassis

Hi

Yes I do not either have any hopes for this repair - it is just trying to learn, and get some "universal" fault finding tips from you great guys, and kill the time waiting for my last parts to my Nano MS9-29SU repair for my scud race.

I have order the last caps in UK - i do not want to wait any longer for china 

[princess prin prin]

Another thing...
The best monitor for this chassis - I guess that i should be one as close to the vertical and horizontal ohms reading.
Chassis:
VR: 9.6 ohm VL: 24.6mH
HR: 1.3 ohm VL: 1.5mH

I got a monitor with this reading
VR: 12.9 ohm (yellow -gold)
HR: 2.1 ohm (red-blue)

The values on the chassis label are for a common yoke type used for 25"-28" TV tubes. A Hantarex Polo has a tube with those readings.

What tube (type number) are you using?

[perjmolsen]

Another thing...
The best monitor for this chassis - I guess that i should be one as close to the vertical and horizontal ohms reading.
Chassis:
VR: 9.6 ohm VL: 24.6mH
HR: 1.3 ohm VL: 1.5mH

I got a monitor with this reading
VR: 12.9 ohm (yellow -gold)
HR: 2.1 ohm (red-blue)

The values on the chassis label are for a common yoke type used for 25"-28" TV tubes. A Hantarex Polo has a tube with those readings.

What tube (type number) are you using?

Hi

I have found an old TV and pulled it apart, to see if i could use it for testing chassis, it has the same pins at the neck, but only a 20"
I guess that i need to find a 25-29 inch real arcade monitor to use for test.
I did not want to use one of my working arcade monitors if i break something

[princess prin prin]

Yeah, you need an A59 or A66 tube. It doesn't have to be from an arcade monitor.

[perjmolsen]

Yeah, you need an A59 or A66 tube. It doesn't have to be from an arcade monitor.

OK Thanks

I had another old TV - pulled it apart
It had also the correct neck pins but still high reading, but a bit lower..
Tube A48 i guess..

VR: 11.2 ohm
HR: 1.9 ohm

[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! 
 

[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   
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

[perjmolsen]

Hi

Thanks for your help.
I have tested the resistors behind the ribbon cable they are fine.

If I try to measure volts at the resistors, and the chassis as ground I have 0 volts.
My fuses are good, also my two BU2508  is good.

I have to figure out what delivers my heater volts, do you have a schematics that are close to my chassis?

[princess prin prin]

Heater is most likely from the flyback. Just follow the trace from pin 9 or 10 of the CRT socket back to the main chassis and you'll see where it goes.

[perjmolsen]

Hi

I have now found a A59 tube  it is from a  Panasonic 25" inch TV
When i do the yoke readings i get the following

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

The vertial is a bit lower on the monitor, and the horizontal is a bit higer but do you think that would be OK? it is a A59 tube.

So would it be worth a try to connect the china chassis to the tube and see if I get any luck with neck glow and maybe picture on the screen 

[perjmolsen]

Hi

An update

I have now connected the chassis to the monitor, when I turn it on i got a vertical collapse, so it seems that the chassis works with the crt

BUT something stange is also - when I connect the input from the game pcb to the chassis, and turn it on the circuit breaker in my room triggers.....??!

I will try to change the D1138 (NPN Power amplifier Vertical deflection) newer changed, I had previously order sone new but newer received them, so I have order some new today
and also the LA7840 (Vertical IC) again, to see if that fixes the issue.

[grantspain]

needs to run on an iso transformer

the vertical impedance is very low for a cga chassis but it should sort of work

[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. 

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

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 

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 

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 
So I guess that I have to look for another tube with other yoke readings

[grantspain]

polo 2 auto with 12r resistor at r35 would match that tube better

[perjmolsen]

polo 2 auto with 12r resistor at r35 would match that tube better

Thanks  I think that I have a Polo 2 auto chassis somewhere  

[princess prin prin]

You can also use a Polo chassis with the components in the right column:

[perjmolsen]

You can also use a Polo chassis with the components in the right column:

Thanks - super with all your help