Aero / Nanao missing colors

[JaguarWong]

Hi,

So I bought an Aero City with a wonky monitor, right. Green was missing.
I get home, hook it up -> Green's back... But red's gone =(

Turns out the green was a cold solder (which I fixed cause it was still
acting up once in a while). Unfortunately the red wasn't that easy to
fix. So I swapped red and blue on the neckboard to check if the tube
was still able to display red after transferring the cab.
That worked. All blue was now red. So I focused my attention on the
pots. Measured the working pots, compared the results to the red pot.
Looks like that checks out. So this is pretty where my skill set ends =(
Does anyone have any tips for where I should look next ?

The facts:
- Chassis: Nanao MS8-26A / SU 15-25K
- Looks like the problem is in the main board
- Doesn't look like it's cold solder (did the tapping thing)
- Doesn't look like it's the pots (multimetered them)

Any leads on how to continue diagnosing would be much appreciated.

Please be gentle though. I know my way around a soldering iron and
Multimeter, but I'm pretty new to monitor repair. So easy on the
jargon please =)
Also, I'm not a native English speaker so excuse all the grammatical
errors and stuff... Thanks !

[ElPancho]

Hope you get this sorted Dave.
Can't be of help atm, you've tried more than I would have thought of.
But if you want anything checked on another (my) Aero or chassis just give a me a shout.

[grantspain]

sounds like the drive transistor is shorted,there are three colour drive transistors on the neck card-you can prove it if you swap the red and blue transistors over

[JaguarWong]

Thanks guys for the quick replies !

I'm goanne check if those transistors are the problem later today
and I'll let you know how that went. Thanks again =)

[Pat70]

I hope you get this fixed Jaguarwong! I hate having sold this Aero with this acting up...
Help this man!

[JaguarWong]

Ha ha, forget about it Pat7o =) Fixing it is half of the fun !

Anyway, a little update: I swapped the transistors.
However in the process I seem to have killed both transistors now =)
Ha ha. But silverlining, now it only displays green (left that one alone)
So it seems the red transistor was the problem all along. Great tip !

So next step, where do I get 2 new transistors, are these pretty common ?
Can I just get em from any electronics store or should I get em from Japan
or someting ?

[grantspain]

the drive transistors are 2sc4001
these are specialist transistors although were common once,check ebay

you also need to check the track to these transistors and the soldering around the crt socket

[JaguarWong]

I just re-checked the transistors, turns out the blue one was just badly soldered.
So I resoldered both and now I'm back to my original situation, with the red and
blue transistors switched. So this leads me to believe the transistors are not the
problem.

I'm goanne check the complete solder track for the red lead on the neck board now.
Thanks for all the support and tips up till now !

[shess]

I had a similar problem with my monitor; there were 3 transistors for RGB on the neckboard as well as 3 more on the chassis. The chassis transistors were the problem in my case, replace all three and now my colors are back. You'll need to find a schematic or a manual to figure out which transistors need to be replaced.

[grantspain]

here is the ms8 schem but it does not show the neck card-

ms8schematic.jpg

[shess]

Well it's kind of strange compared to my other monitors as they have the RGB going directly to the transistors and then branch out from there. On the schematic that doesn't appear to be the case. But general guideline is to look for a group of 3 identical transistors. You could also use a multimeter (in continuity mode) and put one end on the color input and then the other on the transistor legs to see which one is in the path.

[JaguarWong]

Guys that's amazing ! Thanks so much for all the info, this is really helping out.
I'll measure the other transistors tomorrow and the schematic is excellent !
I'm hunting down a replacement transistor for the neck board atm cause I still
don't really trust it. After that I'll be testing the ones on the baseboard.
Thanks, I'll keep you guys posted.

[grantspain]

important to note that the ms8 chassis neck card i have in front of me has the extra transistors on it-the neck card number is 05C02108A1
the transistors to check are
Q302,303,304,312,313,314,322,323,324
the drive transistors are 302,312 and 322
you need to check all those circuits

[JaguarWong]

Well I've been to some of my local electronics stores, none of them had the 2sc4001 transistors
so I'll be ordering some from ebay. Till they arrive the project is dead in the water.
Thanks for the help so far and I let you know if the new transistor worked when it arrives.

[JaguarWong]

Well the transistors I ordered arrived last week so I've been taking another
look at this monitor. The situation before the drive transistors (2sc4001)
arrived was that red was dead and blue was dead. Blue being dead was definitely
caused by a faulty transistor (cause I broke it myself =D).
So I swapped the blue and red drive transistors with new ones that just arrived.
Blue worked again cause of this, but red was still dead...

So I swapped the red and blue wire that came from the base board to the neck-
board. Turns out if I hook the blue wire to the red solder point on the neckboard
all the blue goes red. And if I hook up the red to the blue, nothing happens, no
red, no blue, just green. So my conclusion from this is that there is no red signal
coming from the baseboard to the neckboard. (Is this conclusion right ?).

So I focused on the base board, looking for those 3 identical transistors, but I
can't really find em. Does anyone know their numbers ?
Or does anyone have any stuff I can check on the baseboard ? I'm currently
leaving the monitor on to see if red comes back after some time to see if
it's a heat problem.

Thanks for any tips !

[grantspain]

they are on the neck card

[JaguarWong]

Yeah I think I found and replaced those.
I was looking for the ones shess was talking about on the chassis:

I had a similar problem with my monitor; there were 3 transistors for RGB on the neckboard as well as 3 more on the chassis. The chassis transistors were the problem in my case, replace all three and now my colors are back. You'll need to find a schematic or a manual to figure out which transistors need to be replaced.

I think he meant on the mail/big board right ?

Btw, if all fails, where would one get a replacement chassis set ?

[JaguarWong]

Actually what I'm mostly interested in now if my little theory
about the problem being the main board and not the neck board
is correct. So I can shift my focus from the neck board to the
main board... Can anyone confirm this ?

So the theory is as follows:
I desolder the red wire that comes from the mainboard
into the neck board, result: no red.
Then I desolder the blue wire from the neck board, result:
no red, no blue.
Then I solder that blue wire to the red solder point on the
neck board, result: all the blue is now red.
Then I solder that red wire to the blue solder point on the
neckboard, result: same as above, nothing changes. (One
would have expected the red to go blue)
My conclusion: There's no red signal coming from the
mainboard, therefore I should focus on the main board
instead of on the neck board.

Sorry for all the questions btw, I'm working with a limited
set of skills and knowledge here =)

[grantspain]

yes your theory is correct,but here's the bummer-the signal from the main board comes straight from the custom ic so unless either red pot is damaged or the diodes in that circuit are then you looking at a fault with the custom ic and they are smt components

[JaguarWong]

Right, that's a slight bummer indeed. Well I'll measure the diodes and pots again to be
sure, but it looks like I'll be looking for a new ms8 chassis soon =)

Thanks for everything, I'll let you guys know how this turned out in the end...