CM8833 MK2 RGB input problem

[alexh]

Anyone ever taken apart a CM8833 MK2?

Mine works fine in composite mode but I just bought an RGB cable and I notice that the RED input is "stuck" on.

It is not the cable because even with the cable removed with the RGB input selected I get a RED screen instead of a black one.

I don't really want to take it appart if I have no idea what I'm going to doing / looking for, especially as monitors can be a devil to disassemble and put back together. (I've tried it before on a 1084S and never been able to re-assemble it successfully).

Any suggestions? Anyone with photo's of inside? Anything

[Loedown]

Originally Posted by alexh

Anyone ever taken apart a CM8833 MK2?

Mine works fine in composite mode but I just bought an RGB cable and I notice that the RED input is "stuck" on.

It is not the cable because even with the cable removed with the RGB input selected I get a RED screen instead of a black one.

I don't really want to take it appart if I have no idea what I'm going to doing / looking for, especially as monitors can be a devil to disassemble and put back together. (I've tried it before on a 1084S and never been able to re-assemble it successfully).

Any suggestions? Anyone with photo's of inside? Anything

Circuits are floating around in The Zone

TS276 short circuit

D255 short circuit

IC251 / 252 logic problems

Those will be your most likely culprits, monitor section as a TV is working as you get proper colour separation using composite. Nice thing is that you have three inputs side by side, just use a multimeter and check your voltages at each stage and you will quickly work out what is knackered.

[alexh]

Thanks, unfortunately those schematics are for the CM8833 MK1.

The components you refered to are for the 16-colour TTL RGB. I'm using the Analog RGB input.

I do not know if it is of any help diagnostically, but if I switch to TTL input with no cable attached the RED input is still active as I'm getting a RED not black screen.

Does that narrow the search? (Assuming the schematics for the MK2 are similar?)

[Loedown]

Leave it until tomorrow, I will have a dig around, see if I can find the mk2 schematic and advise.

[Jope]

I've been looking for the mk2 schematic too. Or actually one for the 1084-P2.. I want to add s-video in to my 8833-II..

[rkauer]

@Alexh: when an image have a skew to one colour, that means the corresponding transistor on the neck of the tube is shorted, or the associated resistor is burnt.

Check both before anything else. The transistor is an ordinary BC338 of sorts, the resistor is ~1 Mega Ohm.

[Hewitson]

Originally Posted by rkauer

@Alexh: when an image have a skew to one colour, that means the corresponding transistor on the neck of the tube is shorted, or the associated resistor is burnt.

Check both before anything else. The transistor is an ordinary BC338 of sorts, the resistor is ~1 Mega Ohm.

Couldn't agree more, but in this case the composite input works fine.

[alexh]

Originally Posted by Hewitson

Couldn't agree more, but in this case the composite input works fine.

Yup

[Loedown]

Ok, after a bit of digging and trying to decipher Philips SHITFUL numbering system, it seems the CM8833-II is also known as CM11342/05G

I have dumped the full service manual in The Zone, same system applies, check the other two inputs and determine where the signal goes awry. You can do some resistance checks with the power off which may show up a fault or if that shows nothing you will have to do it with power on.

[Jope]

Thanks, saved for future reference..

Ahhh, it seems the Philips branded ones were not made with LCA capability, composite only.

My search for the Commodore branded "new" 1084 schematics continues..

[Hewitson]

This type?

[Loedown]

@Hewitson

The history of the 1084 variances and the Philips monitors are very convoluted, like some other brands of TV, I think it's the Princess brand that uses a Goldstar chassis and how LG was created out of the defunct Goldstar company etc.

Heresay, I could be wrong I could be right says Johnny

[Jope]

Originally Posted by Hewitson

This type?

That's the old style Philips-made 1084 (just about all 1084 schematics on the net are for that).. The one I need schematics for has the power button in the back, basically it's the 8833-II but branded as a Commodore 1084 and switchable composite only / LCA..

Either 1084S-P1 or 1084S-P2

http://gona.atw.hu/Commodore/monitor...el_number.html

Daewoo also made 1084s with the power button in the back, but I doubt those have much else in common except the general case shape.

[Hewitson]

I've put the manual for the P1 in the zone, hopefully it might be of some use but it probably won't be due to it's terrible quality.

[Jope]

Cheers, I'll see if I can make out the missing components from it once I get around to dismantling the 8833-II.. :-)

[alexh]

Originally Posted by Loedown

it seems the CM8833-II is also known as CM11342/05G I have dumped the full service manual in The Zone

Great stuff. Thanks for all your help & tracking this down. Checked and this is the schematic for my monitor.

Originally Posted by Loedown

same system applies, check the other two inputs and determine where the signal goes awry.

Well I know that the RED is ok AFTER the TDA3505 chip because both RGB and CVBS go into this chip and follow the same path out to the Tube and red with CVBS works fine.

VERY strange. If I am reading the schematics correctly, when in linear RGB mode there are no components before the inputs on the TDA3505!

I think that means the fault has to be a wiring fault between the D input and pin 14 on the TDA3505? Or a faulty TDA3505?

http://www.alldatasheet.com/datashee...S/TDA3505.html

[Loedown]

I have some 1084 paper schematics out in the shed, I'll have a look tomorrow when I get back home from work, at least I can tell you what they are and I know they are legible.

[Loedown]

Originally Posted by alexh

Well I know that the RED is ok AFTER the TDA3505 chip because both RGB and CVBS go into this chip and follow the same path out to the Tube and red with CVBS works fine.

VERY strange. If I am reading the schematics correctly, when in linear RGB mode there are no components before the inputs on the TDA3505!

Incorrect, I haven't got much time.

RGB goes through 7320 ( 74LS37 ) & 732x ( 7406 ) on TTL

CVBS bypasses those two on A18 & A17

SK4 could be partially faulty.

RED A4
GREEN A5
BLUE A6

All via 100nF caps into TDA3505

Check TDA3505 pins 13, 14, 15 for 4V, pins 21, 22, 23 for connectivity.

2642, 2643, 2644 22nF caps for O/C S/C

RED pin 1
GREEN pin 3
BLUE pin 5

outputs ^^^^ check for same voltage on all 3

pins 4, 2, 28 the same, around 5.3V

Just look for discrepancies, tell me what you find and I will report back tomorrow, goodnight and pleased the circuit is right. No wonder none of us could find a CM8833-II circuit.

[alexh]

Thanks again.

Not got time to fiddle tonight, but I did notice that if you turn the contrast down that the red goes completely.

I'm sure that is a hint. Will play next week after the UK holiday.

[Loedown]

Originally Posted by Loedown

I have some 1084 paper schematics out in the shed, I'll have a look tomorrow when I get back home from work, at least I can tell you what they are and I know they are legible.

I have dug around and found one marked as 3138 105 21901

This suggests it's a Philips model, there are no additional markings on the schematic.

It has;

1 speaker and 1 speaker input
CVBS / RGB switch
8 pin TTL RGB input ( round )
SCART connector marked as Euro Connector
Video In connector ( RCA )
Green switch
VCR switch

Sound chip is TDA2611A
Vertical Driver chip is TDA2653A
Horizontal Driver chip is TDA2595
RGB Decoder is TDA3505


I haven't pulled a 1084 apart for awhile, so if anyone has an idea, cool, if not I will scan it and Zone it in the upcoming days, schematic quality is excellent.