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More monitor fun!

KevinO

Experienced Member
Joined
Apr 13, 2012
Messages
380
Location
Des Moines, IA USA
My efforts to try to connect the video output of my B128 to the RGBI input of one of my other monitors has resulted in a completely different project. I was trying to connect it to a Magnavox CM8762. That monitor sort of worked, but the screen was fuzzy and there was some distortion. I opened it up to tweak the screen pot on the flyback to turn the brightness down, and found that it has the same flyback that I need for one of my 1084s. Since the 1084 is the more valuable monitor (having both RGBI and Analog RGB), I decided to sacrifice the Magnavox to transplant the flyback into my 1084. Got this done with no problems, and now my 1084S is now working again.

...sort of. Composite CVBS/LCA works fine, but nothing from either the analog or digital RGB ports. Then I remembered that I had stupidly shorted something way back when I had removed the original flyback. I had shorted something on the power supply to the digital RGBI board that sticks up from the main board. So I took that from the CM8762 as well. They really are almost the same monitor! No luck. Still no video. Then I found a blown resistor on the main board (R232 I think it was) and replaced that, and now I have RGBI video! I still have one more problem. With nothing plugged in and the switch in the RGB position, the whole screen is blue. Some component in the blue circuitry is still open (or shorted), I think. I was getting bleary-eyed, and it was too late to keep troubleshooting, but I'm going to tackle it again tomorrow night.

I don't know that I'm asking for help, exactly, but just sharing my adventures. I really enjoy actual electronics repair, even if I'm not particularly good at it!
 
Thanks guys...I think! That avatar really is a picture of me....taken on a regular digital camera and digitized with Computereyes on the C64. I tried some serious expressions, but I can't take myself that seriously, so I ended up with what you see here.

I learned the lesson about high voltage circuits when I was 11 years old. I remember it well. A neighbor had given me and old TV to play with, and I decided to take it apart. Naturally I had it turned on 5 minutes before I did this. The tubes (no old people jokes please) came out easily, but I had trouble with "that suction-cup thingie on the back of the tube". So I got my fingers underneath it to get a better grip. The next thing I remember, I was 6 feet away from the TV and not sure how I got there. I have since learned how to discharge the high voltage anode, for anyone who is wondering. :D
 
I had a similar intervention around the same age perhaps a bit younger...

I hung on 230AC more times then i care to count I'll stick with low voltage DC and more important low current designs.

btw talking about monitors what would be the easy way to convert that nasty VGA 1volt top top to TTL logic?

And about the blue circuit you could compare it with the green or red circuit they should have similar resistance.(or similar voltage levels when using a oscilloscope)
 
The 1 V p-p is a analogue signal. Are you trying to convert the level to trigger something, so maybe a gate with a pull-up resistor to clamp the voltage level might work, or to actually extract the video information, in which case you'd need a AD converter of some sort.
patscc
 
Just need to sense the high or low state, no need to have the detail. ;)
I thought i required a cap to decouple and act as a signal filter and use a couple of resistors to clamp the voltage to a tri-state level.
already have the PLL to sync the colour clock, just need a simple A/D conversion.
 
My efforts to try to connect the video output of my B128 to the RGBI input of one of my other monitors has resulted in a completely different project. I was trying to connect it to a Magnavox CM8762. That monitor sort of worked, but the screen was fuzzy and there was some distortion. I opened it up to tweak the screen pot on the flyback to turn the brightness down, and found that it has the same flyback that I need for one of my 1084s. Since the 1084 is the more valuable monitor (having both RGBI and Analog RGB), I decided to sacrifice the Magnavox to transplant the flyback into my 1084. Got this done with no problems, and now my 1084S is now working again.

...sort of. Composite CVBS/LCA works fine, but nothing from either the analog or digital RGB ports. Then I remembered that I had stupidly shorted something way back when I had removed the original flyback. I had shorted something on the power supply to the digital RGBI board that sticks up from the main board. So I took that from the CM8762 as well. They really are almost the same monitor! No luck. Still no video. Then I found a blown resistor on the main board (R232 I think it was) and replaced that, and now I have RGBI video! I still have one more problem. With nothing plugged in and the switch in the RGB position, the whole screen is blue. Some component in the blue circuitry is still open (or shorted), I think. I was getting bleary-eyed, and it was too late to keep troubleshooting, but I'm going to tackle it again tomorrow night.

I don't know that I'm asking for help, exactly, but just sharing my adventures. I really enjoy actual electronics repair, even if I'm not particularly good at it!

IIRC, and it's been a looong time, but the Commodore 1080 monitor that I have I burned out the RGBI input on (by plugging something in that had +12V on one of the lines) and I had to replace an IC that was an analog switch or something. It was the first chip past the connector in the circuit. Of course the 1080 is a completely different beast in the 1084.
 
Yeah, the 1080 and related monitors are Daewoo, I think. They seem to be a much more reliable monitor, but operationally, the NAP-made 1084 has always been my favorite.
 
AC coupling as opposed to DC coupling can distort the signal, although, not having any idea what your app/schematic is, don't know if this would be the case/problem. Is this related to the CC68k project, or something else entirely ?
patscc
 
Yeah, the 1080 and related monitors are Daewoo, I think. They seem to be a much more reliable monitor, but operationally, the NAP-made 1084 has always been my favorite.

Pretty sure this one is a Toshiba. I know Daewoo made the later 1084P monitors though. I think the early square 1084(S) monitors were made by Magnavox, which probably explains why your flyback matched. The specs I've seen on the 1080 online say it's a .42 dot pitch, but that is certainly not the case for this one. I think it's closer to .28.

EDIT: Sorry 1084*D*, not P.
 
Pretty sure this one is a Toshiba. I know Daewoo made the later 1084P monitors though. I think the early square 1084(S) monitors were made by Magnavox, which probably explains why your flyback matched. The specs I've seen on the 1080 online say it's a .42 dot pitch, but that is certainly not the case for this one. I think it's closer to .28.

EDIT: Sorry 1084*D*, not P.

Yeah, you may be right. I have a couple of the late 1084s as well, but neither of them work. The early ones, Toshiba or whatever, never seem to die, but it doesn't seem like they have as good of a picture as the Mangavox (NAP) models.
 
AC coupling as opposed to DC coupling can distort the signal, although, not having any idea what your app/schematic is, don't know if this would be the case/problem. Is this related to the CC68k project, or something else entirely ?
patscc

VGA controlled LED cube build with the 74 logic family of IC's, hey it's a monitor... of sorts! :D
 
I'm pretty sure the 1084 monitors (and many other Commodore monitors from that era) were made by Philips / Magnavox. I had some friends that had 1084's (or 1084S's -- that was the stereo version) and they all looked similar to my Philips CM8833 (also a very common monitor from those days).

My CM8833 had stereo sound, a 50/60Hz switch, an input switch that switched between SCART and TTL-RGBI (I had a PAL TV tuner on the SCART input and a PC with CGA on the RGBI input) and, if I remember correctly, a monochrome switch that would let you change the color picture into green on black.

My friends' monitors may not have had RGBI or SCART (only CVBS) but they were very similar in how the controls were laid out. I believe they were all based on the same Philips chassis which was sold VERY well I'm sure (although I'm biased because I lived in Eindhoven - the home town of Philips in those days).

===Jac
 
Yes, 1084S and CM8833 should be pretty much interchangeable. Earlier 1084 models had other manufacturers like the ones mentioned above and others. Even the 170x, 180x, 190x and so on seem to have been outsourced and then with Commodore casing and labling. Then again, I think it is awfully common and saves a lot of money compared to if every computer manufacturer would have facilities to produce every item from loose parts.
 
Well, I got it fixed, with a little help. I knew it had to be in one of the RGB circuits, because when you switched to CVBS, the screen colors were normal. I kept focusing on the RGBI board and surrounding circuits, because when I cut the blue output line from the RGBI board, the blue screen disappeared.

Anyway, I was out of ideas, so I emailed someone who knows a lot more about monitor repairs than me, and he told me to look downstream from the RGBI board, and not to just assume that the problem has to be before where I cut the trace. It turns out that was what was holding me up. TS219, which is the second amplifier transistor in the analog RGB circuit was conducting emitter to base in both directions. Replaced TS219 and my monitor is working!

Cutting the trace coming RGBI board removed the bias from TS219, which is why the problem went away, but I was looking upstream for the cause, when it was actually downstream! Very good lesson, and one that took 2 months for me to learn.
 
Well, I got it fixed, with a little help. I knew it had to be in one of the RGB circuits, because when you switched to CVBS, the screen colors were normal. I kept focusing on the RGBI board and surrounding circuits, because when I cut the blue output line from the RGBI board, the blue screen disappeared.

Anyway, I was out of ideas, so I emailed someone who knows a lot more about monitor repairs than me, and he told me to look downstream from the RGBI board, and not to just assume that the problem has to be before where I cut the trace. It turns out that was what was holding me up. TS219, which is the second amplifier transistor in the analog RGB circuit was conducting emitter to base in both directions. Replaced TS219 and my monitor is working!

Cutting the trace coming RGBI board removed the bias from TS219, which is why the problem went away, but I was looking upstream for the cause, when it was actually downstream! Very good lesson, and one that took 2 months for me to learn.

Huzzah!
 
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