• Please review our updated Terms and Rules here

Amdek Video 300 (Composite Greenscreen) Monitor

T

Turbo10

Member
Joined
Jun 1, 2011
Messages
29
Location
West Coast, USA
I have an old Amdek Video 300 (Composite input - Green-screen) monitor that used to accompany a CGA card and my old IBM PC. I remember the video display signal on it "collapsing" so to speak (the display collapsed into a single horizontal line -- this was about 15 years ago probably).

Anyways, just today I pulled it out of the closet and took it apart.

Not surprisingly, the V-SIZE component on the circuit board inside is broken off and it looks to be a variable resistor (or variable capacitor perhaps?) I see R306 silk-screened on the circuit board where the V-SIZE component was previously attached to the circuit board. The V-LIN adjustment (R307) next to it is also a variable adjustment component, and I measured it with my multimeter and it shows a .09 Ohms to .18 Ohms range as I turn the plastic adjustment screw.

Unfortunately the broken part (r306) isn't inside the case anymore, so does anyone know what might be a suitable replacement for the V-SIZE part? I can't seem to find a schematic online.

Thanks!
 
Turbo10 said:
Not surprisingly, the V-SIZE component on the circuit board inside is broken off and it looks to be a variable resistor (or variable capacitor perhaps?) I see R306 silk-screened on the circuit board where the V-SIZE component was previously attached to the circuit board.
Click to expand...
The "R" in "R306" means that it is highly likely to be a resistor (the common naming convention).

Turbo10 said:
The V-LIN adjustment (R307) next to it is also a variable adjustment component, and I measured it with my multimeter and it shows a .09 Ohms to .18 Ohms range as I turn the plastic adjustment screw.
Click to expand...
I'm sure that you are doing that whilst the resistor is in-circuit (soldered on to the board). You'll discover its true value if you measure it out-of-circuit (removed from the board), however, being a linearity adjustment, it won't bear any relationship to a size adjustment.

Turbo10 said:
Unfortunately the broken part (r306) isn't inside the case anymore, so does anyone know what might be a suitable replacement for the V-SIZE part? I can't seem to find a schematic online.
Click to expand...
Different make/models of monitors use different values. What you could do is experiment. Try a 100 KOhm variable resistor, set initially to its mid range setting (12 o'clock). Then see if adjusting that between the 9 o'clock and 3 o'clock positions gets you the desired height. If not, then try the same procedure using a 10 KOhm part. Then down to 10 KOhm, and so on. There are no guarantees with that procedure, and a potential for damage. It all comes down to how the monitor is designed.

For comparison only, the V-SIZE variable resistor on the genuine IBM CGA monitor (model 5153) is 500 Ohms. In the IBM EGA monitor (5154), it is 1 KOhm.
 
Thanks very much for the insight.

Although I initially didn't have any luck finding a schematic, a little more searching later revealed a place online that might have a schematic (for a few bucks). If that comes through, I'll post back here with the correct range.

Otherwise, I'll start with the 100 kOhm resistor and work my way down as you prescribed. Thanks again! I appreciate it
 
Would this work with an IBM PC compatible running a Hercules graphics card? Is there an Amdek monochrome monitor for PCs using MDA/Hercules?
 
As an update (I forgot to post my findings earlier)

The V-SIZE resistor is a 20k Ohm trimmer and the V-LIN (linearity) is a 1k Ohm trimmer.

------------------------------------

Also in response to Team Rocket:

This particular AMDEK monitor (VIDEO-300) only has the composite video input (RCA connector), as opposed to the traditional 9-pin (D-shell) TTL-type input. In fact, you can hook it up to a VCR or other device outputting composite video and it you can watch movies in all sorts of shades of green! :)

My CGA board has both the composite output and the 9-pin TTL output. But, I don't believe I've ever seen an MDA or Hercules board with a composite output, only the 9-pin (D-shell) TTL output.

------But-----

For a MDA or Hercules card with 9-pin TTL output, try the Amdek "Video-310A". This is also a monochrome (amber) monitor and uses:

1 Ground
2 Ground
3 Not Connected
4 Not Connected
5 Not Connected
6 Intensity
7 Video
8 Horizontal Sync
9 Vertical Sync

as the pin specifications on its data cable, which matches the MDA/Hercules pinout spec.
 
"you can watch movies in all sorts of shades of green!"

I was doing that tonight on my Zenith green screen monitor.



~Paul.

With two Ninja Turtles stickers on it and one SMB2 sticker.
 
Is there an Amdek MDA monitor with a green display? I prefer green to amber, unless the amber is particularly orange. I can't stand when they display in pure yellow.
 
Amdek 300A circuit Diagram

Amdek 300A circuit Diagram

Hi there,

I am trying to resurrect an Amdek 300A monitor for use on an apple.

The main board looks ok, but there is some damage in the horizontal out area, possibly a cap and or inductor, possibly the HOT is blown.

Did you end up finding a circuit diagram for this monitor?

Cheers, Martin...



Turbo10 said:
As an update (I forgot to post my findings earlier)

The V-SIZE resistor is a 20k Ohm trimmer and the V-LIN (linearity) is a 1k Ohm trimmer.

------------------------------------

Also in response to Team Rocket:

This particular AMDEK monitor (VIDEO-300) only has the composite video input (RCA connector), as opposed to the traditional 9-pin (D-shell) TTL-type input. In fact, you can hook it up to a VCR or other device outputting composite video and it you can watch movies in all sorts of shades of green! :)

My CGA board has both the composite output and the 9-pin TTL output. But, I don't believe I've ever seen an MDA or Hercules board with a composite output, only the 9-pin (D-shell) TTL output.

------But-----

For a MDA or Hercules card with 9-pin TTL output, try the Amdek "Video-310A". This is also a monochrome (amber) monitor and uses:

1 Ground
2 Ground
3 Not Connected
4 Not Connected
5 Not Connected
6 Intensity
7 Video
8 Horizontal Sync
9 Vertical Sync

as the pin specifications on its data cable, which matches the MDA/Hercules pinout spec.
Click to expand...
 
TeamRocketReviews said:
Is there an Amdek MDA monitor with a green display? I prefer green to amber, unless the amber is particularly orange. I can't stand when they display in pure yellow.
Click to expand...

Amdek's monochrome composite monitors were available with green, amber, or, "white" phosphor. I put "white" in quotation marks, because I saw one of those once, and to my eyes it looked closer to light blue (almost cyan) than white.
 
Hello. I did end up finding and buying a schematic on Ebay. Now the only problem is that I packed up the schematic with the replacement trimmers I purchased so that it'd all be together when I found time to solder it back together.

I'll look for that that box and when I find it, I'll scan the schematic and can post a version here for everyone.

mnc1959 said:
Hi there,

I am trying to resurrect an Amdek 300A monitor for use on an apple.

The main board looks ok, but there is some damage in the horizontal out area, possibly a cap and or inductor, possibly the HOT is blown.

Did you end up finding a circuit diagram for this monitor?

Cheers, Martin...
Click to expand...
 
You must log in or register to reply here.
Back
Top