SM124 Small Image?

[800_Rocks]

I just unboxed my first SM124 and it works!!  With my 1040STE.  The image looks good but smallish. There are no external adjustments other than Brightness and Contrast. Is there a way to adjust the image to be larger (to use more of the screen real estate)?  OR is it time to replace caps?  Thanks in advance for your ideas/advice. 

 

[Umberto]

That's the way is supposed to look. I believe Lace scan will give you more image area, but its a hardware mod. 

[+Stephen]

I've heard people mention this before.  What an awful design.  An already small 12" screen with 8" of usable space.

[800_Rocks]

Update: 

1) I got some replies via FaceBook.  The most informative are added here:

- I modified mine back then using the internal pots. I do recall there were claims that when you do so it was pulling "more power" through other components that could cause them to fail.
I have no idea if there were any truth behind those claims though.

- Yes. There were several ways to do this, and at least one of the published methods was responsible for a large stack of dead SM-124 monitors. From what I remember, but this may be oversimplified, the correct way to do this required careful tuning of horizontal and vertical parameters which was difficult to get right. But there was also an 'easy fix' published in some magazine which increased the screen size in perfect ratio by tuning one pot, but that increased the voltage on the beam controls and eventually killed the monitor.

- You can, and it is not advised. By expanding the screen size you could push the deviation circuit too much and fry it. I have adjusted all mines and never ran into problems (well, there are many other problems you can run into but never fried one. For example, there is a capacitor by the adjustable inductor that is prone to high-pitch ringing).
Anyways, if you open it, make sure you know what you’re doing!

- You have to remove the back cover and use a plastic screwdriver (no metal!!) to adjust. It's quite dangerous (high voltages) ... Your viewable screen is also not in the centre, right border is much bigger..

- Old caps that are not used in decades also run the risk of drying out. I have a similar vintage C1802 monitor that, when I received it, had terrible vertical height compression and horizontal distortion. I noticed that after I had it on for 20 - 30 minutes, the picture started expanding and filling out a little bit. After a couple hours it expanded a little more. So I made it a point to power it up and feed it a signal every day for a couple hours to see if it would continue improving and sure enough, after 10 days or so, it looks almost perfect. There’s still a bit of trapezoidal distortion at the top right, but it’s not bad at all for a 33 year old screen. So yeah, some dried out electrolytics can be “re-formed” by doing what I did . I *should* disassemble it, replace those caps and do some geometry adjustments but I’m getting too old to find excitement in possible electrocution

- It's not hard, but dangerous voltages are present. Also, there is a NP cap that should be replaced with a film cap, apparently the word is that cap can be stressed by "expanding" the horizontal & vertical size of the display.

 

2) Also, I found this video that is helpful.  Seems there are a number of pots (only accessible inside) that could perhaps provide more vertical screen image.  I will give it a try.  

 

[Zogging Hell]

I had one monitor that had the screen expansion mod done and it did indeed go down after some use. There is a fix http://www-ftp.lip6.fr/pub/atari/Docs/dead_mon.txt that suggests replacing the faulty component with a higher spec one that can handle the increased stress. So if you want to go down the screen expansion route you may also wish to do that mod as well.

[tjlazer]

I would just do the adjustment to center it and leave it as is.