UFO
Offline
london, UK

This is a long shot, but I can't seem to find anything elsewhere online about this specifically as an issue.

I have a contrast problem with my backlit MGB. When I use it, the contrast consistently fluctuates without me touching the slider. It seems to sometimes be triggered by pressing the A and B buttons, and sometimes it isn't, and instead gets triggered by sounds or changes on the screen.

Furthermore, the contrast gradually gets brighter as it's used, rendering it completely unusable after half an hour of playing with it.

After I turn the system off, it resets to a normal contrast level after a while, but when I turn it back on it immediately starts up with the same issue.

From what I've found online (though my search only found various DMG contrast problems) I should attempt to clean the wheel and general surrounding area. I'll try that ASAP but wanted to make a post detailing the problem to see if anyone knew of any particular causes that might have come to mind beforehand.

Thanks in advance!

Jazzmarazz
Offline
Michigan

This is a problem with the MGB's power source. It is less powerful than a DMG and droops with heavy CPU useage. Do you have an EMS64 cart?
You can try an AC adapter over batteries and this should help. If I remember correctly, there was also a Series to parallel mod for the MGB that essentially increased the Current source, but lowered the voltage. I think it lessened the lifespan of the batteries but increased the performance while they 'did' last.

The problem is present on DMG as well, but mush less noticeable due to the two extra batteries.

Last edited by Jazzmarazz (Dec 10, 2015 12:00 pm)

UFO
Offline
london, UK
Jazzmarazz wrote:

This is a problem with the MGB's power source. It is less powerful than a DMG and droops with heavy CPU useage. Do you have an EMS64 cart?
You can try an AC adapter over batteries and this should help. If I remember correctly, there was also a Series to parallel mod for the MGB that essentially increased the Current source, but lowered the voltage. I think it lessened the lifespan of the batteries but increased the performance while they 'did' last.

The problem is present on DMG as well, but mush less noticeable due to the two extra batteries.

This clears things up a lot, thank you! I have an AC adaptor for DMGs - just bought one for the MGB/CGB in the hopes that it'll do something about the problem.

I'm not sure if I'll be able to install any further mods to help the problem as I'm very inexperienced but I'll look into it. Worth it as I really like using the Pocket system. Thanks again.

Imaginary
Offline
Whateverville, California

I also tend to go with a pretty strong resistor to keep power usage to a minimum. People who like backlights on the brightest setting are usually going to be frustrated with pockets.

UFO
Offline
london, UK
Imaginary wrote:

I also tend to go with a pretty strong resistor to keep power usage to a minimum. People who like backlights on the brightest setting are usually going to be frustrated with pockets.

Excuse my lack of expertise, but what particular type of resistor would this be? :>

Imaginary
Offline
Whateverville, California

100 ohm is a pretty standard value, so something like 250 or 300 will give you a pretty dim screen. You can get a big ol' box of assorted resistors basically anywhere electronics parts are sold. Just throw it in between your light's hot side lead and the power source. Try some different values and see what you like. You can also get a little trimpot and hand-adjust the brightness if that suits you better.

UFO
Offline
london, UK

I'm going to try this! Thank you very much for your help.

jmc1987
Offline
Washington, PA

Yeah, the resistor should take care of the problem. I went through this recently. It actually looks much nicer with the lower brightness, imo.

Koji-Kendo
Offline

You could install a trim potentiometer pretty easily as well. They're cheap and will give you the ability to adjust the brightness on the fly.

Last edited by Koji-Kendo (Dec 11, 2015 4:30 pm)

UFO
Offline
london, UK

I managed to find a 100 ohm resistor and while the backlight is hardly any dimmer, it actually solved the problem. I am still planning on getting the higher values recommended as well as I think a much dimmer brightness level will actually be more convenient and smooth it out further, in instances where the batteries aren't fresh. I then had some flickering problems but quickly realised I'd just soldered it poorly. A lot of screwing and un-screwing was involved. Thank you very much for all of your responses.

katsumbhong
Offline
Taichung, Taiwan
UFO wrote:

I managed to find a 100 ohm resistor and while the backlight is hardly any dimmer, it actually solved the problem. I am still planning on getting the higher values recommended as well as I think a much dimmer brightness level will actually be more convenient and smooth it out further, in instances where the batteries aren't fresh. I then had some flickering problems but quickly realised I'd just soldered it poorly. A lot of screwing and un-screwing was involved. Thank you very much for all of your responses.

If you want to get super geeky, you can get a potentiometer with knob to adjust the brightness on the fly.

Ledfyr
Offline
Sweden

I've been using rechargeable 1.6 volt NiZn batteries for a few months with my MGB.
Contrast fluctuates way less, even when the batteries are low. The only drawback I've noticed is that they discharge quicker when not used than NiMH.

Last edited by Ledfyr (Dec 11, 2015 11:34 pm)