stevewa@upvax.UUCP (Steve Ward) (03/13/88)
I recently purchased a Mitsubishi DiamondScan monitor (model AUM1371a) for use on my AT clone. While I really liked the features of the monitor, (TTL/analog/composite inputs, superimopse capability, etc) it suffered from severe pincushioning (the screen "bends" in at the middle). The dealer replaced the monitor for me, and was good enough to lend me a monitor while his supplier back ordered the replacement. When the new monitor arrived, I discovered that it was just as bad, if not worse, than the first one! Naturally I was upset by this. But my dealer was very helpful in tracking down this bug. He called Mitsubishi in California and found out that the pincushioning is a common problem in the early production models of this monitor (Byte's review in the Feb. issue mentions it too). They offered the following solution to improve the monitor's performance. Get a 4.7Kohm, 1/4 watt resistor (this is an extremely common junkbox part) and solder it in parallel with R417 on the PC board on the bottom of the monitor. The resistor must be installed on the SOLDER side of the board. The components are all clearly marked on the board, so there is little danger of putting it in the wrong place. Make sure the resistor is somehow insulated so it won't short out on other solder traces (I used heat shrink tubing around the entire resistor), put the monitor back together, and you are done. I was able to complete the operation in about 25 minutes, and while a small amount of pincushioning is still present, it is barely noticeable. If you are squeamish about opening up the monitor (High voltages ARE present... make sure the monitor has been unplugged for a good while before you dig in to it) a service techinician should be able to do it rather inexpensively. Monitor now works great. Has excellent color and sharpness. I'm using it with the Ahead EGA Wizard/Deluxe card, utilizing the high speed drivers that come with the card (it runs about as fast as a monochrome card under normal DOS operations!) And I have noticed no compatibility problems. An aside...the Ahead board claims VGA BIOS compatibility...Is this good enough for future applications (ie OS/2)? I was able to run MS-Windows 2.03 in VGA mode without any problems. DISCLAIMER--While the monitor patch mentioned above did come from the factory, I cannot assume responsibility for what happens if you try it at home (or work! :-)). No mention was made of warranty violations, but since it was a factory patch, I don't think they would consider it a violation (especially if you have the work done by a Mitsubishi service center). Mitsubishi also says new AUM1371a monitors coming out of the factory have had this problem corrected. Steve Ward stevwa@upvax.UUCP !tektronix!upvax!stevewa
berger@clio.las.uiuc.edu (03/15/88)
The pincushioning is symptomatic of a failing flyback transformer or
inadequate power supply. Older TV's used to have pincushion correction
circuitry - I thought that was less common with newer monitors.
Without a schematic, it's hard to tell what the modification does.
It probably adds a DC bias voltage somewhere. I'd still worry about
inadequate monitor design, and wonder how long it will be before a
more serious problem develops.
Mike Berger
Department of Statistics
Science, Technology, and Society
University of Illinois
berger@clio.las.uiuc.edu
{ihnp4 | convex | pur-ee}!uiucuxc!clio!berger