Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!usc!zaphod.mps.ohio-state.edu!caen!uflorida!mailer.cc.fsu.edu!prism!gp310ad From: gp310ad@prism.gatech.EDU (ROBERT DUCKWORTH) Newsgroups: comp.sys.ibm.pc.hardware Subject: Re: IBM Professional Graphics Dislpay and VGA...how? Message-ID: <26581@hydra.gatech.EDU> Date: 18 Apr 91 01:39:03 GMT References: <1991Apr17.193459.2069@ux1.cso.uiuc.edu> Distribution: usa Organization: Georgia Institute of Technology Lines: 73 Hi- The IBM PG monitor is an analog RGB monitor requireing a composite sync signal (horizontal and vertical mixed).. The monitor supports two modes. 640x480 and 640x400. The mode is changed by pulling the mode line low. The VGA monitor is an analog RGB monitor. It requires a split sync signal (horizontal and vertical on separate wires). The monitor supports 3 modes. 640x480, 640x400, and 640x350. The mode information is in the polarity of the sync signal. Inside the PG monitor the composite sync is split into vertical and horizontal components (pretty easy with an RC filter as one is 10's of kilohertz and the other is 10's of hertz). This is a good place to put the new sync signals in. The problem is that the polarity has to be right.  So, how do we change the varying polarity of the VGA to the constant polarity required by the PG? I used a quad exclusive or and some R and some C. This circuit goes on a small board inside the monitor. It is held in place with hot melt glue or double sided foam tape. Barge cement should do a good job too. What about the mode? Well, the caps hold the average value of the sync signal and can spare enough juice to turn on a 2n3904. this signal goes to the old mode input (gives you two modes). Pick the two that fit the SW you use or.......... The mode is changed by switching in some trimmers on the vertical 'chip' They are switched by one section of a quad 2 to 1 mux (or a 4pdt analog switch if you prefer). here is enough room on the board to replace this with a dual 4 to 1 mux (2p4t switch). Add an extra trimmer and you are 100% VGA compatible. I made boards and bought parts for 1000 kits. We converted 800 monitors and sold all the other kits. So, I'm out of kits. If there is sufficient interest here, I will gather parts for some more kits. Kits include everything needed for a complete (to 100% VGA compatibility) conversion. Manual, 15pin connector, syncfix (copyright) board, trimmer, wire, and all components. Complete kits are $39.95 and also work with many other surplus monitors requiring a 'fixed' sync. I highly recommend NOT generating a composite sync signal. The additional delay caused by the sync fixing circuitry and then by mixing the sync signals puts the sync behind the dots enough to make it difficult to adjust many monitors. As for the kits, I will need a minimum of 10 orders to cover the cost of a minimum board run. It will take about 3 weeks from the time I know there is enough interest til the time all the parts are here and ready to ship. Feel free to roll your own. There's enough info here to do it. :-) Have fun and watch out for sharp edges and HIGH VOLTAGE inside the PG. Also, be careful of the tube neck. Try out your monitor before converting. There is generally enough brightness to see if you get a raster. If you do, It's probably good. If you have problems with 'pincusion' it's most likely from component aging in the E-W amp. Another common problem area with this monitor is the connection between the video board and the main board. Clean the contacts if the colors are off a little or if one is completely missing and you know it is getting to the input side of the video board. Bob -- Bob Duckworth -everything you know is wrong- Earth & Atmospheric Sciences, Georgia Tech, Atlanta, 30332 uucp: ...!{allegra,amdmhplabs,ut-ngp}!gatech!prism!gp310ad Internet: gp310ad@prism.gatech.edu 404-894-3890(o) 874-5051(h) 313-0095(m)