Tektronix 4125 Workstation mystery

I have recently discovered a Tektronix 4125 workstation computer. I have the monitor and the computer. The whole system seems to power up but I get no video (can't even tell if the monitor is turning on other than a noise it makes when degauss is pressed). The keyboard lights up and the fans start in the computer box. I have no idea where to start other than the video cables probably being broken. There seems to be a manual for this thing but I cannot find it online and I only know that it exists. Any info will help, thanks!. 

We have a 4115 at the vintageTEK museum that has the same symptoms. In ours the high voltage in the monitor is dead. It is difficult to work on and we suspect the high voltage transformer for which there are no replacements. We do show a&#160;4110/A/B/4120 SVCE in our microfiche. I don't know what it contains so will have to look when I am at the museum in a few days.<br> <br> I would suggest trying a substitute monitor but I don't remember what the interface is. I'm thinking it is likely R, G, B as that is what it is on the 4115. I just don't remember the details on the 412X series because by that time I was in a different group. Why don't you post a photo of the front and rear of the monitor showing the connections.<br> <br> The other option is to monitor the video signals but that's some work. I suspect there is a battery on the processor card that is dead. The terminal might be stuck waiting for some user input so I don't know what the video signals might be on power up.<br> <br> There are lethal voltages in the monitor so any repair attempts have to be by someone qualified in safety to work on high voltages. I cannot advise on internal monitor troubleshooting or repairs.

Took a closer look, upon some research, I have determined that the computer itself uses composite video out with the BNC video form factor cables. My first step will be to replace the cables since they were torn apart when I found them, so my mediocre repair job probably wasn't doing the trick. The actual computer hardware seems to be good since a bunch of leds on the logic boards came on when I turned the computer on with the case off and they responded to the reset button. If the new video cables do not work, the culprit is possibly the monitor but I won't know for sure until I connect the system to a tv which leads me to a question I have, there is a weird cable called TO DISPLAY that I have no idea what it does other than it connects to the monitor, do you know anything about it. Here is a photo of the connections on the back of the computer.&#160;

I thought it would be RGB as that was typically used in the higher end products. I did search the microfiche today and there is a lot of microfiche on the 4110/41120 series, but it is many of the option boards that are common to both. We do not have any service information on the 4125. Sorry.<br> <br> Dave

It's all good, thank you for your help.&#160;