måndag 20 april 2020 skrev Chris Zach via cctalk <[email protected]>:
> As I wrote earlier in the thread I think it is a good idea to check the V >> sync and H sync signals to check that they are right in pulse length and >> shape. >> > > Good starting point. From the schematics would that be scope probe to J1 > pin 5 for horizontal and j1 pin 9 for vertical? Also which is J1, and how > are they numbered :-) Also is there a good ground reference point? I have a picture of the connector on my page. Have a look there. The connector have the standard color codes to map to numbers. Black for zero, Brown for one. Etc. > > Also is there a document that links the part numbers on the boards with > what's on the schematics? No DEC document. When I did my repair I mapped all ICs to the board but not the connectors, sorry. You can find all here. Including links to schematis and maintenance manual: http://www.datormuseum.se/home/dec-vt5x > There are indeed electrolytic capacitors in the vertical deflection circuit >> but I am not sure if that would make the beam move much faster since for a >> faster move of the beam also requires a higher voltage over the deflection >> coil to create a faster ramp up of the current trough it. But it is >> definitely worth checking. Especially since the scan lines are sloping a >> bit and not straight as one would expect. >> > > I would believe a capacitor failure due to heat, any ones in particular I > should check? C45 and C42 could be useful to check. > > So do I. And now we need Chris to do some measurements on it to get >> further. >> > > More than happy, just haven't worked on TV sets before and would rather > not blow off my hand. I'm guessing the really dangerous voltage is the one > on the bottom left that comes off the step up transformer over to the odd > plug going into the VT52 rear bulkhead (HV to display) What you could do is what I did. To remove all control board on the bottom and lay it out flat on the table. Make a small circuit that create a composite video signal and feed it into a standard composite video monitor or TV set. If you remove a jumper to th CRT logic there will be no HV at all generated. /Mattis > > C >
