Converting from CRT to LCD or anyone know about video signal

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Converting from CRT to LCD or anyone know about video signal

Postby Jerry » Sat Feb 26, 2011 11:39 pm

A member of one of the other forums I am on kindly gave me a dead anilam superwizard DRO box.

Got the unit home and started poking around. First thing I found was the switching power supply was dead. Tried to resurrect it but no go. Found another lying around and made up a cable to get power to it. Turned it on and all the leds inside came up but no video. No flyback noise but filament glow. After a while of messing around I pull the CRT board (hantarex MT3000) and found it had been hacked on before. Pretty badly too. I found a schematic on line but it is almost useless. Cant hardly read it.

So, I figured before I went any further I would check the video signal going into the board and see if the unit was even outputting anything useful. It looks like it is. The video signal is outputting and the data appears to be changing so I think it is still working. It has three lines out, Video, H and V Syncs.

I am attaching the screen shots from my scope. From the pic it looks like a pretty generic NTSC signal and the sync seems to be included. Anyone know more than me. I am thinking of just using a generic NTSC in panel if thats what this is.

-Jerry

Vertical Sync

Image
Untitled by macona, on Flickr

Horizontal Sync:

Image
Untitled by macona, on Flickr

Video:

Image
Video signals by macona, on Flickr
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Re: Converting from CRT to LCD or anyone know about video si

Postby johnf » Sun Feb 27, 2011 1:24 am

Jerry
Bottom pic looks llike what I would expect
this shows picture info top third of normal screen.

tyry standard video in --should work
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Re: Converting from CRT to LCD or anyone know about video si

Postby Jerry » Sun Feb 27, 2011 5:13 am

After going through the datasheet on the monitor the jumper setting are for TTL Video with separate H and V sync signals. That would explain the high signal. It should be about 1v p-p and I am getting about 2.5v. I found a TTL to composite adapter that mixes all three signals into one composite signal. So hopefull that will do the trick.

If not have been playing around with the original monitor. The flyback is pulling way too much current. Think the primary is shorted. If I cant get something else working I will try to get another one for it.
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Re: Converting from CRT to LCD or anyone know about video si

Postby Doug Coulter » Sun Feb 27, 2011 12:51 pm

From a few years working in a TV repair shop (as the stereo guy). Nearly all HV issues with CRT's are at the HV end of the chain, eg, maybe a bad diode or stack, nowadays often cast into the flyback. We almost never saw a primary short, but in the really old ones (full voltage flyback, separate diode) we did see some secondary shorts/arcs, but not that often. Once in a blue moon, it would be the deflection yoke, which stores part of the flyback energy in nearly all designs. These can be tough to find, as you can't really measure the Q of the inductor(s) that well in the circuit, due to focus supply and main rectifier loading, and various damping applied (resistive) to the circuit to get a smooth ramp and low ringing after the flyback pulse.

We also changed one heck of a lot of horizontal output devices, both the driver and the damping diode (and for this, it didn't matter if it was tube or solid state). Those really take a pounding, and some output transistors fail "leaky" and won't turn off like they should -- This was in general less frequent than failures on the HV side of things.

All those fit your symptoms on the original monitor.

Looks to me like with that large composite signal all you really need is an attenuator to drive something else at standard levels...A lot of stuff uses the height (depth) of the composite snyc to auto adjust the black levels and gain (DC restoration and contrast) so you might not need anything at all. NTSC is full of specs that allow things like that to be done to make TV's "more automatic", which was important back in the day with all that drift in both the signal and the set. Many of the old "dumb terminals" used a video section that this would drive straight up, no mods at all -- if you can find one, most hit the dumpsters a long while back.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: Converting from CRT to LCD or anyone know about video si

Postby johnf » Sun Feb 27, 2011 2:53 pm

Try loading the signal with 75 ohms it may come right
Two 150 ohm resistors in parallel is the norm
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Re: Converting from CRT to LCD or anyone know about video si

Postby Jerry » Sun Feb 27, 2011 4:12 pm

I actually got the symptoms backwards, no filament glow and a weak flyback noise. Something in the HV circuit is pulling the voltage down big time. From what I was reading on the net the Hantarex monitors are good monitors but they have flyback issues.

I did load it down last night. The signal is still over 2v p-p.

I found this little guy and ordered one. For the price I cant even make one:

http://www.alltronics.com/cgi-bin/categ ... tem=92C024
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Re: Converting from CRT to LCD or anyone know about video si

Postby Jerry » Mon Feb 28, 2011 11:01 pm

I got my little ntsc in LCD from work today and made up a voltage divider to get the voltages down to standard composite levels. Connected the lcd and heres what I got:

Image
Anilam Superwizard by macona, on Flickr

Woohoo, it works. I hooked up a spare scale I had lying around and it seems to work. The unit was designed to handle up to 4 scales but two of the locations for the plugs have been covered and holes drilled in the connector location on the board. But the traces are pretty obvious.

This LCD is not going to work though. Cant read much because of the low resolution. And its a pretty old LCD with a terrible viewing angle too. But I know it works now and I think its worth getting going. Looks like a really advanced unit.
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Re: Converting from CRT to LCD or anyone know about video si

Postby Jerry » Tue Mar 01, 2011 2:45 am

I picked up an old Heathkit yoke and flyback ring tester from a guy tonight. I tried it and am not getting much. I pulled the flyback out of the circuit and B+ went back up to about normal. Think it could be a bad flyback?
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Re: Converting from CRT to LCD or anyone know about video si

Postby Doug Coulter » Tue Mar 01, 2011 10:59 am

Without some more info, hard to say about the flyback, but that would be "high odds" if the driver is good. Many old TV sets used a signal off the damper diode to make a b+ boost...and wouldn't have a b+ rise in this condition for example. Yours probably doesn't (most B/W monitors didn't and just ran of 12v) but I can't know. Usually a flyback is driven by an open-collector type output, so if that's bad, disconnecting the flyback would reduce current too. Most sets and monitors use some timing signals derived from the flyback in the loop that keeps sync, and does DC restoration (so black is black) -- so pulling out something that major can be expected to change a lot of things as it would open some feedback loops which would then limit off-scale.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: Converting from CRT to LCD or anyone know about video si

Postby Jerry » Tue Mar 01, 2011 1:10 pm

Here is a link to the schematic if that would help.

http://www.meritgames.com/service%20center/Hantarex.jpg

I figure I am just going to replace all the power semis, old electrolytics, and the non-polar cap after the yoke as well. Looks like the flyback is $56. There was a revised version that superseded the old one.
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