Yep more Monochrome Monitor Qs - Videokarma.org TV - Video

TinCanAlley · #1 11-12-2021, 04:11 PM

Well I want to start work on another green monochrome monitor, but this one has nothing I can find on the internet and no schematics. I did manage to trace the socket board on the neck and found it has the exact same pins, in the same order, as my IBM, TRS-80 and RCA B&W TV. That means socket CR7 from the BK tester will work, but I don't think there is a problem with the CRT, it has to be in one of the circuits.

When turned on, it gets not raster, even at the highest settings. However, it does have a collapsing raster when turned off. I'm assuming that's some kind of bleed off of HV?

Now this monitor does differ from the IBM in that it has both horizontal and vertical as noted on the circuit board. That means it should produce a raster under higher brightness settings. The know on the front is all the way up and so is the subbright on the board. I don't know what the resistance for those is supposed to be, so testing for anything other than being open wouldn't help much.

So this leads me to 2 questions. Since my DMM goes up to 600V, and this monitor (other than the HV) should be higher than that, can I use it to check all but the HV voltages at the CRT? Also, what areas should I pay particular attention to?

Oh, and there is a composite lead from the power board to the CRT neck board that I have never seen before. I don't know what it is providing as these types aren't used for power, but RF.

Lastly, the IBM has no horizontal or vertical, so the monochrome adapter provides those on pins in the connector plug. Since this has those circuits, is that video adapter useless on a monitor like this, or will it ignore those signals? I beginning to wonder if this monitor is from some kind of data terminal. Maybe it wasn't designed for the PC.

I'm attaching some pics that might be of use/interest.

TinCanAlley · #2 11-12-2021, 04:36 PM

Okay, went ahead and took some voltages. With brightness and contrast down, I get a G1 of -71V, K of 80V, G2 of 620V, G3 of 250V and heater is 11.7V. Now if I turn up the brightness, the G1 starts dropping until full turn on the control and then it is 0V.

Yamamaya42 · #3 11-12-2021, 05:35 PM

If the video connection is the same as the IBM monitor, and it most likely is, then it is on of many clone monitors, and has TTL input, meaning that the CRT is cut off completely until there is input from the video card, so no matter how much you turn up the screen controls, you will not see anything

Sent from my VS501 using Tapatalk

TinCanAlley · #4 11-12-2021, 06:28 PM

Quote:

Originally Posted by Yamamaya42

If the video connection is the same as the IBM monitor, and it most likely is, then it is on of many clone monitors, and has TTL input, meaning that the CRT is cut off completely until there is input from the video card, so no matter how much you turn up the screen controls, you will not see anything

Sent from my VS501 using Tapatalk

So it can have horizontal adjustments on the board even if it doesn't generate the signal? How would I know if it is generating the H signal as opposed to receiving it from the video card? Also, why would there be an RF connection to the CRT neck board?

It has the exact number and pin position as the IBM, but without schematics, I have no idea what they are, other than the first two that seem to be grounds.

I'm getting better at following schematics, but not there yet following traces.

Electronic M · #5 11-12-2021, 07:16 PM

I think what Yamamaya42 is getting at is that despite the monitor generating it's own horizontal and raster, the video stage is designed to bias off all gun emissions until there is a video signal.

Some projection televisions have similar circuits to prevent screen burn if deflection fails.

Yamamaya42 · #6 11-12-2021, 09:06 PM

Quote:

Originally Posted by Electronic M

I think what Yamamaya42 is getting at is that despite the monitor generating it's own horizontal and raster, the video stage is designed to bias off all gun emissions until there is a video signal.

Some projection televisions have similar circuits to prevent screen burn if deflection fails.

Correct, by design, w/o any input from the card, all flow of electrons to the screen are cut off.
this is so they can get as sharp as a display of the letters as they can, this is NOT like any analog display. but under TTL input control.
https://tunneler.org/files/IBM-Techn...2-Hardware.pdf

that shielded link you are seeing is NOT and RF cable, but most likely a shielded path for the TTL coding to the amp on the CRT pcb.

the early IBM mono cards were VERY limited in what they could display, having on/ off reverse or underline or combo there of, that was until The Hercules Graphics Card (HGC) and changed everything.

They found a way to cheat and show graphics on a monochrome monitor.

TinCanAlley · #7 11-12-2021, 10:03 PM

Is it possible to have horizontal pots, but no built in horizontal signal? If so, that would explain the addition of the H pot and H coil (width I think) on the canon, where there are none on the IBM.

I doubt I will blow up anything connecting the monitor to the video adapter, but just want to make sure. The card is due in Monday, so by Monday evening we should have some idea if these two monitors work.

zeno · #8 11-13-2021, 05:50 PM

First off the monitor was built by Panasonic. If its still there you could look
up FCC ID numbers & get the Panny model ##. Do that at FCC.GOV
This is how we got manuals for no name monitors. Cross the FCC ID
& get "mothers" name for the set !

When checking B&W CRT voltages the cathode is important.
If it is high you get little or no brite. If it goes too low
the pix will be to bright.

Flash on turn off
HV is up & the other voltages discharge FASTER & the cathode is hot so
still shooting electrons. Many old B&W TV's had a spot killer circuit.

Your main problem is if these sets do not see a horz sync pulse the video
will be blanked out even if the monitor is perfect.

73 Zeno

LFOD !

TinCanAlley · #9 11-13-2021, 09:52 PM

Quote:

Originally Posted by zeno

First off the monitor was built by Panasonic. If its still there you could look
up FCC ID numbers & get the Panny model ##. Do that at FCC.GOV
This is how we got manuals for no name monitors. Cross the FCC ID
& get "mothers" name for the set !

When checking B&W CRT voltages the cathode is important.
If it is high you get little or no brite. If it goes too low
the pix will be to bright.

Flash on turn off
HV is up & the other voltages discharge FASTER & the cathode is hot so
still shooting electrons. Many old B&W TV's had a spot killer circuit.

Your main problem is if these sets do not see a horz sync pulse the video
will be blanked out even if the monitor is perfect.

73 Zeno

LFOD !

I'm starting to understand the blank screens, now. I can't feed it a H sync until my video card arrives. I only have a color CGA card and it will damage these monochrome monitors if I try it, so I had to buy one. The first one never arrived and the seller said they couldn't find it. So I had to order from another seller and hopefully it will be here by Tuesday. I am hoping that there is nothing wrong with either of these monitors when connected. If not, at least I'll be able to troubleshoot better when they have a signal.

I will start my search for the monitor info with the info you provided. Wish me luck.

Thanks!

TinCanAlley · #10 11-17-2021, 05:28 PM

Okay, I finally got a monochrome video adapter after 2 failed attempts.

The IBM 5151 monochrome works like a charm w/no burn-in and only a scratchy brightness control that deoxit should fix.

The Canon isn't displaying an image, but it is doing something odd. I am used to it not displaying a raster with no signal, and the flash of a raster upon turning it off (the raster shows up and then collapses to the bottom of the screen. However, when I turn it off while connected, the shutdown raster contains the image of what it should be displaying while on. Does anyone know why it won't display the image? What part of the circuitry should I be looking at? I'm guessing the signal is there, but not triggering the HV to display it, and when I shut it off, the shutdown circuit that kicks in and drains the HV causes the image to be displayed. Why? Now that part is beyond me as I have never seen such behavior before.

Thanks!

Electronic M · #11 11-17-2021, 07:48 PM

Probably either the video amp chain, CRT bias circuit, or protection circuits have a fault.
It's anyone's guess without a schematic and voltage measurements.

Another possibility is if the CRT gets it's G2 bias from the B+ boost system and the boost diode and or filter failed that could cause no raster till shutdown. I had that problem on a roundy color TV once.

TinCanAlley · #12 11-18-2021, 01:18 PM

Quote:

Originally Posted by Electronic M

Probably either the video amp chain, CRT bias circuit, or protection circuits have a fault.
It's anyone's guess without a schematic and voltage measurements.

Another possibility is if the CRT gets it's G2 bias from the B+ boost system and the boost diode and or filter failed that could cause no raster till shutdown. I had that problem on a roundy color TV once.

I searched and searched for anything on this monitor. I tried the suggestion of FCC ID, etc. Found nothing there that would indicate it being anything other than a CRT device. So finding a schematic is out of the question.

I will redo all the voltages as it now has a signal. Hopefully they will be different than when there was no signal.