Testing the video channel on a vintage Audio Analyzer

[heavymod]

If this is in the wrong area, please let me know / move the thread.

I have a circa 1980's Audio Analyzer - unfortunately I do not have the custom CRT that you could purchase back then. I thought I could just get a bunch of adapters and hook it to a modern LCD, but that is not working.

What I am hoping to do is find out if the unit is putting out a decent video signal. I have access to an oscilloscope / DMM and will look for a CRT tomorrow. However, I have to make a decision soon on whether to keep / return it - so hoping to find out if the video signal is _clearly_ broken before I go and purchase a CRT that may/may not work with this unit.



So I want to test the pins on the monitor plug and determine if they are providing a good signal. The device turns on, fan starts, I can detect voltage on the various internal cards. Inside the computer there are 3 pins that go from the "Graphics card" to a DB-15 plug.

http://i.imgur.com/kG3yyLH.jpg
These 3 wires to go a DB15 plug on the back of the computer labeled CRT MONITOR.

When I attach my DMM ( 388-HD ) to the 3 pins that are attached to the card, I get:

PIN1: .3VAC (.06VDC ) .120 Khz
PIN2: .03VAC (.00VDC )
PIN3: .04VAC (.00VDC )

I have not tested with my oscope yet - I am going to do that this evening.


1) What would appropriate voltages be?

2) Am I able to measure these using my DMM ( I read that low HZ signals could be problematic )

3) Aside from plugging in a matching CRT, is there anyway to determine some basic level of functionality?

A manual for a similar unit ( the 201 ) which comes with a built in CRT says it operates at 50hz, which surprised me.. I figured it would be one of the 15hz types.

Any help appreciated!

[ChuckA]

Looks like the unit may use a regular VGA monitor. Which means there isn't a "video" signal, so you'll be looking at red, green, & blue color signals, some sync information, & clock data.

Look here: "http://pinouts.ru/Video/Vga15_pinout.shtml" for the pinout & signals on the connector and if they match up with your connector try a VGA monitor. They may have mixed pins up so you had to buy their monitor.

The board you show is the CPU which appears to be the same as used in the model 201.

The 3 wires going to the connector are probably the RGB output, the only way you can measure and verify that will be with a scope.

Chuck

[heavymod]

Originally Posted by ChuckA

Looks like the unit may use a regular VGA monitor. Which means there isn't a "video" signal, so you'll be looking at red, green, & blue color signals, some sync information, & clock data.

Look here: "http://pinouts.ru/Video/Vga15_pinout.shtml" for the pinout & signals on the connector and if they match up with your connector try a VGA monitor. They may have mixed pins up so you had to buy their monitor.

The board you show is the CPU which appears to be the same as used in the model 201.

The 3 wires going to the connector are probably the RGB output, the only way you can measure and verify that will be with a scope.

Chuck

Thanks for the reply - I have a decent db15 to hd15 adapter which has a number of switches on the top for adjusting the pinouts. I had hoped I could just plug it into my modern LCD screen and figure which pins needed to go where. Is that doable?

So a DMM won't pick up the RGB voltages? Right now I'm basically getting no voltage off these 3 pins... and I know it should be putting out a signal on boot.

I'm being an idiot with my oscope - for some reason I can't get readings with the probes, but signal generator to BNC on my scope is working fine. As soon as I plug in the probe and test against the signal generator - I get nothing....
So if there is an alternate way to test, that would rock. I'm pretty new to electronics, so dealing with some real Electronics for Dummies issues here... But if I have to use the scope, no worries I can keep at it.

Do you have experience with the 201?

[ChuckA]

You could plug it in to a VGA LCD monitor and see what happens.

The DMM won't give you any meaningful information, look at this site:" https://www.ramelectronics.net/Converting-VGA-HDMI.aspx ", not for the information so much as for the picture of the RGB signals you want to see on the scope. These are static from a color bar test pattern, yours will be a bit different depending on the screen display.

You should have a calibrator output point on the front of the scope, connect probe to that to check probe, also make sure you have triggering set to auto.

Have never worked with any of the RE equipment, just seen some of their documentation. Most of my analyzers are HP.

Chuck

[kf4rca]

I think it's probably a TTL monitor. That uses separate H and V like VGA but has TTL video on only one pin and it looks like data on a scope (HIGH = 5V).

[heavymod]

Originally Posted by ChuckA

You could plug it in to a VGA LCD monitor and see what happens.

The DMM won't give you any meaningful information, look at this site:" https://www.ramelectronics.net/Converting-VGA-HDMI.aspx ", not for the information so much as for the picture of the RGB signals you want to see on the scope. These are static from a color bar test pattern, yours will be a bit different depending on the screen display.

You should have a calibrator output point on the front of the scope, connect probe to that to check probe, also make sure you have triggering set to auto.

Have never worked with any of the RE equipment, just seen some of their documentation. Most of my analyzers are HP.

Chuck

Thanks this is helpful - looked at some RGB waveforms, and am currently testing my ability to see those on a working LCD monitor. Having trouble with the triggering I think. I do have triggering to auto, and will check calibration point to ensure probe is working ok.

I do suspect that as the poster above wrote that it is a TTY + hsync + vsync just due to the timing. I don't think the 201 CRT is rgb, so not sure if this one would be.

I'm also going to look up some sync signals so I can be sure I can find them if they are there.

Appreciate the help

[heavymod]

I'm struggling to see video signals using my Tek 485 analog scope. As a test I'm using a 15 pin out VGA from a working computer.

I think I finally got it. Does this look like a proper Red video channel?
http://i.imgur.com/gxFLZUk.jpg

This is one of the 2 sync channels ( v or h , don't remember which )

http://i.imgur.com/mxoVpj2.jpg


If these look good, I'll go back to the RE256 and see if I can see signals on the video channels there...

ps: is there anyway to insert a thumbnail image of a larger pic? I'm used to using [TIMG] but it doesn't work here.

[Electronic M]

The video looks like it probably is video, but you will get more detail if you play with the horizontal time scale knob...1-3 cycles usually gives you the most info.

Wrap [IMG] around your picture links here to get embedded pictures.

[heavymod]

Originally Posted by Electronic M

The video looks like it probably is video, but you will get more detail if you play with the horizontal time scale knob...1-3 cycles usually gives you the most info.

Wrap [IMG] around your picture links here to get embedded pictures.

Awesome, thanks! Now on to test the other device!

Re: Images. I know how to do [IMG] was hoping this board had a "thumbnail" option [TIMG] that just displays a small version and user can click to see full size.. not a big deal just saves me time and I can upload highres images. Or maybe there is a way to reduce the displayed size of the image? I posted one and it was like 3k pixels wide....

[Electronic M]

Use a free image hosting site like Flickr (my choice) or photobucket (use to use them)...They will make the IMG code for you and let you choose from a range of sizes, and it is very easy to do....I just noticed that you use Imgur. Perhaps they have options for size of posting too.