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Testing BNC and VGA cable voltage and resistance

J

Joe

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Hello. I want to test cables coming out of a couple of superguns / consolised MVS to check what RGB and sync voltage and resistance they are generating.

I can find lots around general multimeter usage, but surprisingly nothing about testing output voltages and resistance for these kinds of gaming cables.

Is there a good source or video to walk through this, or any key points to consider when using the multimeter on the cable? For example,
- I assume I need to test voltage whilst on, putting one multimeter to the outside of RCA cable and one to the inside pin
- is there any difference in measuring RGB voltage and Ohm with measuring these for the sync line
- is there a chance of damaging the supergun/MVS when using the multimeter etc.

Fyi - one of the setups is taking a sigma 1AV supergun to a Sony BVM, but cannot confirm the supergun has safe RGB and sync levels. I believe TTL sync is 5v but the BVM (A20) can go to a max of 3 or 4v.

Any help appreciated.

Thanks
 
To check these signals you will need an oscilloscope. You won't have a meaningful reading with a multimeter.
The sync signal is in the microsecond range and RGB will vary a lot. You can get an average, so to speak, but it won't tell you anything about the peak values.
You can check the resistance of the cable with a multimeter but, again, it's pretty meaningless.
TTL signals are usually far below 5V. A logic high output is usually around 3V or so. You can read up on this and compare against CMOS where high is, erm, higher.
 
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Joe said:
Hello. I want to test cables coming out of a couple of superguns / consolised MVS to check what RGB and sync voltage and resistance they are generating.

I can find lots around general multimeter usage, but surprisingly nothing about testing output voltages and resistance for these kinds of gaming cables.

Is there a good source or video to walk through this, or any key points to consider when using the multimeter on the cable? For example,
- I assume I need to test voltage whilst on, putting one multimeter to the outside of RCA cable and one to the inside pin
- is there any difference in measuring RGB voltage and Ohm with measuring these for the sync line
- is there a chance of damaging the supergun/MVS when using the multimeter etc.

Fyi - one of the setups is taking a sigma 1AV supergun to a Sony BVM, but cannot confirm the supergun has safe RGB and sync levels. I believe TTL sync is 5v but the BVM (A20) can go to a max of 3 or 4v.

Any help appreciated.

Thanks
Click to expand...
I mean worst case scenario you can just put some resistors inline on the cable to pull it down to a "safe" level. I use a SCART cable with a resistor to take TTL down to 750 Ohm. When I use that cable on my Dreamcast Toro VGA box it works fine even with the pulldown in place.

So if you never know the exact voltage out you'd still be in the clear by pulling a potential voltage down.
 
Thank you both! This rabbit hole is deeper (and more expensive) than I thought. I miss the days as a kid when I just plugged two RCA cables into the front of the TV and got on with enjoying the game. Nowadays it involves a month of research, replete with endless YouTube videos, soldering, vast expense, and tears and pain, before I can finally sit down to a game I have no time to play :)

My hunch is the BVM will handle TTL signals but don't want to risk it.
 
Joe said:
Thank you both! This rabbit hole is deeper (and more expensive) than I thought. I miss the days as a kid when I just plugged two RCA cables into the front of the TV and got on with enjoying the game. Nowadays it involves a month of research, replete with endless YouTube videos, soldering, vast expense, and tears and pain, before I can finally sit down to a game I have no time to play :)

My hunch is the BVM will handle TTL signals but don't want to risk it.
Click to expand...
My PVM’s can so I’d assume the same but you know what they say about assumptions
 
Thanks SD / Awbacon - just when I thought I was out, they pull me back in (i.e. I thought I was set with arcade stuff, now I am at the foot of an oscilloscope mountain). Still, another cool gadget.

Awbacon - my BVM manual says it can go from 0.3 to 4Vp-p. But I thought TTL goes to 5v, so not sure if this extra volt would take it over the edge (or I am misreading how the measurements work).
 
Joe said:
Thanks SD / Awbacon - just when I thought I was out, they pull me back in (i.e. I thought I was set with arcade stuff, now I am at the foot of an oscilloscope mountain). Still, another cool gadget.

Awbacon - my BVM manual says it can go from 0.3 to 4Vp-p. But I thought TTL goes to 5v, so not sure if this extra volt would take it over the edge (or I am misreading how the measurements work).
Click to expand...
Operative word "goes to"...but like I said, not a one size fits every pcb answer :)

the easiest thing is just to pull the signal down on whatever cable you use to go from the supergun to the PVM. Then you 100% know it won't be over
 
awbacon1 said:
Operative word "goes to"...but like I said, not a one size fits every pcb answer :)

the easiest thing is just to pull the signal down on whatever cable you use to go from the supergun to the PVM. Then you 100% know it won't be over
Click to expand...
Thanks - yes, that may be where I am heading, to be safe. I have however spent the last couple of late evenings learning about all things oscilloscope, just to tame this beast of curiosity.

I blame everyone on this thread for forcing me to consider investing in new gadgets :) "why have two inputs on the oscilloscope when you can pay a little more and get 4", "yes you will never use most of those functions, but all the patterns on the screen look so nice!"...my inner voice is telling me :). If I could travel back in time I would politely suggest to JAMMA that they just invent HDMI.
 
Joe said:
Thanks - yes, that may be where I am heading, to be safe. I have however spent the last couple of late evenings learning about all things oscilloscope, just to tame this beast of curiosity.

I blame everyone on this thread for forcing me to consider investing in new gadgets :) "why have two inputs on the oscilloscope when you can pay a little more and get 4", "yes you will never use most of those functions, but all the patterns on the screen look so nice!"...my inner voice is telling me :). If I could travel back in time I would politely suggest to JAMMA that they just invent HDMI.
Click to expand...
Lol you shop for electronics equipment like I do

a scope is on my shopping list this year
 
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Hope you are all well. I finally got round to testing (playing with?) the new oscilloscope (which I will henceforth call a 'scope' to make it sound like I know what I'm doing). Tested a consolised MVS using BNC connectors (RGB and sync) with 75 ohm in line terminators. Had Metal Slug playing. Instead of the beautiful, clean square wave signals I expected (e.g. like on RetroRGB videos), I got these:

A spaghetti mess of lines smeared across the scope's screen, bouncing around all over the place. i did - I think - manage to measure peak-to-peak voltages of maximum 690mv for RGB and 1v for sync by activating the Measure function. Anyone care to offer suggestions or thoughts? Is this normal?
 

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That's the nature of analog rgb signals. They aren't all the same. Unless there is a specific problem you are trying to diagnose, don't worry about it.

I've had no issues just using an analog volt meter for testing rgb voltage. Just put a white image on-screen (if one is available on a CRT test menu).

Then, the RGB voltage should be around 0.7v for consumer monitors or TVs (like your BVM). You'll find it listed in the manual too. RGB from arcade PCBs is usually 3v-5v. It should be straight forward to check if your resistors are functioning as they should.

You'll find some variation between PCBs so test a few if possible. One thing I wish I had on my supergun were pots instead to allow some adjustment for different monitors (of different ages).
 
arcade stuff is very questionable in comparison to broadcast monitors or other fussy displays.
sync signals especially - not just the voltage but the timings arent always what they should be.

i can see this - i own a tektronix vectorscope, but that doesnt fix it - it just shows me :)
https://uk.tek.com/datasheet/wvr500
 
The signal is analogue and rapidly changing... It's fine! Your peak to peak voltage is also fine, nothing to worry about.
If you want to see a digital (-ish) signal you can use the scope on the sync signal. Try to lock on to the horizontal signal, it should be closer to what you expected.
 
Thanks @Zebra / @stj / @ic3b4ll - I appreciate the swift responses and reassurance! It is indeed a journey of discovery. I can't ever remember worrying about this sort of thing when I was a kid with just one TV, one mega drive and one game - and one composite cable to connect them all. A simpler life. Watched Tenet last night (good film) - might just try and send the scope back in time to see if my young self thinks I am as crazy worrying about signal voltage :)
 
Joe said:
Thanks @Zebra / @stj / @ic3b4ll - I appreciate the swift responses and reassurance! It is indeed a journey of discovery. I can't ever remember worrying about this sort of thing when I was a kid with just one TV, one mega drive and one game - and one composite cable to connect them all. A simpler life. Watched Tenet last night (good film) - might just try and send the scope back in time to see if my young self thinks I am as crazy worrying about signal voltage :)
Click to expand...

If you're using a supergun you shouldn't have to worry about voltage as that is one of their primary functions.

Plus, pro monitors often have over-load protection or warnings built in. If I feed my Ikegami an overly bright image the warning light comes on to remind me to turn down the brightness and contrast.

If you have a game with "dirty sync" some Sony monitors have trouble and you'll require a sync cleaner. These are cheap so no big deal. If they are needed, you likely won't get an image at all until one is installed.

Some monitors and CRT TVs can't handle PCBs with particularly unusual refresh rates (like R-type and Mortal Kombat). Nothing you can do about that. I've only ever had that issue myself on CRT TVs though.
 
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@Joe if you're really in Tokyo then a CRT TV should be relatively straightforward to use. You can use the JP21 connector for true RGB. My experience using SCART is that CRT TVs accept pretty much everything you throw at them IF you use RGB.
 
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Rgb is just a color space. If a TV can't handle 57hz or 54hz games etc then it doesn't matter if you use rgb, component or composite video, it still won't work.

Similarly, using RGB won't prevent an overload if you connect a PCB directly to a TV without going through a supergun (or cable with resisters) unless the TV can handle ttl.

The late model Sony CRT TVs are particularly fussy with refresh rates that aren't close to 60hz or 50hz. That was one of the reasons I stopped using a TV and got a bunch of arcade monitors.

With that said, most arcade games should work on most decent CRT TVs (aside from Trinitron Wega). Unless a person intends to buy one of the few really unusual (for refresh rates) PCBs I wouldn't worry.

I grew up in the UK using a supergun on various CRT TVs and most PCBs worked on every TV I owned.
 
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