Video probe tutorial - discussion thread

[trm]

Hi. This thread is for asking any questions about the Video Probe How-To:

http://www.ukvac.com/forum/forum_posts.asp?TID=328679&title=how-to-build-and-use-a-video-probe

Due to the urgency of this request the article isn't 100% polished so I'll be revisiting it shortly but there is enough there to allow somebody to build and start using the probe.

All input is very welcome!

cheers

tim

 

[trm]

Just as a quick FYI - I normally start off with the Red, Blue & Sync lines enabled in pass-thru mode. This way, anything you probe will be overlaid on the screen in green. If you want a clearer picture of what the probe is seeing then use the cut-off options for the Red & Blue. There isn't much point (yet) in cutting-off the Sync line as this will cause the monitor to lose sync.

Interesting points to probe are multiplexers/de-muxes near GFX roms, any part of the video bus, any ICs around the video output stage etc; basically anything which might have graphics data flowing through it.

In addition, you will start to recognise what specific busses look like when they're "healthy" - a crosshatch pattern represents a very fast changing signal, whereas solid bands of green and black on the screen show a signal that's switching quite slowly - when you see green, the logic level is high and when you see black, logic is low. Try probing the address or data lines on a CPU.

The followup article is almost complete and includes a worked example of monitoring the latter video stages of an Atari board showing how the probe can be used to determine what's transiting the video bus and where any faults may be introduced.

cheers

tim

 

[DanP]

Tim, great post and something I will definatley want to build asap. I might try and adapt this do I can create a video probe module for my test rig. If I do manage it I'll post some pix.

DanDanP2011-01-11 11:48:23

 

[trm]

As I mention in the article as soon as I have some time I'll be posting part 2 which includes some demonstrations of use. The how-to isn't as polished as I'd prefer but people have been waiting a while so I figured it was better than nothing!

 

[andyman]

That's pretty cool Tim, may have to build one, looks handy. Have a week of arcade related goodness coming up due to my not having a Christmas holiday.

Hope you now have a grommet on the cable exit from your box in t'other thread though

Andy.

 

[trm]

That's pretty cool Tim, may have to build one, looks handy. Have a week of arcade related goodness coming up due to my not having a Christmas holiday.

Hope you now have a grommet on the cable exit from your box in t'other thread though

Cheers dude I do indeed have a grommet for the cable entry points, but I keep meaning to fit them when I fit the resistor on the vid probe

.

Enjoy your hols - part 2 is coming soon which shows the probe in use and reveals quite how useful it is. Then it's a case of working down the tech articles wish list

 

[paulcan69]

Dude's, just because I've never dealt with them, I want to use my multimeter leads as my green channel lead to probe when using my video probe I'm about to build.

I have all the things I need except the banana socket.

Are those 4mm banana sockets what I need?

I want the socket to be the same as the socket on a multimeter, are these the same thing?

Many thanks dude's and please hurry I want to order one now so this weekend I can get it all built.

Ta

 

[trm]

Hi dude,

I don't know what your test probes are like as there generally isn't a standard

I'd say if you're getting some parts from Maplin then buy http://www.maplin.co.uk/moulded-4mm-test-probe-leads-5665 (part num HF33L) which are 4mm connector probes. You get a pair and only need one, but it's only £4

The other aspect is some test meter probes have a shielding plastic cylinder that goes into the meter socket which stops any point of the test probe being touchable so that can bugger things up too.

Things are a bit busy at the moment but hopefully I'll be able to finish off part 2 at the weekend so you've got a tutorial on how to use this.

cheers

tim

PS Not sure I understand the bit about "never dealt with them"?

trmatthe2011-01-25 20:59:07

 

[paulcan69]

Cool, even better I've got those now,

Ordered leads + socket.

Thanks Tim.

P.S yeah I wasn't very clear, I mean't I've never used those multimeter style sockets before, I've never had to.

 

[paulcan69]

Right done it!

I'm round the in-laws right now and unable to check and test it, but done!

Using an old Gateway P3 500MHz case, that this old lady gave me when her computer died and I built her one out of old sh*ty bits (free of charge of course - bless her.)

Here's the beast, not the best looking thing I know but it houses the Jamma switcher, a bundle of controls so later I can hook up player 2, and my new switches and probe socket!

Can't wait to try it now, can anyone recommend a exact chip and leg to "probe" when I get home so I can try it and see an image on the screen please?

Thanks Tim for the diagram, at least you've made one person happy!

Ta.

Paul

paulcan692011-01-30 16:50:10

 

[trm]

Awesome! I'm in a major rush, but look for things like multiplexers (try googling for 74 series multiplexers/demultiplexers to get some chip numbers), latches such as LS374 around any obvious video part of the circuit, gfx ROM outputs and anything connected. The best way to get a hand on this is to probe anything and everything - I've not broken anything by probing away at random, but I wouldn't go poking the 12V feed

Not only do you get to see gfx data, but you'll also see timing signals which is another useful part of the probe - these will generally look like stripy bars of different sizes or a cross-hatch pattern on the screen - try some of the CPU address/data bus pins too.

Will try to get back later to add some more, but basically probe away!

I'm very close to having the "using" part of the post ready but it just needs some better pix.

 

[paulcan69]

Right tested it and it works lovely, at first I had no green but then discovered I had the spdt switch for the green wired incorrectly, quick swap over and sorted.

Also just a question, I only had a 470ohm resistor and the probe part works good, a little dim though, if I use a lesser resistor say a 260ohm would it be brighter??

If that's not how it works then I shall just turn the brightness up whilst I'm probe'n!

Ta.

(Tim also thanks for your reply about my logic probe, good shout I'll stick with the one I have and hunt down a Fluke)

paulcan692011-01-30 23:02:59

 

[trm]

Drop the resistor value. I'll get some pics up now that tax time is out of the way to give you an idea of how bright mine is.

As for Fluke, have a squiz at the manuals I suggested to see if you've got the time to read them a few times through (as I promise it's the only way to get the 'hidden' 80% of the functionality) and then we'll discuss further guvnor

ps Now that I've got all my accounts sorted then I'll be increasing my work rate.

 

[paulcan69]

Sorry on a slight side note, which Fluke 9010A manual, there's like 5!!!

I'm looking at the service manual (provides specs, theory) or should I get the programming one?

I'm confussed, so many manuals

 

[paulcan69]

Sod it i'll get them all! and have a good look.

Looking at them now, operators first, then programming, cheers.

 

[guddler]

There's a roadmap at the beginning of each manual that tells you where you are in the order in which you're meant to learn (I think!)

Forget the service manual for now.

 

[paulcan69]

Cheers Guddler will have a good look, ta

P.S Your website is down?
paulcan692011-01-31 00:59:39

 

[guddler]

Working for me...

 

[favouredson]

Working for me...

Check the link in your sig, Martin.

It's a feed:// link rather than an http:// one.

I would assume it works if you are a subscriber but, as I don't bother with rss feeds, I can't say for sure.

You can view it if you replace feed with http but clicking the link, for me and Paul at least, doesn't work.

 

[trm]

Paul - The link is meant to be an RSS feed (I'm assuming that given it's labelled as an RSS feed). It works for me, apart from wanting to fire up Outlook instead of auto-adding to my Chrome RSS reader.

If I change it to an http call as Garry suggests then Chrome will show me the expected RSS sub details. I wonder if it works as-is in Safari