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trm View Drop Down
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    Posted: 11 Sep 2010 at 2:07pm
Ok, it's pretty clear that people want the video probe write-up. That will be done this w/e once I've finished digging up my brother's kitchen floor (don't ask).

Sir Gaylord Paul wants the 1084 h-sync adjustment.

So what else? Give us some kind of prioritising and we'll see what we can do.

Cheers
Tim    

ETA: Marked off completed items.


Edited by trmatthe - 09 Jan 2011 at 1:20pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Setch Quote  Post ReplyReply Direct Link To This Post Posted: 11 Sep 2010 at 6:17pm
Hi Tim
 
Some basic tech guides on using scopes & logic probes would be nice :)
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: 11 Sep 2010 at 10:19pm
probes then scopes thou eh?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DanP Quote  Post ReplyReply Direct Link To This Post Posted: 13 Sep 2010 at 10:16am
Good topic Tim,
 
Articles I'd like to see;
 
Basic introduction to microprocessor based video games
Intermediate guide to microprocessor based video games
Advanced guide to microprocessor based video games
Inside the z80 video games (with an example - say Galaxian or Pac Man)
Soldering for dummies
DeSoldering for dummies
Basic monitor removal and disassembly guide (safely!)
Basic arcade hackery introduction
How to diagnose and repair analog power supplies
How to diagnose and repair switched mode power supplies
 
That's all I can think of for now
 
Dan
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Post Options Post Options   Thanks (0) Thanks(0)   Quote andyman Quote  Post ReplyReply Direct Link To This Post Posted: 13 Sep 2010 at 4:20pm
And next week, when you have finished Dan's list, something pcb sound generation/amplification related Wink

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Post Options Post Options   Thanks (0) Thanks(0)   Quote DanP Quote  Post ReplyReply Direct Link To This Post Posted: 13 Sep 2010 at 4:44pm
Originally posted by andyman andyman wrote:

And next week, when you have finished Dan's list, something pcb sound generation/amplification related Wink

Andy.
 
Hehe, I wasn't for one minute suggesting Tim write all this.   I'm hoping that other users will pitch in and write articles for the benefit of all of us if they have the knowledge to do so     Perhaps I'm being naive though...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote trm Quote  Post ReplyReply Direct Link To This Post Posted: 13 Sep 2010 at 5:11pm
Originally posted by andyman andyman wrote:

something pcb sound generation/amplification related 


Sound? That's the easiest part ever to fix and surely doesn't need a doc

It's either the op-amps, the serial DAC (YM3012 or YM3014?), caps in the bypass filter stage around the op-amps, no +12 or a fried power-amp. There you go, doc written .
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Post Options Post Options   Thanks (0) Thanks(0)   Quote guddler Quote  Post ReplyReply Direct Link To This Post Posted: 13 Sep 2010 at 5:24pm
Incidentally, I hope he won't mind the shameless plug but Pobster has already done some of this...


Just a couple of selections from the more general:

There's a whole bunch of useful stuff in there so please do him the courtesy of visiting his main site rather than just jumping into the bit's I've highlighted alone.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote andyman Quote  Post ReplyReply Direct Link To This Post Posted: 13 Sep 2010 at 6:27pm
Originally posted by trmatthe trmatthe wrote:

Originally posted by andyman andyman wrote:

something pcb sound generation/amplification related 


Sound? That's the easiest part ever to fix and surely doesn't need a doc

It's either the op-amps, the serial DAC (YM3012 or YM3014?), caps in the bypass filter stage around the op-amps, no +12 or a fried power-amp. There you go, doc written .


To lots of people here, its easy. To new members, its one of the most common issues so maybe saving the 'My XXX has no sound, what's wrong' question. Thanks for the queue jump Tongue

@Dan, Tim can cope. Probably done them all by now anyway !

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Post Options Post Options   Thanks (0) Thanks(0)   Quote cools Quote  Post ReplyReply Direct Link To This Post Posted: 13 Sep 2010 at 8:45pm
I've got a Funky Jet with no sound so I'd like that article too :)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote trm Quote  Post ReplyReply Direct Link To This Post Posted: 01 Oct 2010 at 12:06pm
Just to get your juices flowing, my recent time sink has almost finished which means I'll soon be ready to get what remains of my 1000 monkeys out of the garage and set them to work. I've only got 2 keyboards but I think they'll take it in turns to type how to fix XXX and then pass the keyboard to the next monkey. I read it on wikipedia.

Only it's been a bit quiet in there since the weather turned. In an entirely unrelated question, does anybody know if it's safe to eat animals that have died naturally?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JohnBud Quote  Post ReplyReply Direct Link To This Post Posted: 01 Oct 2010 at 5:58pm
depends on why they died. if they for example died because they head butted an astra at 70mph, then yes its fine to eat it. however if they died of a disease, then thats a bit dodgy. there was an issue years ago over rabbits. they all had meximatossis, or there abouts, the tell tale sign was rabbits running into trees etc. they first went blind then died, this could pass on to humans. the only quick way to tell was theyre eyes all clouded. then of course you have rabies, these mothers would jump through fire to get at you. but weirdly enough they are scared of water. then of course there is feline entilitous ??? the cat equivilent of aids. so to answer is it safe to eat dead animals you have found. no not unless you are skint and cant afford the real stuff, however if you were a vet then you could probably tell from the brain and innards. and remember the meat could also be rotting. this is the main reason we eat curries today, to hide the taste of rotting meat. im sure we could have a whip round and send you a food basket. or have you went all "man the hairy hunter" ??? please do tell Big smile  my money is on the later as i know you like to shoot things. could it be a stray clay thing has killed an innocent animal. or are you getting ready for the best natural kill ??? blunderbuss at 10 yards LOL if its an old chicken boil it LOL but we gotts to know why you want to eat dead animals you have found.  cheers.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote trm Quote  Post ReplyReply Direct Link To This Post Posted: 01 Oct 2010 at 6:17pm
It was a joke about the fact I've been very busy recently and so the alleged 1000 monkeys in my garage might have died as it's gone very quiet LOL

I think I'll leave mine and your response here for a couple of days so people can catch up and not think WTF and then move them into a new thread in Off Topic Big smile
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Post Options Post Options   Thanks (0) Thanks(0)   Quote guddler Quote  Post ReplyReply Direct Link To This Post Posted: 01 Oct 2010 at 9:43pm
Too late - I already thought that!!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jodo Quote  Post ReplyReply Direct Link To This Post Posted: 01 Oct 2010 at 10:52pm
+1 for a "Basic monitor removal and disassembly guide (safely!)"
 
...but I suggest (if it's workable - seriously) that this and any other guide where approprite, includes a make / model type 'You will need...' tool list. The instructions may be sound but then if somebody goes and substitutes a particular tool due to excitement / eagerness they could kill the board / the monitor / themselves Dead If they buy the same tools and do exactly what the guide says hopefully they will replicate it's success Clap
 
Just a thought Smile
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote trm Quote  Post ReplyReply Direct Link To This Post Posted: 12 Oct 2010 at 3:55pm
Hi Jodo. I'm afraid somebody else will need to volunteer (or be coerced) into writing the monitor related stuff as I have very little knowledge there. I don't mind playing with low voltages but my life expectancy when working on monitors is probably measured in seconds

In other news I've almost done the video probe article - I got some time at the weekend so just need to 'shop the photos and it'll be uploaded. Which one is next in everybody's priority list?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote paulcan69 Quote  Post ReplyReply Direct Link To This Post Posted: 12 Oct 2010 at 5:33pm

Even though for my own greedy cause I'd love the h-sync adjustment mod for my Commodore 1084 monitor first, but...

I would love just as much for the "logic probe for total r-tards" and I think others would be with me on this.

This must include pics or video (video would be better) and step by step of a game running and prob-n' first a z80 and/or 68000 also a ram or two and then an eprom or two and some 74 series logic chips, with what to expect from a faulty chip and a worker so we/I can see what it looks like to have a fault, + compare it to the datasheet as you do it so we can see what does what as you probe it. Be nice to see the in game fault and when it fixes it, i.e a repair from start to finish.

There is a bit of this on you tube, but it doesn't really show why.
Also what the various legs your prob-n' do, and why you would get a hi or low and pulse etc... from that leg? Doesn't have to be loads of info but as the name suggests just a guide.

(And a brief guide to hi and low for tards like me who get very bored by reading pages of code and who just want to see it in action before they learn the theory of it)

I don't think this has been done anywhere else yet and would be invaluable to people like myself who can do the very basics, yet want to take the next step in learning how to fault find instead of ripping bits in/out to make faults disappear.

(Which is what we all do to modern day pc's) We try known good bits until the fault goes then just replace the part, it's the same in the motor trade which I'm in, old skool mechanics don't exsist anymore.
Fault finding in general seems to be dying these days, but for anyone to keep these older and more rarer boards in operation we need to know this stuff to stand a chance.
 
I'm happy to help however I can? Maybe typing something up, or messing with some pics or general find "XYZ" on the net and send it to ya, anything that may take the load off?
Thanks,  


Edited by paulcan69 - 12 Oct 2010 at 5:44pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote karlcdoe Quote  Post ReplyReply Direct Link To This Post Posted: 13 Oct 2010 at 1:59am
Anything on board level repairs is always good. I still have woeful test kit and even the logic probe and comparitor rarely find dead chips (or at least not the way I use 'em) so I suspect I'm not reading them right :-)

Old repair logs (not scientific I know) such as fault X was fixed by replacing chip Y may be specific to one game/platform but I always find them super helpful and cut down on shotgun replacements. In fact, I can never find much like this for Atari System 2 games which is a pain....

I think there are some good guides out there already for XY monitors and raster monitors in general since in the worst case scenario you can leach some TV repair guides or something; and basically most things involving monitors or PSUs can be fudged with a voltmeter and some dutch courage.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote guddler Quote  Post ReplyReply Direct Link To This Post Posted: 13 Oct 2010 at 12:02pm
@Paul: One of the problems with a tutorial on logic probes is that it's difficult to do much beyond the absolute basics, which can be summarised in a sentence or two, thus:

--------
Attach the black lead to GND, the red lead to +5V (usually, check the instructions for the probe), then touch the tip of the probe on a chip leg that is within the range of the probe (getting vague already!). Your probe will have 2 or 3 lights, usually three. One for LOW, one for HIGH and one for FLOATING. They light up according to what the signal is doing. Some probes have a switch that holds that signal, like a "one-shot".
---------

Getting much beyond that get's very vague as you have to know the circuit. It's no good just pointing the pin at the leg of a logic chip and saying, "oh look, it's just HIGH (or LOW)". That's not enough. You need to know the circuit and consider why is it that way? Is it a ground? Is it a supply rail? If it's an input or an output, is it tied to GND or +5? If so, is it by design, or is it because of a fault? If it's because of a fault, is it a fault with that IC, or because of a fault further up or down the line?

If you're not getting what you would consider a reasonable readout, why? Is it again, because of a fault? Is it because the signal is out of spec. for the probe (maybe it's a clock signal and it's out of range)?

Then, once you've got to the point your probe appears to be giving you good data, you're still quite likely (but not necessarily) in the realms of uncertainty for a number of reasons, all of which will require better / further / more expensive kit.

1. Is the signal clean enough? - Will require a scope to view the signal.
2. Is the signal swinging between the two logic states sufficiently? - Will require a scope again.
3. Ok, maybe the signal is pulsing. Is it pulsing with the correct data, and / or at the correct times?

Item three can take a number of further forms: 

1. Depending on what the circuit is for, you could hit it with a logic analyser. These aren't cheap and require a much deeper understanding of the circuit than most of us will ever need.
2. You could employ something like a Fluke 9010 or 9100. These are very expensive (usually) but can be used with less knowledge. Less knowledge is dangerous though, you can easily spend a lot of time barking up the wrong tree here.
3. If it's a timing circuit, a scope could be your friend here as well.

SO, in summary, as you see, a tutorial on logic probes is going to be very difficult to provide in any kind of useful way without it being a much bigger, all consuming masterclass on board level theory, design(?) and repair. Something that I don't believe any of us are really qualified to give. Save maybe 1 or 2 (not me!).

Incidentally, a lot of the things I've talked about here are probably also valid reasons why someone such as Karl are also saying that they rarely find dead chips with the logic probe alone.

I know it's frustrating. I've been there myself, it feels like it's some secret society and the members are doing their utmost to keep new initiates out. Sadly, I can assure you that's not the case. There's just no substitute to immersing yourself in a particular hardware, studying the schematics and really understanding how it works - pick an early and straight forward one for goodness sakes!

Galaxian is always touted as a good place to start. Not specifically because it's easy. There are parts of it that aren't particularly easy, but because they are plentiful, they mostly use standard theory and standard parts and they are VERY well documented. With troubleshooting guides, theory of operation, plus a whole bunch of hobby sites with seriously good information. Mike Coates (Macro)'s website for instance: http://www.arcades.plus.com/

Hope that's gone some way towards demystifying why there isn't a wealth of information on logic probes!


Edited by guddler - 13 Oct 2010 at 12:02pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JohnBud Quote  Post ReplyReply Direct Link To This Post Posted: 13 Oct 2010 at 8:03pm
it would be nice to know the very basics of fault finding. right all the way back to switching on. i think that is the base for repairing things. i would like to know how to test for an rgb signal, and how do the guys on otaku get the screen with a grid onto the monitor. most of these very basic things are a mystery to the complete noob. even down to the, is the fuse in the plug ok. a lot of people are really lost when it comes to cabs, and faults. methinks a very basic fault finding type flow chart with a couple of pictures would be great.  cheers.

john bud
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