I have updated first post with some of the myths and their status. Will try to catch up and add some others but if you feel real strong about changing status of one, quote it and post a fact.

The fun ones are fine but too many for me to try and update.
 
re. medium resolution tubes


DVD resolution 720 x 480 which is digital was was displayed on 90's tvs (without moire effect) would require .55mm...kind of jives w/ above. I feel pretty good on this one.

Interlacing



Edit: same way Tapper has a resolution of 512x480 on a cga screen
If Toobin uses a low res tube that seems like a cost saving measure, but i'd have to look up what the game resolution actually is

True that is with interlacing....but 480 progressive is 640 x 480 so still would meet needs.
 
But you can't display 480p on a standard tv!

doh...for some reason I thought s-video was 480p but it is 480i. Will have to rethink this part of my logic but it was flawed anyway as we are dealing with analog vs digital. I did find it interesting that there are a few interlaced games but not many.
 
Myth: Using the 'screwdriver method' to discharge a vector monitor (i.e., with no resistance in-line) will damage it.

Fact: 6100's are self-discharging, so there isn't much charge to discharge to begin with, so it's moot. B/W vectors (G05's and v2000's) have been discharged with screwdrivers by many for years, without a single documented case of damage. (They also self-discharge, but more slowly).

G05s do not self-discharge other than by leakage.
The snapback when you short the HV to ground can damage the HV diode.
 
also CR7000 says unplug the AC cord to the chassis....well if your gnd plug isn't connected to earth where are you discharging this to? This has always bothered me too. in a game, the on/off switch prevents voltage from going to chassis but at least your FG is still connected. Just going to metal frame that isn't gnd'd doesn't make sense.

The potential is built up across the tube... the back of the tube is connected to the frame.

The charge just gets moved from one plate to the other until the voltage is equalized when you short out a cap... it doesn't need to go to "ground".
 
I can't get behind this being a myth for 19" monitors... And people not noticing isn't a good enough reason (for example, some people don't notice scaling, distortion from widescreen, wrong resolution)

Higher rez can be displayed on a lower rez tube, but it'll look like shit.

Look at the difference between an amplifone with medium rez tube and a 6100... there's no inherent resolution -- the sharpness if the image is defined by the dot pitch.
 
here's one or two that bugs me, my myth/truth probably could use some better explanation or wording but..

Myth: if you have a non-working game board, you should replace the caps on the logic board

Truth: replacing caps on the LOGIC board is almost always basically useless, with the rare EXCEPTION of games that have their power supplies on the logic board (pacman, galaxian, mspacman etc) OR if your having issues with a specific sound AND your system uses discrete analog sound circuits rather than a digital sound processor. Furthermore please don't replace the tiny ceramic caps with electrolytics.

---

Myth: fixing boards is rocket science that only geniuses should attempt.
Truth: it's basically the same as car repair or plumbing repair or construction repair, just needs a certain amount of base knowledge, the right tools, a little practice and confidence.
 
G05s do not self-discharge other than by leakage.
The snapback when you short the HV to ground can damage the HV diode.


Agreed about the leakage. However it's enough that it will dissipate faster than other rasters, which can hold charge much longer (in my experience).

What's the theory behind damaging the diode? I'm open to the idea of it being theoretically possible. But I know between folks like gamefixer, myself, and other folks who have worked on a lot of them (comprising many hundreds of discharges), I had never heard of a single confirmed case of a diode being damaged, until the one in this thread (which is a single data point, that could theoretically be explained by other things). And I actually researched it as far back as I could go, searching everything I could find here, and going back to RGVAC as well.

I could be convinced to believe otherwise, but I'd need to see some kind of data, as there is currently more evidence suggesting you're pretty safe doing it, versus requiring resistors.

Here's a thread from two years ago on the topic, for anyone interested:

https://forums.arcade-museum.com/showthread.php?t=377242
 
Myth: if you have a non-working game board, you should replace the caps on the logic board

Truth: replacing caps on the LOGIC board is almost always basically useless, with the rare EXCEPTION of games that have their power supplies on the logic board (pacman, galaxian, mspacman etc) OR if your having issues with a specific sound AND your system uses discrete analog sound circuits rather than a digital sound processor.


I generally agree with this one, and definitely agree for any Atari boards.

However, I've personally come to the opinion that it depends more on the brand of caps (OH NO NOT THIS AGAIN DON'T FREAK OUT EVERYBODY). I say that because I have specifically seen Sea Wolf and Thief boards (two other boards I specialize in) with original factory caps that have measured high ESR and/or out of spec capacitance. However they were Illinois, Capar, and other mid-level and/or lesser known brands. Any Nichicon caps I see on old 80's logic boards are always good, unless physically damaged. (Monitor caps are another story, but we are specifically talking about logic boards here.)

However the exact impact of the out of spec caps I have seen is also debatable, as they are mostly usually just 5V/12V filtering caps, and generally not mission-critical, in terms of a single cap causing an entire game board to not work. So in general I agree with what you are saying, in that a cap kit on a game board is very unlikely to fix any major issue that is causing the board not to work.

This is also one case where it is useful to have an ESR meter for when you aren't sure, and you want to fully check everything on a board (e.g., during a full overhaul/bulletproofing, where you want the board to be good for a long time to come, and you want to make sure everything is healthy, with sufficient margin.)
 
Ultimately it comes down to the amount of current that crosses your heart, which can depend on a lot of factors.

To be more specific:

Current level (in milliamperes) -> Probable effect on human body

1 mA Perception level. Slight tingling sensation. Still dangerous under certain conditions.

5 mA Slight shock felt; not painful but disturbing. Average individual can let go. However, strong involuntary reactions to shocks in this range may lead to injuries.

6-30 mA Painful shock, muscular control is lost. This is called the freezing current or "let-go" range.

50-150 mA Extreme pain, respiratory arrest, severe muscular contractions. Individual cannot let go. Death is possible.

1000-4300 mA Ventricular fibrillation (the rhythmic pumping action of the heart ceases.) Muscular contraction and nerve damage occur. Death is most likely.

10,000 mA Cardiac arrest, severe burns and probable death.
 
here's one or two that bugs me, my myth/truth probably could use some better explanation or wording but..

Myth: if you have a non-working game board, you should replace the caps on the logic board

Truth: replacing caps on the LOGIC board is almost always basically useless, with the rare EXCEPTION of games that have their power supplies on the logic board (pacman, galaxian, mspacman etc) OR if your having issues with a specific sound AND your system uses discrete analog sound circuits rather than a digital sound processor.

I generally agree with this one, and definitely agree for any Atari boards.

However, I've personally come to the opinion that it depends more on the brand of caps (OH NO NOT THIS AGAIN DON'T FREAK OUT EVERYBODY). I say that because I have specifically seen Sea Wolf and Thief boards (two other boards I specialize in) with original factory caps that have measured high ESR and/or out of spec capacitance. However they were Illinois, Capar, and other mid-level and/or lesser known brands. Any Nichicon caps I see on old 80's logic boards are always good, unless physically damaged. (Monitor caps are another story, but we are specifically talking about logic boards here.)

However the exact impact of the out of spec caps I have seen is also debatable, as they are mostly usually just 5V/12V filtering caps, and generally not mission-critical, in terms of a single cap causing an entire game board to not work. So in general I agree with what you are saying, in that a cap kit on a game board is very unlikely to fix any major issue that is causing the board not to work.

This is also one case where it is useful to have an ESR meter for when you aren't sure, and you want to fully check everything on a board (e.g., during a full overhaul/bulletproofing, where you want the board to be good for a long time to come, and you want to make sure everything is healthy, with sufficient margin.)

The other asterisk I would put on this myth are tantalum caps on MCR/Astrocade boards. Failed ones will generally be easy to spot visually (or at least show a short on the line) and in many instances simply replacing them will fix the board. They cause many issues on these sets.
 
Higher rez can be displayed on a lower rez tube, but it'll look like shit.

Look at the difference between an amplifone with medium rez tube and a 6100... there's no inherent resolution -- the sharpness if the image is defined by the dot pitch.

Few additional info points on this debate.

1. Probably need to break this discussion into multiple myths. Calling a "M" designated tube "medium resolution" is inaccurate. I think everyone agrees it stands for "Monitor" and very likely has a higher dot pitch shadow mask than regular "A" or 19V tubes. It is assumed but not 100% proven in all cases.

Myth: There is such a thing as a Medium Resolution Tube.
Fact: M designation stands for Monitor. It implies the tube has a higher dot pitch shadow mask.

2. Dot pitch is one part of the tube that we have think about.
https://www.repairfaq.org/sam/crtfaq.htm#crtcrs << lots of good stuff to read here
"The ability to display fine detail involves many factors including the resolution of the video source, video bandwidth, sharpness of the electron beam(s), and the dot/slot/line pitch (color only) of the CRT. The CRT is primarily responsible for the latter two. The focus or sharpness of the spot or spots that scan across the screen is a function of the design of the electron gun(s) in the CRT and the values of the various voltages which drive them."

from Sencore document.
""Most of today's high-performance CRTs operate at a high negative bias
(typically -100 to -132) and corresponding high G2 voltage (400-600 volts). This produces a very fine, tightly focused electron beam that results in very high resolution."

3.May have to separate Color Vector from original Medium Resolution myth discussion. Not sure how to equate X/Y to standard raster resolution but I think we can all agree it is likely higher than Medium Raster Resolution (512 x 384) possibly approaching 1024 X 768
Sources
https://forums.arcade-museum.com/archive/index.php/t-256126.html >> implies max 1024x1024 via 10bit DAC
http://easymamecab.mameworld.info/html/monitor9.php
says 525 lines (480 active + 45 blanking) x 60 Hz = 31.5 kHz (vector games) <<emulation

So still no empirical data measuring actual dot pitch of many M tubes vs all the A tubes out there but for color vector games I am definitely coming to the side that dot pitch is definitely going to make a difference.

For medium resolution raster games, as stated before, you need .75 dot pitch for 512x384 (medium resolution) We do have examples of this being measured on regular 19" TVs at exactly .75mm. 25" tube would need .99mm so don't think there is any doubt any 25" tube can be used for medium resolution. Still not a lot of emperical data here either but the I am still feeling good on NOT needing a "M" tube to achieve medium resolution.
 
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The other asterisk I would put on this myth are tantalum caps on MCR/Astrocade boards. Failed ones will generally be easy to spot visually (or at least show a short on the line) and in many instances simply replacing them will fix the board. They cause many issues on these sets.


Ah, that's really good stuff. Thanks for posting.

And to add an asterisk to an asterisk to an asterisk (lol), a PCB cap kit would be unlikely to include tantalums (though maybe you could argue they should, however AFAIK they currently mainly include electrolytics). So it's even more unlikely a kit would catch that issue.
 
The other asterisk I would put on this myth are tantalum caps on MCR/Astrocade boards. Failed ones will generally be easy to spot visually (or at least show a short on the line) and in many instances simply replacing them will fix the board. They cause many issues on these sets.

...and midway 8080... but generally you just need to remove the shorted cap, not even replace it...
 
Few additional info points on this debate.
(snip)
Still not a lot of emperical data here either but the I am still feeling good on NOT needing a "M" tube to achieve medium resolution.
Myth: People just want to joke around on KLOV.
Fact: Some people want to have a real discussion.

Let's move the monitor resolution/dot pitch discussion to a new thread so it's easy to follow/discuss: https://forums.arcade-museum.com/showthread.php?t=430689 . :) I've got some info to share.

DogP
 
I had never heard of a single confirmed case of a diode being damaged, until the one in this thread (which is a single data point, that could theoretically be explained by other things).

I can give one more data point on this. I was working on an Asteroids years back and I think I did the same thing. I had just put a brand new diode in the thing. When I tested the monitor it worked good but it had some other problem. I don't remember what it was. But I discharged it and fixed the other problem and put it back. But then the diode was blown and I had to order a new one.

Again, it could be explained by other things. But at the time I remember thinking it was because of how I discharged it. Could be right. Could be wrong.
 
Really interesting info. I'd been wondering about displaying 480p on standard res monitors for a while, I managed to get it working but it looked terrible. What's the max res for a medium res monitor then?

I got one:
MYTH: Ms. Pac-Man is Pac-Man in drag.
FACT: Ms. Pac-Man is Crazy Otto in drag.
 
I can give one more data point on this. I was working on an Asteroids years back and I think I did the same thing. I had just put a brand new diode in the thing. When I tested the monitor it worked good but it had some other problem. I don't remember what it was. But I discharged it and fixed the other problem and put it back. But then the diode was blown and I had to order a new one.

Again, it could be explained by other things. But at the time I remember thinking it was because of how I discharged it. Could be right. Could be wrong.



One thing that isn't widely known about these, is that it often isn't actually the diode that is bad. Most of the time the root cause is actually the springs and contacts, which connect the diode to the wires (which then may or may not cause the diode to fail, but often not.)

One of the main failure modes for these cages (in addition to caps) is that the grease dries out that was used inside the boots, air gets inside them, and the springs rust. It's also partly due to a poor design to begin with, because the leads of the diodes were just bent over and clipped, and the springs just press up against them, touching the diode lead at just a single tiny point of contact.

When the springs rust, that single point of contact begins to go resistive, due to the oxidation. Because of the large voltage present, this generates a lot of heat (even though the current is small), as Power = V^2 / R, (i.e., voltage drop across the load squared, divided by resistance). Because V is so big (12-14kV), even the smallest resistance will end up generating heat.

When heat happens, it causes the spring to rust faster, generating more resistance, more heat, more oxidation, etc. The whole thing snowballs, and the boot eventually burns up. This is why you see most of the boots on these HV cages hard and blackened. (The original ones are soft and transparent).

And if you just replace the diode, you often won't fully fix the problem, as the rusty springs will often easily cause a bad connection again pretty quickly (if not immediately).

In many cases when I refurb these cages, the diode is actually still ok, once you clean it up. I soak the springs in vinegar and then tumble them to remove all of the rust, and clean out the boots and cup-shaped contacts inside the boots with acetone.

Then when I reassemble them, I solder the springs to the diode (see below), to remove the weak link. I also dremel out the cups on the end of the wires, so there is no crud inside them, which gives solid contact between the springs, and the cups they sit in.

In some cases if everything is really burned badly, I'll just cut off the cupped contacts, and solder the diode directly to the wires, and then put the boots back over them (or cover them with black RTV silicone, if the boots are too far gone).

Bottom line - It's important to clean and fix the contact points between the diode and springs (especially if rusted and burned) in order to fix these properly, else you can easily see issues return, even with a brand new diode.


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