How To Find Faults With The Test Eprom - 1977 Williams Lucky Seven Pinball Machine PCB Repair
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- เผยแพร่เมื่อ 10 ก.ย. 2024
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This machine sure is a Lucky 7. ….lucky to find Ronnie who don’t take no for an answer. Outstanding!
I love to see you pull our your meters and check traces and troubleshoot. I worked on circuit boards for years for IBM before I went into IT, and I miss doing that. I have some stuff laying around my house that needs fixing. You are inspiring me to make some more "Can I Fix It?" videos. Have a good one!
I'm repairing my first table. A laser Ball. These videos are invaluble. Thank you for the work you do and letting us learn from you!
Good video Ron. While I have not done a lot of electronics, I have been working in marine electrical for almost 40 years. And in troubleshooting, I do call that process of finding the fault “chasing the rabbit”. Sometimes you catch it easily, but then another time the rabbit will do an NFL football move on you and you almost can’t catch it😂.
After all the years of doing this, I have to say that finally finding the problem after it has soundly whipped your ass is one of the most enjoyable parts of doing the work, to be able to say “you had me on the ropes, but you didn’t beat me”.
Anyway, I have always enjoyed your videos, and watching you do your thing has certainly made me want to explore the electronics part a little more than I have been. Thanks for sharing how you do it, and if you ever decided to write a book on electronics troubleshooting, I would certainly order it! Thanks again, hope you will be making these videos for many years to come. John Cantrell.
Thank you John! I may write a book one of these days on some of my thoughts on how we repair things. Sometimes I get mad at the boards and say "I'm the only one who's even tried to help you in 40 years, and now you want to fight!"
Another great video from Dr. Frank-ron-stein 😀
EXCELLENT video. Thank you so much for putting this out into the world. You are a gift.
Don't be humble Ron. You're at the point in your career where you can make any of these old suckers boot! Man I love these videos!
I forgot to post on the last video. My machines at work years back had Mallory capacitors in them, the logo brought me right back. HUGE caps too, for the motors (1/3 HP each) I don't remember the rating, they were BIG tho. Maybe 2k "MICRO FARAD" as a guess? Some REDONK number lol, and thanks Ronnie, I can NOT say microfarad normally anymore, only how you do LOL. Good caps tho I must say, in since the factory I'd assume, changed some out over the years but for the most part they held up well! Enjoying the videos as always! :) *Edit* "Samsonite... I was WAY off!" higher voltage caps, not crazy crazy rating of "MICRO FARAD", saw some different ratings, seems like 120V 462-550 "MICRO FARAD" is preferred by techs I know are GOOD ones lol, I think the voltage ratings are a bit upped from stock (looking thru parts manuals lol) but they seem to work well for the guys I know, mainly they just give the motor a "kick" at start and aid in the braking as well. Okay, just once more... MICRO FARAD. Done. Thanks again for the content! :)
I have tried gaming chairs. I did not like them and they broke less than a year after purchase. I switched to a Serta Icomfort 5000 and have not looked back. It stays comfortable after hours of gaming and reclines for naps if needed. The added bonus of a wide top has made the furrbuts happy as they have a place to nap while I game.
Thanks for the cool info Ron, especially on the test ROMS & other valuable tidbits.
Remember these old 8T28 tristate bus transceivers which would die on me a lot but I believe 74LS241 are equivalent with some mods.
Good move to jump the old chips as newer EPROMS & RAM devices are far less power hungry so fanout isn't a huge issue, like you mentioned.
The gaming chair looks amazing & it's been so long since I've seen such a well made chair & kudos to E-win for offering such a nice, sturdy well built office chair.
Stay awesome!
You had me at "Found you, sucka" 😅
What's goin' on Jabo!
The 8T28 is basically a 74LS241 with 4 data T/R pins connected internally and double the output Low drive current at 40ma.
There's a limit to how many outputs a logic can drive. To protect the expensive CPU they would buffer the address and data lines because they had so many loads.
Yeah, fanout current.
IS that why those buffers were there? That's good to know. I didn't know why if you can just bypass them, they were there in the first place. A couple bucks of extra parts in the day, and extra complexity. I guess the current isn't exceeding what the CPU can provide afterall??
@@SteveJones172pilot -- Yes, they often add buffer chips to act like an amplifier to increase the fanout current and allow more things to be driven.
And there are other "extra" chips on boards. The many decoder chips that vintage systems used with the memory are an example. Those chips were used to be able to use smaller denominations of memory than there were address lines and still use all the addresses. For instance, in a 64K system, let's say you only have 8K chips. That would be 13 out of 16 address lines. So for the upper 3 lines, you add a 3-to-8-line decoder chip (the inverting variant). Then what they do is wire all the data and address lines in parallel but connect the /CS line of each chip to an output from the line decoder. Thus only 1 chip is actually on the bus at once, despite being wired in parallel.
Speaking of line decoders, the largest ones made are 4-to-16. What if you need a 5-to-32? In that case, you'd use 2 4-to-16 decoders and an inverter. The line decoders have /CS lines too. So in this case, you'd wire the inputs of the 2 decoders in parallel, and connect all the outputs to different RAM chips as before. And what you do about the highest address line is to wire that directly to the /CS of the low bank's decoder and wire it through an inverter to the high decoder.
Id love to be able to learn this kind of stuff..not like i haven't tried before just doesnt sink in...
deciphering what the original designer/engineer did and the reason/logic behind it always fun. the rabbit hole never seems to end till that ah ha moment, simple problem makes itself apparent. now that you know where to look, one more nugget of troubleshooting knowledge to utilize
Remember the song “Even the Losers (I suck at pinball), get “Lucky” Sometimes?”
The 8t28 appears to be a non-inverting three state quad transceiver.
I have understood that the "three state" part means that it can drive its outputs high or low, or let them float, this would be necessary in some more complex boards where more than one device can make requests on the same bus, so that one device, when inactive, isn't driving the bus lines high or low when another one tries to set them.
The Motorola datasheets that I found are seemingly at a very poor quality (probably I, an non-paying passer-by, am not getting the full resolution images). But from them I have gleaned that the chip has four throughput channels, all of which have a receiver input, a driver input, and a bus output. Apparently the driver pin, when set, forces the respective bus output to the state of the respective receiver input.
Now this scheme that we see here, appears to wire the receiver and driver pins of each channel together so that at one level of input the output is forced active, and at the other it is set floating. The chip operates kinda like a current amplifier in this mode. With a lot of ROM/RAM etc connected the processor alone may not be able to consistently pull the bus lines low enough, so the buffer is put there to do the hard work as it can sink or supply much more current.
You could possibly do the same with AND gates on some boards, but you would lose the option of "floating" inactive state so on other boards where multiple devices might access the bus independently, it might not be a good idea.
With modern ROMs/RAMs you don't necessarily need buffering because they require much less current to pull their inputs low and the CPU can handle them directly, so you can just remove the buffer chips and jump the gaps.
That makes sense! Apparently the original proms were hungry, and even a lowly 2716 eprom was 'modern' enough that they didn't need the 8t28. They actually designed them out of the board once they got to system 6 (they skipped system 5)
@@LyonsArcade The 6800 itself is a three state device, so optimally with a low current memory it could directly work with other three state devices on the bus on a more complex board. I read its limit is about 0,2mA, so if more current must be sunk form the bus to pull the lines low, a buffer is needed. All possible pullup resistors, and all devices that internally pull their lines up in inactive state, add to the current that needs to be sunk to get the lines low.
To fit onto the same bus a chip that does not itself have three state functionality, buffering would be necessary, and this scheme would be one possibility.
That's a sweet chair joe!!! I got to get me one!😂
The missing bottom segment on the master display indicates it's the segment signal not getting through most likely, not the display itself.
I wish they would release a video game with all of the old pinball machines because they don't have any game with old gottlieb, bally, stern, Williams tables.
I have to give to you guy👍👍👍👍
What's goin' on Harry!
@@LyonsArcade all good… how about guys😎
I noticed your sponsor of Ewin. This isn't an issue with me, and I find this product interesting as something that I may purchase. Could you guys provide a direct link to the sponsor or an Amazon affiliate link? If I do purchase this product, I would like to give credit where credit is due. Also, I would like to note that normally that I'm here for the content, but I did find this product peak my interest.
Can you explain how to determine where to connect a logic probe to no matter the game or board
This seems like what's going on with my World Cup. I've always known that I need to replace the sockets. Just haven't done it yet.
howdy u-all
So now you got a back hernia the chair?
JOE CLASSIC< Why not just replace the bad 8T28 Buffers chips with brand new 8T28 chips or 74LS367? because leaving out the buffer IC chips makes the logic signals levels noises and current is low, the buffer chips boost the current levels and cleans up the signals plus if there are short circuits it won't damage the CPU 6800 or Z80 chip data lines or address lines. I think you mentioned even if you replaced the 8T28 Buffers chips that they won't work with certain RAM chips because the Bigger Sized RAM chips will "conflict" or cause Errors with the 8T2B buffer chips? Correct me if I'm wrong but I think that is what you mentioned
I would be curious as well.
Test Eprom
Why bother taking the 8T28s out? Why not just short the pins and leave them in, they're not going to affect anything with the inputs and outputs shorted together. Are they?
Good question! The only thing would be, any chip has an internal connection to +5 and ground, so you always have the possibility of if it fails, it shorts itself to ground or 5, if the chip is removed that can't possibly happen. You would probably 95% of the time be completely fine for years and years leaving the chip in though so I wouldn't have a problem with people doing that personally.
Ron is absolutely correct. If you aren't using a part, remove it as it can still cause problems if/when it fails as it remains connected to your power rails an even to the signal pins. That said, I'd think a buffer/driver has the benefit, even if not explicitly required, to protect the more valuable CPU if something down the line fails.
@@LyonsArcade I was wondering about that and thinking you could just cut the 5 volt pin, and maybe the ground pin...
Thinking about it a little more I've realized that you wouldn't have to de-solder the chip, just cut the legs off -- which I'm pretty sure is what you said in the video -- I was picturing having to de-solder the chip -- so it makes total sense to just cut it off.
Yodelayheehoo
My issue with those pleather chairs. They make my ass sweat and the pleather wears out very quickly as do the cushions. I like mesh chairs.
I thought Aztec was the first Williams solid state.
It was a prototype, that's like saying that when they designed the first board that was the first solid state. The first one you could buy was Hot Tip