I'm playing around with a board, that has some corrosion. Nothing too scary.

I'm also trying to follow the schematics.

I have a couple questions for you guys that know this stuff.

Can someone give me a quick idea of the start up process for the PIA's. This is a 4 flash code. Which is U38. I've changed and socketed the chip, same error. Has power to the chip. So, I'm guessing a corroded trace? Or whatever is in between the during test? What is it testing? And what direction do I look next?

I'm trying to read the schematic and just don't know enough. So, I figured I'd ask here.

Also, I'm just playing around with the board trying to learn it better. If I can get it to boot the whole way, I'll be happy for now. Most of the corrosion is around the battery holder. And I do plan on neutralizing and replacing parts. Was just curious how the start up test works.

Also! Does someone know where to download a full page schematic. I found some but they are pages jumping back and forth. A full page would be so much easier to try to learn from.

Thanks!

Thank you!!

I was looking at the schematic and couldn't understand exactly what was going on there. Or what was needed to communicate(or how) for start up or the initial test(?). You have me in the right direction now! Thanks again!

Luckily! I had some extra PIA's I bought from a guy in Columbus Ohio that ships super fast! Great guy to buy stuff from!! I knew those would come handy one day!!!

Thank you!

I'll check to see if the corrosion made it to the back side of the board.

The test Rom would be great, just kind of limited now and playing around to see if I can get it to work. Something to play with when the house goes to sleep.

I tested the PIA it was working like the others. Except A13 was solid High at U38. It was pulsing at the Rom and the 6802...I'm still looking at the schematic to try to sort that out and see understand if it's supposed to be locked high, or if something somewhere is holding it. The same when the chip is out of socket. I'm not in front of it now but think it was pin 22.

So, I stepped back from that for now, the section to the left of where the battery pack was had a lot of damage. Took everything off that section, sanded,neutralized, and retinned it. Still working on putting that back together. So at least I know that will be solid.

Ok...I just double checked everything listed above....This makes no sense to me....

U13 pin 5 is pulsing
U10,U51,and U54 are pulsing at pin 24....

So...How the heck can pin 22 of U38 be held High? Doesn't that go to all the others too off of the same line(?)?

Then I thought...Well maybe I'm getting mixed up on the probe, and no, the pin is high not dead, It's at 4.9v. Even with the chip out of socket....Wouldn't that corrupt the line and make the others high too if it was shorted to power?

Makes no sense.....I just started trying to look at and understand the schematic again now that I have the other section together. There has to be a chip or something this is running through that is holding/shorting(?) it? Kind of a fun puzzle!

And maybe pin22 of U38 is supposed to be high and not pulsing? I just assumed that might be the problem since the 6802 and other areas of it were pulsing. I'm still trying to learn this stuff.

The 6802 is pulsing, U13 pin 5 is pulsing....I'm now trying to follow the trace backwards seeing where it goes. For me trying to trace the schematic is confusing when they run all of them into one line. It's hard for me to see how it's tracing back.

Looks like...U16,U28,U29 are all on that trace too when trying to follow the trace. I'm trying to match that to the schematic. Trying to figure out where else it's going.

I don't think that is my problem....U38 pin 22 ends up the VCC.? by actually tracing the board. I'm really confused now...... I'm lost....I'm starting over. From the top of the thread.........

I found a trace broken for the IRQ Pin 37 on U38. Fixed the trace.

Now, with the chip in the Diagnostic light flashes really fast, after a minute or so, it lights solid. At that point it seems to lock the board. I can't push the switch and make it reset.

With the U38 out I just get the 4 flashes, over and over.

Thank you!
I'll do that next. From the looks of it I'm not the first to play with this board. So, I'm looking over past repairs now. I found a replaced resistor at R96 where the solder was touching two traces. May not be the related to the problem but I missed that the first look over. So I started over by checking everything that was repaired or for any heavy corrosion. I'll do the check above once I get some things cleaned up on the board.

Thanks again!!!

I did replace the sockets, but I was in a hurry and too excited!! So, I was kind of half hacking things....So...I slowed down. Decided to start over and do it right or as right as I can. It had corrosion and broken traces.

I'm no where near finished but this is where I'm at so far. I know I have more to remove from the board to get all of the corrosion but I kind of jump around when doing things. Eventually, I will get to those areas too. Here are a couple pics. I plan on re-tining traces. And yes, I know it would be easier to find another board. I need more experience and this is fun.

F14 tomcat 029 (resized).JPG

f14 cb 007 (resized).JPG

Ya...I redid it pretty fast. It needs redone, to look a little better. Now, That I decided to just do it right. I'll either clean it up and do over, but I'll probably check out what your suggesting. That would be much better!

If you don't understand how it works? Just take it all apart! Yep, I was one of those kids they had to hide the tools from! If not? I was taking everything apart. My dad had an 8trck car stereo, I had to be about 6. By the time he got home from work it was in pieces. I still hear about it. 30 some years later.

I have a lot of time on my hands right now. So this will keep me occupied for a little while.

I started on it. I'm waiting on another fiberglass brush/pen. That is the only thing I could find laying around that works good that doesn't tear up everything. This part is going to take me awhile.

I started reflowing some of the traces, it's really tough to make it look good so I'll just go for solid over looks. I did manage to find some small wire to use to repair the fine traces. The cheap resistor assortments (1%) that are sold all over ebay with the super fine leads. Cutting those leads off works perfect for these small traces.

Thank You!!

This winter I plan on buying some real tools for this. I'm using a $10 soldering iron, old Radio shack flux that is a gooey mess to try to get off even with isopropyl alcohol, And my solder sucker is too strong, it's a cheap spring loaded thing that wants to suck the whole pad and through hole out if your not careful. I've gotten use to the Iron and the length of time to use it which is fast! If it doesn't go at first try ,let it cool, and go again or the pad and trace will burn off.

I think If/when I get a few real tools I might be a little dangerous!

Anyone ever try to adapt an old airbrush to make a small baking soda blaster for corrosion on boards? I wish I had a blast cabinet....So...I'm looking around the garage for a cheap(very cheap, like.... with things laying around ) way to build a small cabinet or even just use baking soda in an old stripped out airbrush. Mod it a little. Or even make a siphon feed type deal like what use to be used to spot blast cars, only smaller.

I know we used baking soda on small things, I wonder if it works on boards too?

I'll just keep adding here on the same subject.......This is an F-14 Tomcat project.

I did some parts trading and ended up with a parts board. The sad thing is? the parts board looks to be better than what I started with ...with the exception of two cut outs and a burnt spot on the back. Either way I'm happy to end up with it and think I'm going to try to repair it along side the other as I go. Just to see if I can fix it, and to have a spare test type board.

F 14 parts board 003 (resized).JPG

F 14 parts board 004 (resized).JPG

F 14 parts board 005 (resized).JPG

F 14 parts board 006 (resized).JPG

I didn't think of it that way. I was just thinking of trying to blast with something that wasn't so abrasive. Baking soda came to mind since we use to use it on small pieces. As a blasting medium. That was the thought last light night anyhow. I guess I'm just playing around until I get more materials.

I had big plans when I started this.......Now! I'm down to just getting the corrosion cleaned up and get it working. I think I'm making more of a mess and causing more damage by trying to re-tin. I just can't get it to look right with what I have to work with.

I'm still working at it!! It won't be pretty but it will work again! I still have a lot to do, I've been picking at it here and there. I'll work on pretty on the next one...maybe...!

A 001 (resized).JPG

That's my problem...I can't control the flow. I'm fast enough that I don't burn traces unless they were already too thin from corrosion or sanding too far, but it's hard to control the flow. I even made a small tip, that worked better...I just had to load and wipe off the tip often. I'm still playing around. I didn't give up just yet.

I was able to cover the traces. All I have for a solder sucker is just a cheap spring loaded thing with a nylon tip(or whatever the tip is).

So, It's not pretty, it's a lumpy job. I need a real soldering station and sucker.

I'm fixing the traces now. This whole thing is just a practice and to see if I can save it.

I'm getting there slowly, it's not going to be pretty but should be solid.

trace 006 (resized).JPG
trace 007 (resized).JPG

Here I'll give you a picture.....

Do you think I should refile my tip? I'm joking!! But I do have to refile it all the time. I don't know if it's just because of the cheap Iron or if I'm doing something wrong. But I chew the tips up pretty fast.

also a Pic of my "work area"...My bucket seat and tote table. Can't get much more "hack" than this.. I mean A pink lamp?

I'll make it work! It might take me a little while! I'll use a rock if I have to make it work for something. haha

work area 001 (resized).JPG
work area 002 (resized).JPG

This part is ugly, but I stitched it back together....This paste flux is a mess to use. Sticky hard to clean up. I still have some more cleaning to do I just rinsed this section real fast...

I also had to reuse a few old parts. If they don't work I'll change them out later...

Ugly but here it is... I checked most of the connections with the meter. So I think it might work....

S 005 (resized).JPG

After looking at the pic I see some spots that look bad(not connected). They are, even though the pic shows a gap or unconnected part. I think it's just the way the pic came out. It's hard to get one that isn't glared....I see a solder connection on the board but for some reason the pic makes it look a gap.

Ok it's back together and still doesn't work.

The first 6802 was bad. I swapped it and now have another issue that I'm stumped on.

Reading the Link in post 13, It says that pin 24 of U15 should be around 1v. I have 4.9v. I bent the leg out on the 6802 and the chip gives .6v, Ok so I know or think it isn't in the cpu. Looking at the schematic I'm completely lost! That should be A14(?).

Edited......Just trying to track down the bad chip. I'm not sure how it's 4.9v.. But I'm still trying to figure that out.
'

I'll do that....

I also have the reset grounded, or the circuit isn't working. Those are the two things I've found so far... After figuring out the first cpu I tried was bad.

I tried to keep a look out for splashes that were connecting. But I must have missed something. I had a lot of bad traces too that I patched or stitched, while looking at a parts board to compare. So, I could have gotten mixed up somewhere too and stitched something in the wrong spot. I tried to be careful and triple check, but it's a possibility.

Maybe I'm confusing myself. A14 is tied(?) to the 5v with R52(?). Across W4. That confuses me. I wish I knew more.

I just checked with the meter and I'm not jumped to the 5v. If I set it of the value of R52(4.7k), and jump to the 5v, it beeps. So, I'm guessing its good there and free. If that made any sense at all. I'm bad at descriptions...I'll try it again...

The resistance between A14 and the 5v is 4.67k which matches R52.Nothing lower than the 4.67k. So, I'm guessing there isn't anything shorting on the traces.

yes, 4.7k across the resister. It took 4.67k for me to get a beep. Nothing in the lower ranges.

Ok, w4 is installed. Yes, I keep looking at this logic stuff backwards. I worked on stuff for so long that was just simple on and off. And usually power added to make it work. I can't seem to get my mind to switch when I'm trying to learn this stuff. This is deeper than anything I ever had to do or learn. This is more fun though!

So, I need to go to U12 pin 14, U37 pin 5, U36 pin5.. And work it out from there? Or basically all the Ic's on the A14 line?

I know reset is held to ground. So , I don't know enough to know if that could be related for some reason. I'm hoping just a bad transistor. That sucks too! I have those all stitched in. So, I keep looking hoping not to have to pull them and check them.

Added..
What pulls that down to the 1v? The cpu? If so maybe I have another bad cpu! These were all used. I'll pull one out of my HS to check. They are Motorola in the HS, and I think I read somewhere that a jumper has to be changed...I'll have to go see if I can find that again...I may be mixed up.

Added again...
Never mind.. I swapped to a known good cpu and it's the same.

Think I figured out the reset or a possible reason why it's not working?... After reading a little and watching a short video...

If I have this right. ZR2 isn't putting out enough to trip the Transistor at Q37. I'm getting less than the 0.7v. If I understood all of that right. Which might make sense because ZR2 is only allowing(?) 1.5V.

No clue, I'm working at it though! I want to learn so I don't have to shotgun stuff. I'm still kind of unsure if I have the above right.

I know I'm making too many posts in one night.

I couldn't go to bed until I at least figured out the reset problem....

ummm?? Ya...You know those src's? And when the alternative is used the 10th pin needs to be cut off? Ya....I forgot!!

So.... I took the easy way out and just cut all of the ground traces to pins 10.

But now reset is working! I think....

IRQ 4.9v,VMA is 4.4v, and A14 4.9v. I've checked and rechecked the traces and sockets over and over I keep looking for a bad trace or short. Kind of stumped....... but looking at U36 now. My only reasoning is that It's common to A14 and IRQ.

VMA? I have no clue at all yet, not even an off the wall guess. yet!

Added...Nope, not U36 it's working! But I now know how to read that and what it does!

For you guys that know this stuff......Or system 11a

Can someone tell me if I have to have sound roms (U21,U22) or the CPU at U24, to get this too try to boot?
It didn't look like it. But I still don't know enough. It looked like it was it's own circuit for the most part, but I wasn't positive.

I have a mess and want to try to rule out what I can. After looking at this thing over and over...I'm convinced it's a bad Ic somewhere or maybe even a few. Or I keep overlooking a multiple shorts.

Thank you! I'm trying to find things to eliminate until I find(stumble into ) the problem.

What would cause CPU's not to pulse but have the correct V on most pins. I stuck them in my "parts board" gave it power and the lines are pulsing.

Added...
Nevermind.....I have one CPU that Pulses and one that doesn't. Might explain my problems....I thought it was good and it must be bad too! I'm chasing some problems that seem to change depending on which CPU I had in. Ugggghhhhhhhh!!!!! Hopefully, I have a good one now!!! I thought they were all good...But it's not looking that way.

That solved the A14 problem....This is the 3 CPU I've had in....

I might be mixed up since I've read so much stuff the last couple of days and my memory stinks...

I thought I read something somewhere that if a Motorola (6802) was used in a system 11a board something else had to be changed. Can someone tell me if I misunderstood or where that's at? I can't seem to find it again.

Added.... Finally found it again ....If anyone else would happen to run into this looking....

Taken from http://techniek.flipperwinkel.nl/wms11/index1.html

"If a Motorola microprocessor is used, W16, W17 must be connected. If any other brand of microprocessor was used W16, W17 must not be jumpered."

I'm guessing W16 if it's used in U15, And W17 if it's used in U24..

I looked and looked, and couldn't seem to find it. Then after I posted I ran into it again...That's happened a few times now.

Thank you! For confirming that. after looking at the board...I thought, I don't need to change both jumpers. If I'm using it in U15...But wasn't positive,Just a guess.

I think I have most of the board stable(meaning found all the iffy connections) ... Reset works at every power up now.

Right now Everything on the cpu checks out except the voltages for Pin 4 IRQ pulsing at 4.2v and pin5 VMA at 4.9v not pulsingt. It doesn't check out with the Link in the earlier post. That link says they are supposed to be around 2 to 3V.

Still at it! If I could just get a flash..Something... out of it I'd be happy for now!!

Thank you!

I'm Having a blast working on this but at times I'm ready to 12ga it!

SR2 is good. I swapped it with a new one. I checked it before I put it in the board. I was also able to pull one of the lines back down some (can't remember which one now) With a 4.7k resistor. Not sure if it was the right way, my way of checking for a short in that case.
IRQ quit pulsing...Maybe it had a weak connection and finally unconnected. haha

For anyone else reading...
And something I would have never thought about.
My PF is pretty much empty. I have a flourescent desk lamp sitting on it pointed in the back box.....If the wires for the logic probe get near the base of the lamp the logic probe will pulse when I get it near the board. If my elbow is touching the base, probe in hand, towards board it will pulse. No clue if the plastic base static is what causing it... Just really weird!! Now I have an extra ground wire running to the machine! I'm just taking a wild guess... I know I had at least one CPU set on that lamp base, may be why it's bad when I thought it was good originally. I also had all my transistors laying on it when building the board and who knows what else. I probably fried everything with static!

Just plugged U31 in the board backwards...... I can't believe I just did that. I smelled something getting hot! Looked up and noticed the notch was on the wrong side!

I need a video of this stuff! The bloopers reel!

I'm not even going to try it. I hope it didn't fry anything else.

I have to look this up..And I know someone told me this before. But I'll ask here in case someone knows before I find it. Can I use a 74HCT00 in the place of the 74LS00? I know someone told me you can interchange sometimes, but I can't remember which way.

Added... found it from what I understand the The HCT can be used in place of the LS, can't go the other way.
In case someone else wanders around looking for the answer..
https://electronicsclub.info/74series.htm

IRQ will start pulsing if I touch the top of the transistors in the reset section. That's with me grounded. So there is something flaky there. I don't have to put pressure on them, just touch the top. I found it by trying to flex the board a little, and started pushing around a little looking for a bad connection. So, I'm guessing it's in that section? Time to redo it with new transistors, just in case. Then I can rule it(that section) out for sure!

Maybe I got them too hot, I was on them pretty long when soldering, they were also on this static lamp base too.

VMA and IRQ started pulsing after I redid the reset section...Again.

Ok everything is now down to A9 not pulsing.

But I have a locked on diagnostic LED now. Not sure if that's moving forward but It's at least something different!!!

My V went up too for some reason. 5.4V now. Not sure why it went up. It was at 5v. until today.12 is a little high now too!

With the board unplugged and one probe at the base of the ground stud, and one at the base of the 5v. I get 29.71 ohms and dropping slowly. A couple minutes later it's in the 28.15 ohms and still slowly dropping. Checked again and it's at 26.7 ohms and seems like every time I check it's going lower. Out of curiosity what is that checking for?

5v jumps around depending on turning it on. It's either at 4.9v, 5v, or 5.4v. No idea if that means anything but something I noticed.

IRQ and VMA pulses when it wants too...I think I have VMA pulsing at every turn on now. But IRQ is still hit and miss at start up.So, far it seems like it works after the machine has been sitting off and when I come back later, turn it on to check things out, and it works, then after a while just goes out(stops pulsing). I'm stilll checking stuff on that.

A9 still isn't pulsing.

A9 works now....IRQ still not pulsing..

I have a parts board, plugged it in and put the CPU in it. A9 still didn't work. Took another CPU out of another game put it in this board and now A9 works....I must have had a bunch of bad CPU's. First thoughts were bad connections on the socket, but I've checked it multiple times. I checked that line, looked up IC's checked and checked...Wish I would have figured that one out earlier! I learned a ton though by looking things up.

Looks like I need to find a pile of spare GOOD CPU's.

Well? I started out trying to make this board nicer! Now? I'm just after "make it work". When I'm done butchering this thing I'll take a pic for the "worst hack" thread.

I've soldered and unsoldered too many times with my cheap iron. I did ok at first but after a few times these boards just won't hold up. I have learned how to repair traces, solder legs on chips, etc.... pretty fast now!! I understand A lot more than I did when I started this thread, and a lot of stuff came back from previous help on a Bally from Quench. and thedefog too! And everyone else that has given me direction.

You guys have taught me a lot!

Still working (butchering and shotgunning it) on it!! I'll get it eventually!! And when I give up? I have a parts board I can patch up for the game. But I don't really want to go that route. I want THIS one to work! This is art now!! A sculpture!!

I have a dumb question...I'm trying to learn this board and what's going on..

On a 74LS00(U31) if the inputs are pulsing(1 and 2) should output pin 3 also pulse? Or does that depend on the timing of the input pulse? If that makes any sense at all. 4,5 and 6. Are the same way, inputs pulsing output high, no pulse.

Just in general if the outputs aren't going anywhere.

Can someone explain this in simple dummy terms? Does it depend on input timing? The two input pulses aren't ever hitting a high at the same time?

Added...Never mind...I now see it at U36 pin 3 and 6, the pulses are alternating(?) to pins 1 and 3 of U31. I always ask these questions then stumble into the answer after posting.

Thank you for the link. I'll play around with that.

I've been jumping around this board just looking at what does what and if it's working like it should.

I still have a VMA, pulsing sometimes and sometimes stays high at 4.9v. I wasn't sure how it's supposed to act when there isn't a U27. Going to the Leon Borre site. I still have voltages that aren't matching at the CPU. Pin 18 is a little higher, and 24 and 25 are high and aren't around the 1v.

Every time I turn this on I get something a little different. Not much, but differences of .2 to .4v everywhere. It's not consistent. Reset line can be anywhere from 4.8 to 5. Even if I ground it for a second. It just depends on something in the board at turn on. Maybe none of that matters, I just can't find why. So, I'm wandering around looking for a bad IC.

I'm using the game power supply.

Most all of the IC's that I changed were 74LSxx, I did swap one for an 74HCTxx and two others to 74HCTLSxx. I was under the impression that some could go one way but not the other, I may have understood wrong since I'm just guessing at most things . I'll look at those again. I'm pretty sure the HCTLS are ok for LS. I'm not positive about the HCT in place of the LS though. I went to this link.. https://electronicsclub.info/74series.htm

I might be all mixed up on that stuff too!

Here's what I changed..and maybe it's part of my problem with the board...
U31 is changed to a 74HCT00N
U14 is changed to an 74HCTLS02N
U32 is changed to 74HCTLS08N

I can change them back, to see if there is any change, I'm almost sure the HCTLS are ok replacements. The other I'm not positive on.

Here is the link to the HCTLS

http://www.bitsavers.org/components/samsung/1990_Samsung_AHCT_HCTLS_Data_Book.pdf

I know you said the 74xx above, but I haven't changed any of those yet . Most of the IC's I've been playing with on the board so far have been LS.

I have something messed up for sure! I can't even get it into any diagnostic flashes yet.

I changed the caps on the power supply, It's been reading the same. It's my 5v and a few others on the board that seem to change a little depending on power up by, it may not be a big deal just something I noticed. Sometimes it's at 5v even, and others 4.8v.

I have my "parts" board going into diagnostic mode and flashing...The thing is missing 2 pia's U41, U54 and U42 is half unsoldered. A couple other Ic's at U17 and U45. Has a hole cut in the board with traces out at SRC8, half corroded Bad too, I can't even believe reset works, burnt,missing transistors and the sr's src's etc... And I can get it to try to boot and flash consistently. All address and data lines work. So, I know now that this 6802 is probably good along with another one that I thought was bad. They both work in this board. I even took corroded Ic sockets from the sound section and just half ass tacked them in for U27 and U26 (I didn't have anything else laying around and barely soldered them in)!!!! haha It was missing the 555 and I found one that I've been kicking around on the floor,straightened the pins, and stuck it in there. I don't care about this board right now and I could probably get it running quicker!

So, On the board I'm trying to fix I have to be overlooking the simplest thing. I'm missing something that is probably so ridiculous, I'll be too ashamed to tell anyone what it was when I find it!!! From the looks of it they should run the diagnostics pretty easily.

Still at it!!!