Ok, I'm not used to Zac machines yet, and I don't have the gear I used to for testing a non-booting board like this.

Basically, I'm suffering from a Devil Riders that won't boot. If I power it up, it constantly flashes zeros on the displays about every second. Reset line appears to be pulsing at about the same rate. Connecting CN11 pin 8 to 5v can get the reset line to a steady 0.6v, but doing a manual reset doesn't cure anything..... just shuts the displays off completely.

Doesn't respond to a Leon test ROM at all either. Either factory rom or Leon's gives me a steady LED on the MPU board. Doesn't currently have a battery installed, the good news however is there doesn't appear to be any battery corrosion either.

Somebody already went through most of the reset circuit, so looks like this problem has been going on for a while. Nothing I've poked at so far seems to individually be working wrong. But something is causing the reset circuit to keep firing.

I have checked Dave's page, as well as Leon's, but they don't cover a non-boot situation in any real depth. The reset circuit ties into a few different places, but I'm learning on it quick to try and figure this out. Not a complex board for the most part.... other than the reset and memory circuits.

I did disconnect the driver board completely from the MPU, so it shouldn't be affecting if the CPU is booting or not.

-Hans

Very cool, thank you. If you get that test rom, I'd love a copy.

I've been spending a lot of time digging over the schematic for the MPU board, and most of it makes sense to me now. Unfortuantely, those are also all the areas that aren't my problem. I am suspecting IC4 at the moment however. It does have a bit of a bubble on the top, so may have blown out when somebody was goofing around with the battery. I have some fresh 6514's on the way from Jameco, as well as replacements for IC14 and IC15, though I suspect the latter two are ok.

Eventually I'll tie all my notes together into something readable to put into pinwiki, as it's sitting almost empty.

-Hans

Don't worry, assuming I get the code updated for this, the only thing I'll be charging is return shipping.

I'll get back to this one Friday. Ordered myself a new oscilloscope, as there's a few things I'd like to document on this design for testing purposes.
A lot of things accessible to test, but only with the right tools. Voltmeter with half-assed logic probe feature aren't the right tools.

-Hans

Hmmm.... schematics don't cover that I can see. Where does pin 35 on the CPU chip go to?

My guess is it’s either pulled high or pulled low to lock it in a run condition. But I don’t have a data sheet for the 2650 with me right now.

J13/j14 is also undocumented. I’ll have to probably trace that the hard way when I get a chance.

Ahhhh, it’s an output. I’lol have to hook an LED up to it and see if does anything interesting. Probably not connected anywhere.

I used to have an old analog 'scope too, IIRC it was a 30mhz dual trace. Wasn't bad, but took up way too much bench space. Sold it a couple years ago when I stopped doing board repair for hire.

Just ordered a Sigilent SDS1102CML+

Also going to have to upgrade my PCB design software for the current project too, I just hit the pin limit doing my own version of the Gen2 CPU board.

A lot of time with the scope today trying to nail this down but just haven't had any luck.

Running the game rom, most of my test points appear to be doing what they should.

TP1 - Sense - Steady 5v
TP2 - Clock - 1.5mhz square wave
TP3 - Interrupt - 366hz square wave
TP4 - Reset ..... Not getting a high signal here. But jumping it high doesn't help either
TP5 - Interrupt - 366hz square wave
TP6 - Out counter - Square wave signal (Didn't catch the measurement)
TP7- Out Counter - Currently showing as low.
TP8 - Low ... whatever it is
TP9 - Clock oscilator - 6mhz sine wave.

My TP7 always matches my TP4. Not sure if that's supposed to do that or not. I need to keep digging into that.

Going back to Leons test rom now. I see good activity on the address and data lines. chip select looks to be running correct. Clock is fine. Reset line is pulsing.

As soon as I tie the reset line high, everything stops. Chip select stays high, no activity on the data or address lines. Only the clock lines show activity.

Yep, completely forgot about that. My head is still wrapped around how Williams works, and I was doing that wrong yesterday. I'm now correctly jumpering things to force the reset.

I think I may have at least found the symptom causing me issues, looks like a data bus problem. D2 is peaking at under 2v, all the other data lines are hitting 5v peaks. So something, somewhere, is screwing with that data line. Unfortunately, there are a lot of chips on the board that tie into the data bus. Never would have found that without a scope.

-Hans

All the data lines read the same. About 1Mohm to ground, and 30kohm to Vcc. Pullup resistors all still check at 10k.

-Hans

Actually, I think I may have found (that) issue. Started clipping/resoldering legs on anything tied to D2. It's either IC24 or IC25, because when I disconnected them from D2, everything seems to have woken up. I'm seeing a lot more address bus activity, and all my data lines are hitting a full 5v on their peaks.

I believe the LEON rom is now properly pulsing , but I need to make up a fresh test LED, as the on-board LED isn't working right. Though the inputs into that 3081 is shifting between high and low at the right timing. Looks like I need to get some of those 3081 replacement kits. Plus do something about those 40097 IC's.

Progress for sure. Going to see what else I can diagnose for today but going to hit a limit here soon without parts.

-Hans

Both are high on pin 6. I reconnected and disconnected that leg again a couple times, it's IC24 causing it. Makes an immediate difference to how D2 looks. Good to know about the alternate IC, I was kinda worried how I was going to deal with the dead 40097.

I suspect Leon's test rom was working the whole time though, but the dead 3081 was misleading me due to the LED being stuck. Now that I'm using a test LED like he describes, I can see the test rom is running. But IC24 problems would definitely cause the game rom to not run. If I'm understanding Leon's test properly, all my RAM is checking ok now too, which is good. Not sure if I'll do a remote battery or an NVRAM right now. I'll worry about that after I get the CPU board going. I'm pretty sure the driver is going to have issues going on too, so I have time to decide.

-Hans

Unfortunately, still stuck in the reset loop with the game ROM's. Did a verify on the ROM set, got an error, so I burned a fresh pair of roms. No change there either.

But already paying dividends for me picking up this machine. Ordering some 3081 boards of my own design tomorrow, bit different than the others on the market. Mainly wanted to keep it as close as possible to the original IC size.

I'm going to try MBT4401's, the SMT version of the 2N4401. More robust than the original circuits in the CA3081. Given how low some of the tolerances are, I'm surprised those chips don't fail more often.

-Hans

yes, the RFSH does have a very short blip going high. Goes high for 20ns every 4ms. I'll check the INTACK tomorrow

Yeah, hard to follow sometimes with all the things going different as I troubleshoot it. (also finding channel 2 is hard to read the text on the bottom of my scope. Have to see if I can change that). So I went back to remeasure what it looks like right now.

Currently reset line is pulsing high ever second for 100ms.
Reset matches TP7 identically.

RFSH is pulsing high every 1.6ms for 20us.

If I force the reset low, I get garbage on the displays. Once in a while it'll actually stay low on its own and gives me the same display garbage. Actually, this same display garbage also blinks into existence at the same rate/time the reset line goes high.... but don't know if it's before, during, or after the time that line is high.

-Hans

IMG_1601 (resized).jpeg

I'll check those more in-depth after work today, but at the moment I don't see any activity on the INTACK line. It's a solid low.

-Hans

Maybe. But isn't INTACK pulled high by R52, unless the CPU is forcing it low? Just not sure what the line is supposed to be doing. Would it be worth it to also watch TP5, to see if there's an interrupt request in the first place?

Might be a good idea to go back to Leon's ROM to check all the I/O's. I already know there are problems in IC24 and IC12 at the very least. So maybe something else is corrupting the data lines still that I haven't caught.

-Hans

IC24 was already a known problem, IC25 had a circuit as well that wasn't working right, so I removed both IC's.

No change to the boot issue though. I'll order more in a couple days...... need to get working on some orders for customers.

I have an older usb logic analyzer in the parts bin somewhere, but been a while since I’ve used it and would have to locate the software.

Plenty of parts on order at this point. Basically enough to rebuild the whole I/O section of the CPU board heading to C8/C10/C11 except the 3081's and pullups. Should be here by end of the week.

-Hans

Parts are here and I’m working on sockets for IC6,10,11,18,24,25

Not sure if this will help my no boot problem but I do know a couple of them are bad already. So I’ll get that done and reevaluate at that point.

I don't think they were all bad. But I do know IC24 and IC12 are were bad, and IC25 was suspect. I hate doing shotgun repairs, but I'm just completely lost trying to track down the source of my problem. So I'm taking educated guesses at what areas of the board might be causing the problem. That and a lot of this is a brain exercise to understand the systems on this board-set.

Going over the board, and looking at what's been noted on the schematics, it looks like I'm not the only one who's tried to find this problem. So I'm actually not 100% confident that I'll find it any time soon.

Well, sometimes a shotgun is the right tool for the job, she's booting, to a point.
Comes on, solid LED, displays stay solid, reset stays solid.

Plugged in the driver board, and I've even got attract mode running.
It's counting credits as I add them.

Still a few more IC's to replace on the MPU, including at least one 3081, and god knows what I'll find with the driver board..... but this is huge progress finally.

-Hans

IC18, IC24, IC25. But since I did all three at once I don't know which one did it.

I figured they were the most likely candidates as at least one was contaminating a data line that I knew of, and they were inputs into the data bus. IC6/IC10 were less likely but I did them anyway.

Still plenty of work to go, this machine is more of a project than was my understanding. But at least this is some big progress to get me going on other things. Will also 'start' a game at current too. Not playable by any stretch of the imagination but it's getting closer.