maksg wrote on 2023-09-10, 17:56:maxtherabbit wrote on 2023-08-31, 16:05:I'm definitely right. I have a board with that exact same chipset. Find some 1MB modules with 9 physical ICs on them, trust me.
Thanks for the advice! It helped. Problem solved. It works just perfectly with 9 chips SIMMs. 4 Mb now on the board.
Great, glad you were able to finally acquire some.
Some report. The SBC actually stopped working. But not completely. It makes beeps and I see almost normal activity on the bus. In turbo mode complete silence. In non-turbo, it makes a long beep(not sure how many, one or more) and then eight(8) short beeps and one super short on the end. In turbo mode (12Mhz) I see activity on the board, but with no signs of life. I checked pin 23 on 82C104 (-PARERROR) and there are lots of errors, and seems that it completely unable properly read any data from the data bus when the turbo is on. And no errors on the data bus when NOT in turbo, but it gives beep errors described above, which means that it's unable to find the BIOS of the video card which is weird because the card is fine and ISA bus as well. So I supposed that this was maybe RAS and CAS, and did tons of reverse engineering work and checked all logic responsible for CAS, RAS, TURBO, and MEMWTST, with no success. However, I noticed that the signals from 82C101(system controller), pins 30(RAS), and 66(ENDRAS) look not correct. They look not as they should be, because for my luck I made a couple of screenshots from my oscilloscope at the very beginning of my learning of that SBC. And I assume that something wrong with 82C101. But not sure yet and keep tracing. I still think that the problem is not in the VLSI chipset. Can you guys suggest something? This is a very odd issue and a good troubleshooting challenge.
p.s. I also checked U6 (PAL16R6BCN) and that PAL works 100% properly. It was the most suspected circuitry on the board.
p.p.s. And I'm sharing scans of my reverse engineering work, maybe it will help someone.
Good work, I saved the diagrams for furture use / reference!
I still have one mainboard with a defective 16R6 PAL - so they do fail sometimes indeed.
I haven´t come across a defective VLSI chip _yet_, in most cases of "weird behaviour" there were bad soldering joints at one of the chips. Today I reflow all the VLSI chips before starting any further troubleshooting. In most cases you cannot see the interruption and they don´t react on pressing down the chips.
majestyk wrote on 2023-10-11, 16:12:Good work, I saved the diagrams for future use / reference!
Thanks. Here are a couple more diagrams and pictures. I also added reverse engineering for another 286 motherboard which I called MB2. The schematic looks a bit different but the conception is completely the same.
I’m already close to starting to transfer all this to KiCAD, I’ll see what happens with my free time. I have added a significantly updated and refined wait-state and turbo circuit scematic. I also noticed that the PAL16R6 uses only 3 output pins - ROMWTST, XTAL 2(2) and SYSCLK, and nothing more. All other pins 13-17 are not used anywhere. And despite the fact that pins 3-8 are connected to A0, A1, -S0, -S1, etc., they are not used anywhere as well on that chip. I still don’t understand why they had to be led to this PAL.
Further. I resoldered all VLSI chipset connectors and it didn't help. SBC still not working. But I found one strange thing. The screenshot is attached. I compared -S0, -S1, A0, and A1 with the working 286 motherboard (MB2) with this SBC and noticed that the signal looks almost normal, but something is missing. It seems that some chip is not receiving some signal. But I can’t figure out which one it is. I can’t understand how exactly the -S1 signal is generated. Accordingly, with datasheets, it's generated by the CPU. It is out of the CPU and going to 82C101, after which it receives full formation and here at this stage, something does not work as it should.
I can confidently say that I have carried out a complete reverse engineering of the main parts of the board and if desired, all this can be transferred to some kind of CAD and we will have another open-source project, but for 80286 based on VLSI.
I elaborated some of the PAL connections here:
Thank you for the URL. I found a lot of useful information there. I haven't come close to analyzing this PAL yet, but getting close. I will double- check the pinout for the PAL on the SBC. Seems we have some differences with yours.
It fixed! It's freaking working! I can't believe it. It was 82c101, as I thought at the very beginning. Actually, my research of all signals and tons of reverse engineering work brought me to that circuit. VLSI's datasheets helped a lot. A broken S1 signal with a fully functional CPU, leads to the obvious conclusion that something is wrong with the system controller. But I wasn't sure till replaced it. Thank you majestyk, your advices were helpful.
p.s. And first time, I soldered a PLCC socket onto a board. For the first time, I would say, not bad at all.
Congratulations 😀 Great news that it wasn't one of the PALs after all and your troubleshooting / reverse engineering was quite educational.
How did you solder down the PLCC socket? Usually I'd end up melting some of the plastic on it fitting them.
Thanks!
I used MHP30 and hot air 957DW+. This is not super professional equipment, but enough for my hobby needs. MHP30 has a pretty annoying interface, but it works, though.
>Usually I'd end up melting some of the plastic on it fitting them.
I damaged the socket with hot air on the first try. This is essentially a second socket. (I counted both attempts as the first time). On the second socket, I lowered the temperature a bit and tried not to get the hot air too close to the socket, but enough to melt the solder. On MH30 I set around 250C and the same for the hot air.
Hey, that´s good news - congratulations!
Where did you source the replacement chip?
I must admit I still solder these sockets with my regular soldering iron with a small pointy tip.
rasz_pl wrote on 2023-09-06, 17:07:https://www.vogons.org/thumbs/47112_18b3724ff52d48d54756df0baef7d798/interrupted_track.jpg […]
maksg wrote on 2023-09-03, 20:05:Also noticed quite a weird thing on the SBC...
majestyk wrote on 2023-09-04, 06:45:Traces with an "open end" are often grounded and have some shielding function to prevent signals from interfering with each other.
Otherwise I could think of a sloppy rearrangement between different revisions of this SBS, but that wouldn´t be Taiwan-like...
Yet ATA66 IDE cables use 80 conductor wires with every other wire a ground following the ultimate in guard wires and impedance
I have four 286 boards with VLSI chipsets. I had to sacrifice one of the most unstable and buggy ones.
>I must admit I still solder these sockets with my regular soldering iron with a small pointy tip.
This is actually quite cool. This approach requires strong focus. How did you unsolder the chip?
rmay635703 wrote on 2023-10-22, 17:17:Yet ATA66 IDE cables use 80 conductor wires with every other wire a ground following the ultimate in guard wires and impedance
The same applies to cables for FDD.
The VLSI 10x series chipset is one of the most common. Thankfully relatively easy to get parts
The SBC is fixed and seems to be working, but conflicts with some video cards.
I have:
1) STB SYSTEMS S3 P86C801 POWERGRAPH X-24 1 MEG 16-BIT ISA VGA CARD MXB81
2) Almost standard for 90th -Trident TVGA9000 ISA
3) Cirrus Logic GD54C1 ISA
And the SBC is actually conflicting with the first two and works stable only with Cirrus Logic. The conflict does not begin immediately. At first, everything works fine. But as soon as I launch some game that actively uses graphics, garbage starts appearing on the screen, and then everything freezes and stops working. Seems that the SBC still doesn't work 100% properly.
I found a problem - PAL16R6 is glitching. That is weird that it worked properly with Cirrus Logic. So, I inserted the working one from another 286 MB, and now everything works well. I even assume that bad PAL caused damage to the system controller 82C101. So, yeah. This SBC is completely fixed now.
The VLSI 16R6 PALs seem to be standardized for most VLSI 286 mainboard models. They are also getting quite hot during operation and might have a limited lifespan or just age and become instable.
"raz_pl" provided some links to a cloning project based on an Arduino board and I wonder if it might be worth trying that in order to make new PALs / GALs for the VLSI boards (and others):
rasz_pl wrote on 2023-04-18, 16:39:that R in 16R6 is for registers, afair those are unclonable if programmer used this functionality because logic can fold on itse […]
that R in 16R6 is for registers, afair those are unclonable if programmer used this functionality because logic can fold on itself (feedback)?
on the other hand this dude has a sketch ready for it http://www.vintagecomputer.net/fjkraan/digaud … ad/palread.html but Im dubious about its efficacy
Those guys are serious business cracking old arcades https://github.com/DuPAL-PAL-DUmper/DuPAL_Analyzer https://github.com/DuPAL-PAL-DUmper/DuPAL_Board https://github.com/DuPAL-PAL-DUmper/DuPAL_Ana … ocs/analysis.mdmight be easier to reverse engineer the board itself and identify what was this chip function to begin with
