GRiDcase 1520 with RAM error, GRiDcase 1530 with RAM error

[nolan7]

I have several GRiD computers—most of them work, but some are dead. I’ll discuss two of them here, as they have a similar problem.

The first is a GRiDCase 1520 LCD with eight 256K RAM SIPPs. It’s in excellent physical condition, but it doesn’t boot. It beeps 1-3-3, which, according to the service documentation, means:
"1st 64K RAM chip or data line failure - multiple bit." I tested all the SIPP modules in my RAM tester, and they passed every test, even under marginal conditions (voltage/timing variations). I also tried using different, known-good SIPPs, but the computer still behaves the same way. On the mainboard, next to the FPU and CPU, there’s a 40-pin IC marked "RAMC286". I swapped it with one from another working GRiD I own. It wasn’t the exact same chip, but the result was unchanged. I’m unsure if that was due to the difference in chips or if the real issue lies elsewhere on the board. According to GRiD’s documentation, at least two versions of this chip exist—one supports only 256K modules, while the other supports both 256K and 1MB modules. I took a bit of a risk installing a different one, but it didn’t damage the chip—after putting it back in the working computer, it still functions fine. So, the real issue in this 1520 likely lies elsewhere on the motherboard. This has been an unresolved problem for nearly two years now.

The second machine – GRiDCase 1530
Strangely, I recently acquired another GRiD with a similar issue. I bought a GRiDCase 1530 on eBay—an incomplete, dirty unit—because I noticed it had a 15-pin VGA connector instead of the usual 9-pin CGA. I wanted it just for its VGA card and LCD, but once I had it in my hands, I realized it wasn’t a lost cause. It’s missing some components—specifically, the entire rear top magnesium cover, the HDD/floppy module, and the PSU module—but otherwise, it’s intact. I thought I might be able to get it running using parts from other non-working GRiDs. A VGA-equipped 1530 would be great to have. However, it has the exact same problem as the 1520—it beeps 1-3-3 at boot. Once again, all SIPPs test good, and swapping in known-good modules made no difference. I know I can still use the VGA card and LCD in another GRiD originally built for CGA (as was my original plan), but now I really want to get this 1530 motherboard running!

I’ve collected maybe six or seven GRiDCase 1520s and 1530s over the years, and two of them arrived dead with the same 1-3-3 beep issue. Both were listed as "untested", of course. Has anyone seen this issue with these boards before? Any help would be much appreciated!

 

[Paralel]

The issue on the 1520 is likely board damage from capacitor goo. Thorough washing, replacing any caps, and then inspecting the connection between the RAM and the controller will likely lead to the discovery of either a damaged RAM socket or damaged trace(s) which you will need to repair.

Changes are the 1530 is suffering from a similar problem, it's also possible that the 1530 is suffering from some battery damage since the Tadiran on that board are like little bombs, unless it was recently installed as a replacement by you. Tadiran batteries hasn't changed their design for more than 30 years, so telling if one is now or old is difficult.

So, for both boards, I'd really start with a complete and thorough cleaning and recapping, and then go from there.

 

[0xDEADBEEF]

Not sure if it is relevant but my 1520 uses parity memory.
Otherwise, I would check ram address and data lines for continuity? Maybe the sockets do not make good connection?

 

[0xDEADBEEF]

I just played with 1530 and it beeped 1-3-3 when I installed SIPs in one set of 4 sockets (starting from cpu side), it started working when I used the other set of sockets. 1-3-3 is supposed to be bad first 64KB.
1530 uses 32 bit memory so one needs to populate 4 or 8 sockets, 1520 is 16 bit, so pairs of sockets need to be populated, not sure in what order though.
You can check pin 3 (D0) for continuity between sockets, if it is connected they are in different banks, if not connected then they are in the same bank.
For your problem I suggest maybe install minimum amount of memory and check continuity between the pin and socket on the motherboard. Also try cleaning the legs of SIPs with steel brush and contact cleaner and spray some contact cleaner into the socket?

From what I understand 1520 and 1530 both use faraday 3400 chipset, I saw some mention that here are different versions for 256K and 1M SIPs but all i have seen so far were 1M.

BTW, the 1530 that I just bought has RAM without parity so I guess no parity is fine.

 

[nolan7]

Mine is fully populated with 8 SIPPs. I have seen many of them and it is common to be just 8bit modules without parity, but thanks for pointing that out. I tested them in RAM tester and they passed every test perfectly. I tried another set of SIPPs from other working machine and it didn't help. I checked continuity of all 30 pins (according to SIPP RAM pinout) and the traces where they go. All data lines are OK, GND and +5V is OK, all address lines goes to some TTL logic or directly to the chipset. Friend of mine tested those TTL chips for me with logic analyzer and he says they are OK. I just don't have a way to test the chipset, but I am now suspecting either the chipset (data buffer is in one of the chips and address buffer is in another one, FE3020), or, that strange RAMCTRL chip near CPU, that one probably generates RAS and CAS signals, I don't know if those are correct. I have one other working GRiD which I could use for testing, but I want to avoid unsoldering this RAMCTRL, the PCB is quite thick and there are big copper layers inside, it is difficult to suck the tin out of every hole without damaging the PCB. I already removed some chips from this dead GRiD successfuly but I want to avoid soldering on working GRiD.

 

[0xDEADBEEF]

What i am thinking is the ram module legs does not contact the socket when it is inserted for some reason.
insert them one by one stating from the back and test the continuity between every leg and the metal ring of each socket pin. i know, 30*8 ;-)

 

[nolan7]

I don't think this is the case, but because of lack of better or other options, I will probably try that. It's not that horrible, it is quite doable. I will try that.

 

[nolan7]

I checked them all, from the pin on the SIPP module to the mainboard socket, they all make good contact. All 30pins on all 8 modules. My suspects are:
1. chipset (address buffer, data buffer)
2. RAMC286 - custom chip from GRiD, probably generates RAC/CAS etc.
3. logic gates through which address lines from RAM to chipset are routed

 

[0xDEADBEEF]

Damn I hoped it was someting like lack of contact with the pin in the socket.
I thought RAMC was rebadged Faraday 3xxx series chip? I think there are 4 Faraday chips on both 1520 and 1530?
Can you probe RAM signals with oscilloscope at boot to see if there is expected activity on different lines?

 

[0xDEADBEEF]

So, today I learned something about my 1530. I have installed 8MB RAM but it only saw 4MB, it didnt detect memory in 2nd bank.
Then I skimmed through the manuals and at the end of the disassembly section of 1500 hardware service course there are tables with ram configurations.
and it says that 4MB is with J3 installed and 8MB with J3 removed.
But I couldn't find J3 on my board, found some other hardwired jumpers but no J3. But there was J5 kind of close to memory and it was installed. So I removed it, and guess what, it detected full 8mb.
So I am wondering if jumper configuration may be an issue? Look for J3 and J5 (I think yours is in bottom right corner of your 1530). Try installing or removing them and see if it makes any difference?

 

[0xDEADBEEF]

Hmm actually it looks like J3 is right there under the ram sockets on your board, I have another board like yours, but mine doesn't not boot or beep at all.
I can see the clocks though and some activity on ram and eprom pins, so it is doing something?

 

[0xDEADBEEF]

well, here is fun thing. i am trying to get 1530 working and it mostly works, except it hangs when idle.
i tried different ram and cpu and it doesnt help. replaced cga, replaced battery backplane.
if i leave it for few minutes in dos prompt or volkov commander interface it just sometimes reboots or hangs, somemtimes volkov shows some screen corruption.
also funny thing, probably unrelated, when i use cx486drx2 and install thermal pad on it (i wanted to interface it thermally with keyboard backplate) it causes the machine not boot from hdd anymore. it boots from floppy but has the worst time accessing hdd.