Nicolas Welte's RAM/ROM board problems...

Hoping that someone here has one of these boards and/or could help me trouble shoot mine. I've emailed Nicolas a few times now, but have had no response, so I guess it's time to turn to the awesome VCF gang.

I built this RAM/ROM board up over a year ago now (maybe even 2), but have only had a chance to try it out recently. Well, it doesn't work :-(
I have confirmed its lack of operation of the RAM/ROM board in my working PET board. I have run through Nicolas's troubleshooting guide at the bottom of the page here:
http://vic-20.de/x1541/hardware/petram-c.html

…Basically I can get the computer working with all IC's removed from the RAM/ROM board (except the 6502 of course) and the jumper wire from pin 10 to pin 16 of the GAL socket. The next step in the guide suggests putting in the GAL and trying again…this is where it fails with a screen full of seemingly random characters (although the characters are basically the same on subsequent restarts). So the issue is probably a funky GAL or my soldering. I checked all the solder joints and connections with a multimeter and they seem good.

I then borrowed a GAL programmer and downloaded the PETFLASH.JED file from Nicolas's page and reprogrammed the GAL16V8D. I've never programmed a GAL before, so I hope I have done it right. I tested that the device matches the buffer, and it did, so I think it's good. Putting the GAL back into the RAM ROM board and trying again produces a similar screen of garbage!!!!

I am not sure if any of the other components (Flash chip and 74HCT157) have problems as I can not progress to the next step in the troubleshooting guide until the GAL issue is fixed. One thing I am uncertain of, and the guide mentions nothing of it, is at what point should I remove the PET's onboard RAM and ROM.

HELP!

Thanks in advance

Phil

Nama said:

…Basically I can get the computer working with all IC's removed from the RAM/ROM board (except the 6502 of course) and the jumper wire from pin 10 to pin 16 of the GAL socket. The next step in the guide suggests putting in the GAL and trying again…this is where it fails with a screen full of seemingly random characters

Click to expand...

Assuming the GAL is programmed OK, I would think one of the five switches is not correct at the GAL input.

One thing I am uncertain of, and the guide mentions nothing of it, is at what point should I remove the PET's onboard RAM and ROM.

Click to expand...

Because of the LS245, the PET board can be totally isolated except for I/O operations, so the PET chips can be left in without bothering RAM/ROM operations.

Ah ha! Thanks dave_m, thats a possible breakthrough.

Seems the guy at the shop sold me a 10k (103) resistor pack instead of a 4.7k (472) pack, and I was stupid enough not to check before putting it in. This would possibly have a detrimental effect on the pull up resistor effect. Once the resistors was soldered in The DIP switches hid the numbering so it wasn't easy to spot the mistake without bending the pack to one side. Dave_m can you confirm that this is a problem before I race ahead and swap out the resistor pack for the correct ones. Thanks again for the clue.

Phil

Just to confirm, the code on the side of my resistor pack I have installed is 11X-1-103lf

Phil

Nama said:

Just to confirm, the code on the side of my resistor pack I have installed is 11X-1-103lf

Phil

Click to expand...

I wouldn't expect that to be a problem, but I guess it can't hurt to stick to the specs.

Have you confirmed that the contents of the flash RAM (or EPROM?) are correct?

Nama said:

Seems the guy at the shop sold me a 10k (103) resistor pack instead of a 4.7k (472) pack, Dave_m can you confirm that this is a problem before I race ahead and swap out the resistor pack for the correct ones. Thanks again for the clue.

Click to expand...

Phil,
From the schematic, it looks like the resistors are used as a pull down (to ground) rather than the normal pull up ( to Vcc) so the wrong value possibly could be a problem. Can you check the voltage at pins 1,2 and 3 at the GAL? If they are above 1V there may be a problem with using 10K resistors. The proper voltage should be less than 0.4 V for a good low level.

Hi again MikeS,
Hummm...I was certain I had found the problem, but you don't seem to think having 10k as opposed to 4.7k resistors makes much of a difference. I'll change it out anyway just to be sure.

I have not programmed the Flash ROM (or EPROM) yet as I haven't gotten to the part in Nicolas's trouble shooting guide where I install the ROM. I'm still trying to get the GAL part working. I can program A 27c256 or 27c512 anytime, so that should not be a problem.

Thanks
Phil

I received an email from Nicolas Welte. His diagnosis of my RAM/ROM board problem was spot on. Although I had a 10k resistor pack instead of a 4.7k, he thought that it shouldn't cause any problems, but instead he asked me to test the orientation of the pack. I was unaware that they were directional, and true to form, I had installed in backwards. A quick zip with the desolder station and reinserted it the correct way proved that he was indeed right. The board fired up perfectly the first time.

Great!

Phil

I've been trying to contact him to purchase a board for a while now. I've never heard back so I guess he has none.
(Still would love to get one of these for my 2001-8, that way I could run alot more and have access to basic 4.0 and disk drives)

Later,
dabone

Hi dabone,
I have been trying to contact Nicolas for months. He finally emailed today, and it sounds like he's been very busy with work and general life stuff.

I'd email him again as he's certainly around, just not very visible.

Phil

dabone said:

I've been trying to contact him to purchase a board for a while now. I've never heard back so I guess he has none.
(Still would love to get one of these for my 2001-8, that way I could run alot more and have access to basic 4.0 and disk drives)

Later,
dabone

Click to expand...

There are other options, although not as neat and flexible; what type of ROMs does your 2001-8 have, and is all the RAM OK?

My 2001-8 is now in perfect working order. It has 6450 roms and 6550 ram. First version of the shipping roms.

Later,
dabone

dabone said:

My 2001-8 is now in perfect working order. It has 6450 roms and 6550 ram. First version of the shipping roms.

Later,
dabone

Click to expand...

If all you want is IEEE disk access, you can replace the ROM set with BASIC 2 (3?) using one of Jim Brain's adapters, although it does involve running a few extra wires to the main board (no cutting though, so it's easily reversible). BASIC 4 would be a little more involved since there's no B ROM in the 2001.

I haven't tried it, but I'd think that you could expand RAM the same way.

There was another RAM/ROM plug-in replacement as well, an earlier version of Mike N's current RAM/ROM IIRC, which would be easier to build from scratch, but I don't know where the info is now.

you can replace the ROM set with BASIC 2 (3?) using one of Jim Brain's adapters

Click to expand...

You don't need one adapter per chip? And without something like this board, I don't think I'm going to get anymore ram.

Later,
dabone

dabone said:

You don't need one adapter per chip?

Click to expand...

Well, that's the easy way of course, but Jim's adapter decodes the addresses up to a '512 so you just have to connect it to the upper address lines and a small kludge to exclude the I/O area; a '256 gives you the option of selecting one of two BASIC versions.

And without something like this board, I don't think I'm going to get anymore ram.

Click to expand...

I've been meaning to see what's involved in doing the same thing with a '256 RAM chip in one of the ROM sockets, adding a R/W line and selecting the lower 32K instead of the upper half.

I found the other adapter I was thinking of, but unfortunately the supporting docs seem to be gone:

http://members.lycos.nl/ijmtu/hpbimg/pet2001rom_ram_Rep.jpg

Anybody recognize it?