working on a Model 1 4K Level 1

[Dokken]

Will try today! for clarification, post 16 is referring to Z71 RAM shunt?

Z3 (ROM shunt) 01010110
Z71 (RAM shunt) 01111000. <--your suggestion?

currently Z71 (RAM shunt) is at 10101000 and works partially with video OK.

 

[daver2]

No...

I agree with the Z71 RAM links (my post #14) - these links define whether you have 4K or 16K DRAMs installed.

It is the Z3 links that I disagree with (see my posts #18 and 16 - in this order).

The manual page (post #12) identifies Z3 as associated with the ROM. This is NOT wholly correct. Half the links are associated with the ROM address decoding. The other half of the links are associated with the RAM address decoding.

It is the Z3 links associated with the RAM address decoding I am not fully in agreement with.

                   12345678
Z71 should be now: 01010110
Z71 should be:     01111110

Where 0 indicates OFF and 1 indicates ON.

Dave

 

[Dokken]

Yes!!

Z3=01111110
Z71=10101000

Your code box above says Z71 but you are discussing Z3.

thank you so much for your help again! I'll go hammer on this thing for a while and make sure it looks stable.

 

[daver2]

You are right, my post above should have stated Z3 not Z71!

Too many wrongs not making a right!

Hey, 15871 bytes free - exactly what I calculated. So the machine now 'sees' 16K of DRAM.

Ok, what's the next problem...

Dave

 

[Dokken]

Now I just need to find a RAM chip to get the thing upgraded to 4K from 16K! The site you linked to says they only ship in the UK.

it is highly likely I have one or more in some old parts boards, but for now I'll have to struggle with 4X the RAM.

Very odd journey, I know.

regarding next problem, none I know of yet! But I'm sure I'll find something.

 

[daver2]

The 4K DRAMs will be pretty obsolete.

But I am a bit confused by your statement above. Haven't you got it working with 16K and are you looking to return it to stock (4K)? I.e. downgrade, or is your statement tongue in cheek?

Dave

 

[Dokken]

tongue in cheek. I found this as a 4k L1 and my goal is to get it back to the original entry-level computer.

 

[daver2]

I thought it was...

I just thought, what you want is an MK4027 DRAM device. This is a 4Kx1 device (i.e. the 4K equivalent of the 4116).

The MK prefix signifies Mostek manufacture.

I had a load of these on my Nascom RAM-A board before I traded them in for the 16K upgrade!

These are in Dallas TX: 175694013716 on eBay, but there are loads of others... Check the datasheet for the speed (faster than 450 ns).

Dave

 

[Dokken]

it's fine at 16k for now. Since it is working, I'm happy to have a mint working level 1 machine which is probably very close to an original release. I need to check the serial to see how early it is. The case looks like it was never used.

at the same time, I have a non-working model 1 level 2 board on my bench which seems to have good power rails and CPU/clock activity, but no video output at all, not even a blip of anything. I was using this one for a reference on the level 1 machine. I may get put your remote diagnosis skills to work on this one very soon!

and as far as what's next after that model 1, in queue I have:

1- the external floppy drive for my PET that I need to get going (you helped with the PET a couple of years ago). I know the floppy has one blown tantalum, I need to find the cable, and I don't know the condition...it may work with minimal effort.

2- a CompuPro S100 I picked up recently. I tested the power supply, but no further. I have a feeling it will work based on the conversations with the guy I got it from. He took pride in it but was losing his sight.

3- a Heathkit H89 with external floppy unit. I did power test and boot it to a prompt, but that's all I've done with it.

So if you're up for the remote-diagnosis-repair challenge?

 

[daver2]

>>> So if you're up for the remote-diagnosis-repair challenge?

Always my friend!

You have some interesting machines there...

Dave