• Please review our updated Terms and Rules here

working on a Model 1 4K Level 1

D

Dokken

Experienced Member
Joined
Feb 27, 2018
Messages
249
Location
TN
I've had this minty-fresh pristine machine in my closet for a few years. Had a garbage character screen when I found it.

I have it booting to a 'Ready' prompt after a Z80 replacement. I can type in a basic program and it will run. Mostly. it sometimes a acts flaky and will reset the screen when I hit return. Seems to reset after a period and loses whatever basic I had typed in.

I'm pretty sure one of the RAM chips is bad, as it is FIRE HOT.

I want to keep this machine as stock as possible at 4k/L1.

Questions:

1. the RAM is Motorola 3108003. I'm assuming the 8x of these is 4k? ?MEM just gives a WHAT? reply. Level 1 didn't have a ?MEM function?

2. What is a replacement part number/source for these DRAM chip?

3. what are the shunt setting options for Z3? can't find a reference on this. it works as-is, just curious.

Thank you
 
Z3 is named X3 in the Hardware Manuals (1978 & 1982) and Schematic. There are two Hardware manuals.
Pages 19, 20 & 21 in the 1978 Manual explains X3 and shows two shorting bars for 4K.

Tried to send PM! Enable PM's or send me Direct Message so I can forward URL


Larry
 
3 years later and I opened this machine up again. 4k level 1 with 8 Motorola 3108003. the last one gets smoking hot, I already had an X on it. the machine works for a few minutes then locks up.

What are replacements for this chip? I've got a box of old RAMs and some parts boards, but not having any luck. Manual says 4096 DRAM.
 
Thanks, Dave. I'll check it out and try to get some.

in the mean time, I put in 16k RAM and modified the shunt to the 16k settings. it boots to ready but P.M. returns 0. will a level 1 machine work with 16k?

I have other L2 16k machines, but am curious to get this L1 working.
 
Sorry, I accidentally included a [period] in the link!

www.silicon-ark.co.uk

MCM6604AC 4K dynamic RAM (sealed box of 4) - Motorola

MCM6604AC 4K dynamic RAM (SEALED BOX of 4 chips) by Motorola. Package: 16-pin CERDIP 3 state output, on chip address decode. supply : Vdd: +12V Vcc: +5V Vbb: -5V Idda : 50mA &nb
www.silicon-ark.co.uk www.silicon-ark.co.uk

I'll take a look at the schematics when I get back from my evening walk.

I would do a bit of research first though to ensure that the part(s) that are being sold really are compatible. See if you can find the data sheets and check the pinouts for your device and the one that is for sale.

Dave
 
I have found this manual that I am using:


It looks like the machine can be expanded from 4K to 16K by modifying the links X3 and X71 and replacing the DRAM chips with 4116 16K DRAMs.

The DRAM devices (4K and 16K) have to be faster than 450 ns.

The only thing that I am a bit confused is the schematic (and this is probably an error on the schematic). Pin 8 of the DRAMS does not appear to be wired. The Motorola MCM6604AC (which appears to be the Tandy part number 31008003) appears to be pin compatible with the schematic - except for pin 8 which is VDD (+12V).

You can measure the power rails on a device with a multimeter.

What actual DRAM devices are fitted to your machine, and what is the configuration of the two link blocks X3 and X71?

Incidentally, I suspect you can use 'standard' 4116 16K DRAM devices if you want to upgrade the machine - but let's not go there just now until you get the machine fully functioning and we know what we are doing!

Dave
 
thank you, this is a slow back-burner project for me. I have 16k RAM installed and I would get the ready prompt and could enter basic, but always got WHAT? in response. and P.M. always showed 0.

I started going through the CPU troubleshooting section. Capacitor C42 has something to do with the reset I believe and it was bad. replaced it and now I can enter and run BASIC. P.M. now shows 11775, so not sure what's up with that.
 
Hmm, that number is a 'magic number'...

If you had a 4K machine (that is 4096 total bytes) and we should get 3583 free, it means that 4096 - 3583 = 513 bytes are being used by the system software.

If you have a 16K machine, that should give su 16*1024 - 513 = 15871 bytes free. But it doesn't.

If you get 11775 bytes free now and we add the 513 that the system is using this gives us 12288 bytes in total.

Now, if I convert 12288 (decimal) into hexadecimal I get exactly 0x3000.

I am suspecting that there may be a bad link on one of the link blocks decoding the new memory.

It seems as though you have 12K of memory decoded as opposed to 16K.

Can you post a photograph of link blocks X3 and X71 please - and double check that the correct links are installed and the soldering is good.

X3 (in particular) should have a link between the following pins:

2 - 15
3 - 14
4 - 13
5 - 12

Dave
 
hmmm, I was using this set to level 1 (below). it show 2, 4, 6, 7 shunted for level 1. I'll try your settings. I have inserted dip switches in Z3 and Z71 for ease of changing. also, the reason I'm using 16k is that I'm missing a chip to make 4k.

I'll get back to you!
 

Attachments

  • TRS dip Screenshot 2023-10-23 at 3.33.49 PM.png
    TRS dip Screenshot 2023-10-23 at 3.33.49 PM.png
    439.1 KB · Views: 8
Hang on a minute - please do not TRY anything until we are clear what we are doing...

Let's get all of our ducks lined up first...

There are also differences with X71 based upon the revision of the PCB.

Can you post a photograph FIRST and I can double check the link blocks.

Also, can you tell me what revision letter of the PCB you have.

Dave
 
I don't agree with the Z3 links though.

Half the links (x4) are for ROM (as stated) and half the links (x4) are for the RAM (as is missing).

Dave
 
Ah, I think I have got it. I was reading the operation of Z21 (the ROM/RAM decoder) backwards...

I think you need to install the links ...

2 - 15
3 - 14
4 - 13
5 - 12

... for 16K (as I stated previously). All links for the RAM decoding must be installed in order to obtain the full complement of 16K RAM. Each link is 'worth' 4K RAM!

I am just wondering whether the Level I BASIC machine they are referring to in the table shipped with 4K RAM as standard and the Level II BASIC machine shipped with 16K RAM as standard?

They probably make no mention of a user upgrade from 4K to 16K RAM with a Level I BASIC. Who in their right mind would do such a thing :)!

Dave
 
1700069D is motherboard revision. the DIP settings in picture give the 11775 print memory and working basic system.

and holy key bounce, I'm sure this keyboard could use some care, but the bounce is bad. I remember having to load a de-bounce program on our old model 1 in the 80s and that was a level II model. I believe debounce was included in later level II roms.
 

Attachments

  • Screenshot 2023-10-23 at 5.42.12 PM.png
    Screenshot 2023-10-23 at 5.42.12 PM.png
    5.3 MB · Views: 6
  • Screenshot 2023-10-23 at 5.42.23 PM.png
    Screenshot 2023-10-23 at 5.42.23 PM.png
    5.3 MB · Views: 6
  • Screenshot 2023-10-23 at 5.42.34 PM.png
    Screenshot 2023-10-23 at 5.42.34 PM.png
    4.8 MB · Views: 6
It's great you have real switches rather than wire links.

I'ts getting a little late in the UK, but I would propose setting the Z3 links/switches as per my post #16 to see if we get the full complement of memory.

We can always reverse the action if we don't...

Dave
 
work day, so not much time. but I did swap the ram chips with 8 new 4116s I had (untested) and the P.M. shows the same 11775.

I fixed a dozen bad joints on the keyboard so it is now usable, so I typed in a ram test program from the technical manual. odd results. notice the WHAT? error and it has misinterpreted my line 10 slightly as P?OKE instead of POKE. it does this on various lines. what it lists is different from what it shows on the WHAT error.

second photo is a clean list. spacebar bounces hence the bad formatting.
 

Attachments

  • m1 Screenshot 2023-10-24 at 5.20.47 PM.png
    m1 Screenshot 2023-10-24 at 5.20.47 PM.png
    5.3 MB · Views: 7
  • Screenshot 2023-10-24 at 5.27.45 PM.png
    Screenshot 2023-10-24 at 5.27.45 PM.png
    5.5 MB · Views: 7
You must log in or register to reply here.
Back
Top