fadal 4020 wont boot

i get the scrambled screen on boot, if i use the J2 jumper it will boot in to diagnostics and i perfome the zero memory reset but upon startup after jumper removal i still get that screen, i tried it with and without the expansion memory module but nothing changes, if i try a cpu card from another machine it works. Is the cpu card totally dead? it boots on diagnostics but not in normal mode.

Is your backup battery dead?

It does no good to initialize the RAM then boot it back up with corrupted data.

If the battery backup is dead, the RAM will come up all garbled.

If it goes into diagnostics and the backup battery is above 3.0v, then perhaps the daughter card with the ROM program is loose or needs to be reseated.

You didn't mention what revision CPU card it is, is it -2 -3 -4?

if i try a cpu card from another machine it works.

Click to expand...

I think you've found the problem...

Is the cpu card totally dead?

Click to expand...

Dunno.. Its a FADAL!!! Power supply and voltages... Stuff gets old,
capacitors get a little cranky..

What power supply do you have in the machine?? What are your voltages???

That new power supply they've been selling for about 3 or 4 years, the one that
DOESN'T look like (and is) a PC power supply cures a lot of ills...

Here is a low voltage situation.. And it was SOOOOO Touchy.. If it fired up
at 11.86V, the machine would work.. 11.84, and the screen was blank. 11.85V and
I got garbage, and the garbage was always different.



One thing you could do.. Put your original CPU card back in, and then pull all
the cards that aren't attached to it... Leave the main 3 that are bridged.
You don't have to pull the OUT, just pull them out an inch so that they aren't
connected.

*********PUSH IN THE E-STOP..*****************

fire it up and see what happens.. That will eliminate all
the tiny voltage drains of the other cards, and let you know if your "bad" card is
still functional.. If your "bad" card itself isn't the culprit.

Check your voltages while you are doing this.

Remove your extended memory and try booting.

Perry Harrington said:

Is your backup battery dead?

It does no good to initialize the RAM then boot it back up with corrupted data.

If the battery backup is dead, the RAM will come up all garbled.

If it goes into diagnostics and the backup battery is above 3.0v, then perhaps the daughter card with the ROM program is loose or needs to be reseated.

You didn't mention what revision CPU card it is, is it -2 -3 -4?

Click to expand...

battery is good, im getting 3.6v the card is a -4 is there a chart for compatible cards?

It is a voltage issue, i tuned the pot down to 11.86 and it worked, but i'm getting a z axis fault, then i powered down and i get scrambled again, i guess i have to find the sweet spot or replace the power supply, it's one of the old stile with the big transformer on it.

thanks everyone for your help, i'll try to get another power supply.

I think he mean that 11.86 is the low voltage cut out, so as long as you are above 11.86v it's good. That doesn't mean the power is clean though, a noisy DC bus can cause all sorts of havoc. This is what Bob alludes to in other posts on power supplies -- just because a PS puts out the right voltage doesn't meant it puts out good power.

Perry Harrington said:

I think he mean that 11.86 is the low voltage cut out, so as long as you are above 11.86v it's good. That doesn't mean the power is clean though, a noisy DC bus can cause all sorts of havoc. This is what Bob alludes to in other posts on power supplies -- just because a PS puts out the right voltage doesn't meant it puts out good power.

Click to expand...

I highly suggest the new power supply they are selling.. It cures a lot of ills with boards that are getting a little long in the tooth.

i tried the card on another machine but it scrambles anyway, this card doesn't work on any of the 3 machines even without the ram expansion so maybe the card is just faulty.

The card is either probably aged out or needs some components reseated.

The -4 card is a PLCC 80286 processor last I checked. If you have a humid or corrosive environment, the pin connections can become oxidized.

I'm not saying this is the cause, but with old 80's hardware it wasn't uncommon to fix intermittent problems by reseating the chips. That means either just pressing on all the socketed chips to make sure they are seated, or removing them and putting them back in the socket.

You could also have aged out components like capacitors. IIRC, there is 1 or more electrolytic caps on those boards. Also, tantalum capacitors go bad over time too, especially in stuff that's from the late 80's and early 90's by this time.

Tantalum caps fail as a short circuit, pulling down the bus voltage, and if the power supply has enough oomph, exploding.

Some power supplies either have short detection or don't have enough sack to make the cap self-liberate.