65XE boot issues

[PhilC]

@ziggy reason for asking about the keyboard was vecayse you weren't able to boot into the self test menu.

[ziggy]

@PhilC
Hey, good point! "Start" definitely works in Star Raiders II, not sure about the others. Diagnostic should start by holding down "Options" while turning on the power, right? I could try shorting the two corresponding pins on the Keyboard connector. Just need to find out which ones...

[guus.assmann]

Hello,
Yes, in order to start a cartridge, the OS needs to work.
And the cartridge uses OS routines for the screen and keyboard.
The Basic Rom is the 24 pin chip.
Pin 18 is the CS to that Rom. If you interrupt that line or that pin, basic will not start.
In that case, the computer should end up in the self-test and that´s also in the OS-chip. That´s the 28 pin chip.
To get the selftest started, the option key has to work. Mostly also used in some part of a game selection in cartridges.
That option key is read by Pokey. The OS then sets a pin on the 6520 Pia.
This pin is connected to the MMU and that selects the part of the memory where the selftest resides.
You could also force just that pin to envoke the selftest. (If memory serves right) It´s a good idea to socket the MMU anyway and the you can leave that one pin out of the socket and connect it right.

Still, it can be a pain to troubleshoot this kind of fault.
I´ve added the Jedec file and the design file for a Gal16V8 based MMU. It´s a 1 to 1 replacement.
And the design file gives some description of the pins.

BR-
Guus

[ziggy]

@guus.assmann
Thank you for the tip with shorting the pins But I'm not sure which one I should short, it's a little unclear to me because you mentioned 4 ICs Pin 18 of the Basic Rom to GND?
Thank you

[ziggy]

I disconnected Pin 18 on U4, no change. Or do I need to connect it to something else?

[ziggy]

Can confirm Keyboard working, plugged it into an 130 and managed to access the Diagnostics. No further progress so far.
I don't get it.
The system seems to work.
Star Raiders II needs every aspect of the system (?).
So how can the system by itself not work?

[guus.assmann]

Hello,

Please also see the schematics.
And the Gal-design file has some comment with the controll pins.

For basic, I did mean an alternative for removing the chip, by just interrupting the signal to pin 18.

It's possible to "fool" the MMU by activating the pin that enables the self-test.

If the cartridge works, most of the system is ok.
Still, MMU or Pia can be defective. (partially of course).

BR/
Guus

[rubber_jonnie]

Can confirm Keyboard working, plugged it into an 130 and managed to access the Diagnostics. No further progress so far.
I don't get it.
The system seems to work.
Star Raiders II needs every aspect of the system (?).
So how can the system by itself not work?

Good to hear the KBD is verified

I think (And I'm sure somebody will correct me if I'm wrong) that when using a cartridge, it maps into the Basic ROM space, and so basic isn't used, rather the cartridge ROM is.

If I'm right, then you may have a problem with the Basic ROM not playing nicely, maybe stuck bits, ROM corrupted or something. If as @guus.assmann says, you can disable the basic ROM without removing it, that may help you get to the self test mode without pulling the Basic ROM.

What diagnostic tools do you have? Multi-meter, Logic probe or Oscilloscope? Whilst a scope is ideal, a logic probe has helped me a great deal, and they are quite inexpensive these days.

I'd suggest that you get a working 130XE next to it and if you can get a logic probe and probe each of the BASIC ROM pins on the working machine and compare to the broken machine. Unfortunately a multi-meter, whilst fine for many things, isn't good enough to check logic levels on the chip. Get yourself a pinout of the Basic ROM, print it out and then on the good machine, write down what you see at each pin, then do the same for the broken machine and compare.

[ziggy]

@guus.assmann
Hi Guus, thank you again for your time. I'm looking at the schematics right now.
I'm really sorry, I don't know if my reading comprehension is just screwed after days of looking at PCBs or you are not stating some things that might seem totally "obvious" to you, while they are not to me

WHICH Pin 18? Of the BASIC ROM? What do you mean by "interrupt"? Disconnect? Connect to GND? Connect to the MMU?
WHICH Pin triggers the self test on the MMU? What do you mean by "fooling" the MMU? What kind of "triggering"?

The labeling in the schematics is probably very easy for you, but for me? I just can't find any abbreviation on any of the pins stating something like "Self Test", "Diag" or something similar. Sorry

Thank you again

@rubber_jonnie
Mapping into the BASIC ROM would indicate a faulty BASIC ROM, which is ignored by the system when a cartridge is inserted. Is that correct?

Right now I have a Multi-Meter and a logic probe. Osci is currently not accessible. My IT-Club is closed right now, Corona and all.

Greetings

[rubber_jonnie]

@rubber_jonnie
Mapping into the BASIC ROM would indicate a faulty BASIC ROM, which is ignored by the system when a cartridge is inserted. Is that correct?

Right now I have a Multi-Meter and a logic probe. Osci is currently not accessible. My IT-Club is closed right now, Corona and all.

Greetings

Yes, that's what I'm thinking, once basic is mapped out, the machine runs. Can you check the pins on the Basic rom with the logic probe and compare to a working machine?