65XE boot issues

[guus.assmann]

Hello,

Good to read that I'm contributing.

If it's not solved with the MMU, then we'll keep rethinking.
I'm positive that it's possible to get the board 100% again, it's working for a big part anyway.

Pitty that UK and NL are so far apart and postage is not so cheap.
Anyway, keep up the good work.
If at first you don't succeed, try and try again.

BR/
Guus

[ziggy]

Hooray, a huge step towards success was made
The MMU from the 130XE makes the 65XE boot! Sort of....
The board jumps right into the Diagnostics program and starts the tests on its own. Both ROMs are checked and seem fine. The following RAM test immediately breaks the Test, only video garbage after that.

I conclude:
The MMU is faulty and trash. I will need a replacement.
The RAM is trash (?), but not all of it. After all, I was able to play Star Raiders II.

I have some spare 4164 RAMs on the way and will test which ones are faulty. I don't know how much RAM Star Raiders II needs, but my uneducated guess is that there can't be more than one or two broken RAMs.

Will update about my progress when I return in 3 weeks
Thanks to everyone helping me out! I appreciate it. With a "little" effort you can get any board running again

[guus.assmann]

Hello Ziggy,

Good to see that. Also good you didn't give up.
Now you can also consider to expand the memory to more than 128K.

The memory error must be a defect in the address lines.
So check the lines between the Freddy chip and the address-lines of the Ram.
Also, the address lines from CPU to Freddy can be at fault.
Fortunatelly, a Ram address line defect is most likely.
Check for lines being stuck to 0V or 5V. Interruptions between Ram chips can also be the case.
An Ohm meter with the computer switched off should be fine.
And in case of a short or missing connection somewhere, the "piggy back trick" will not work.

BR/
Guus

[ziggy]

The Memory upgrade does sound promising. The 65XE is not mine though, I'm repairing it for a friend and I think he wants to sell it.

Will do the address line testing when I'm back!

Greetings

[ziggy]

Hi,
I'm back and have got some updates.
My replacement 4164s arrived and so did @guus.assmann set of two MMU replacements.
Now, where were we? A reminder:
65XE didn't boot or go into diagnostics. weirdly enough, with "Star Raiders II" inserted it booted the game.
Now, I put in a known working MMU from another 130XE. Blue startup screen comes up with the usual noises. But the OS fails to load and goes into diagnostics.
ROM & RAM test passes the ROMs without problem, but immediately crashes / garbage or blank screen / on the RAM tests. No matter which RAMs I use (I have +30 available).
Keyboard test comes up fine. the function keys at the top (START, SELECT, HELP etc) work, but upon pushing one of the normal keys: Crash.
Tried a different set of ROMs (thank you Guus!), same behaviour, so the ROMs seem fine.
Strange enough, both (!) MMUs supplied by Guus fail to boot the system - red screen or nothing at all. How weird is that?

There seems to be so, so much wrong with this system...
MMU? I thought so... but the system fails to boot, with all FOUR different MMUs I have available.
Keyboard controller? The crashing keyboard test seems to point that way.
ROM? Is working.
RAM? Don't think so.

I'll gladly take any ideas

Cheers