Author Topic: X68000 (first one) repair  (Read 1013 times)

Offline aje_fr

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X68000 (first one) repair
« on: December 09, 2016, 08:28:04 am »
Hello,
 Well, I own two of this beauty and both have nearly the same defect.
 Obviously, I wanna repair them !
 I isolated the defective board, and problem comes from the motherboard.
 The motherboard did not start at all, only leds comes on.
 There is even no video sync on monitor.
 I tried to watch cpu signals, looks like roms is read for few seconds and cpu comes in idle.
 Is there common issue with this first generation motherboard ?
 I tried to swap cpu with a working one, same effect.
 Battery was dead but no traces were broken.
Thanks for any help
Bye

Offline neko68k

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Re: X68000 (first one) repair
« Reply #1 on: December 09, 2016, 12:58:26 pm »
If it hasn't been recapped, do that first then get back to us. If it has been, then I don't know ;)

Offline caius

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Re: X68000 (first one) repair
« Reply #2 on: December 11, 2016, 08:29:50 am »
Which model are?Did you already try to replace PSU?

Offline aje_fr

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Re: X68000 (first one) repair
« Reply #3 on: December 12, 2016, 08:15:54 pm »
Which model are?Did you already try to replace PSU?

The very first one, CZ-600C.
Obviously, I made my test with a known working psu.

But after few measurement, I may have found my problems.
On both motherboard, the 69Mhz oscillator is not running.

The main challenge now will be to find two new one...  :'(

Offline caius

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Re: X68000 (first one) repair
« Reply #4 on: December 16, 2016, 12:52:53 am »
You could generate the right clock frequency using a DDS :

https://en.wikipedia.org/wiki/Direct_digital_synthesizer

Offline JulBS0

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Re: X68000 (first one) repair
« Reply #5 on: January 28, 2017, 12:03:04 pm »
Hi everyone,

I had a similar case (original X68000 from 1987, with rust everywhere and a leaking battery), with (among other problems) a nonfunctional 69MHz oscillator.

I ordered a Cardinal Components' CPP series programmable oscillator, clocked at 69.552MHz, and after butchering my motherboard, my X68000 now starts and displays the "Please insert system disk" message  :D

The oscillator replacement process wasn't simple, because on these programmable oscillators, the pin 1 is not the ground, but a positive Output Enable signal. So you'll have to find a clean way to let the pin 1 float (an internal pull-up will enable that signal). If someone knows how to properly do it, please share your knowledge.

I ended up using a cutter, a soldering iron at 350°C and several hex keys to file the hole on the motherboard and prevent the pin 1 from touching it, this is a complete mess but it works.

There MUST BE a cleaner way lol.

EDIT: here is a link to the oscillator data sheet: http://www.cardinalxtal.com/uploads/files/cpp.pdf.
The "field oscillator programming instrument" is expensive, but Digikey (and probably others) can program them for you when you order the oscillator, without charge.
« Last Edit: January 28, 2017, 12:11:58 pm by JulBS0 »

Offline kamiboy

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Re: X68000 (first one) repair
« Reply #6 on: January 28, 2017, 06:52:53 pm »
Does anyone have a cap chart for the PSU of the OG X68000? The closes one I can find is one for the ACE, but I imagine they made changes to the PSU in that revision.
« Last Edit: January 28, 2017, 11:56:21 pm by kamiboy »

Offline JulBS0

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Re: X68000 (first one) repair
« Reply #7 on: January 28, 2017, 10:35:06 pm »
Here are the caps found in the original X68000 PSU (model number UADP-0047CEZZ):
  • C714 - 4700µF 10V x1
  • C721 - 2700µF 35V x1 (no more available? replaced by 3300µF 35V, seems to be working)
  • C715, C716 - 3300µF 10V x2
  • C718 - 2200µF 6.3V x1
  • C719 - 680µF 16V x1
  • C706 - 470µF 200V x1
  • C725 - 470µF 35V x1
  • C724 - 470µF 16V x1
  • C720 - 47µF 6.3V x1
  • C709, C726 - 22µF 25V x2
  • C710 - 4.7µF 50V x1
  • C717 - 2.2µF 50V Non-polarized/Bi-polarized x1
  • C728 - 47µF 10V Non-polarized/Bi-polarized x1
« Last Edit: January 28, 2017, 10:46:46 pm by JulBS0 »

Offline kamiboy

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Re: X68000 (first one) repair
« Reply #8 on: January 28, 2017, 11:57:09 pm »
Thanks a buncha muncha.