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Author Topic: HW problems/repair (Read 3327 times)

Offline Zozosoft

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Re: HW problems/repair
« Reply #15 on: 2013.December.03. 22:54:38 »
Quote from: jltursan
Sadly, the EP64 keeps failing, no black screens tho, only endless booting screen after pressing keys.
I suppose that there's some fault in the +9V voltage line of the bus. The controller seems to receive no power at all.
Have you checked the edge connector connections?
The motherboard (when the two screws removed) can move few millimeters in the case, and in wrong position the connection pins don't connect.

I remember from the old times, in Hungary few 100 machines were sold with the motherboard in wrong position so EXDOS didn't work with these machines. The Enterprise Service Centre corrected this problem for free.

If you removed the motherboard to assembly the expansion then possibly it is not in the right position. The best to do: attach the system bus bridge when the machine top is removed then you see the connection pins. Then fix the motherboard at the right position.
« Last Edit: 2013.December.04. 11:59:00 by szipucsu »

Offline jltursan

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Re: HW problems/repair
« Reply #16 on: 2013.December.07. 17:40:51 »
At last!. Afters some hours of tedious work and having replaced all the EP64 capacitors things didn't get better :evil:. As the alignment of the edge connector was correct I focused my efforts on the EPROM.
It turned out that I wasn't been able to make a 28C256 work (the EP64 always reports strange RAM amounts and "non working bytes", weird!); but using a TMS27C256-15 I was able to make the EXDOS controller work in the EP64!
Also I replaced the ROM burnt, I've finally used EXDOS13ISDOS10UK-ESP.ROM (big RAMdisk patched); so being different as my last EXDOS 1.3 ROM, I can't assure if it was the EXDOS ROM or the EPROM itself which was incompatible. Maybe EXDOS?

Some pictures:

http://imageshack.com/a/img23/544/63k9.jpg
http://imageshack.com/a/img34/8940/5odt.jpg
http://imageshack.com/a/img15/8417/hbda.jpg

Now, as a bonus, I've IS-DOS in ROM :)
« Last Edit: 2013.December.07. 17:48:46 by jltursan »

Offline Zozosoft

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Re: HW problems/repair
« Reply #17 on: 2013.December.07. 17:57:44 »
Quote from: jltursan
using a TMS27C256-15 I was able to make the EXDOS controller work in the EP64!
Great!

Quote
I can't assure if it was the EXDOS ROM or the EPROM itself which was incompatible. Maybe EXDOS?
I think it is the EPROM. All EXDOS version used both with EP64 and 128 on a lot of machines and no problem.
(Only one exception: the EXDOS 2.0 randomly report data errors on standard machines, it is need a faster CPU. Functionaly this version same with the 1.2 only some I/O timings changed. I guess this version developed for the "Super EP" which is have a Hitachi Super Z80, but it is never released only some news talking about it.)

Offline jltursan

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Re: HW problems/repair
« Reply #18 on: 2013.December.07. 18:06:15 »
So seems the EP64 is slighty more sensible to timings than its big brother EP128. The 200ns EPROM worked fine in the last one.

Also, stupid me, I've checked the 28C256 EEPROM and its pinout is different than the 27C256 one :oops:. Maybe later I'll try to make the pin swapping needed to make it run.

Now, I'll try to upgrade to 1MB Saint's 512KB expansion :ds_icon_cheesygrin:

Offline geco

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Re: HW problems/repair
« Reply #19 on: 2013.December.07. 19:46:17 »
Congratulation :smt041