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Author Topic: HW problems/repair (Read 2834 times)

Offline jltursan

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HW problems/repair
« on: 2013.December.02. 20:22:07 »
I just want to leave some feedback. I've recently purchased one of the eBay units and it has been -mostly- sucessfully tested, great piece of hardware. Now I'll explain the -mostly-... :)

The expansion has been assembled in a EP64, easy to work as I don't need to desolder the EP128 64KB RAM board. It has been tested fine: EXOS 2.4 tests and even a IS-BASIC program (only the first three or four segments, I was pokeing all the addresses 0-16383!); but...it's extremely unreliable when I plug my EXDOS controller.
Sometimes I can create a RAMDISK; but it shows corrupt info after a couple of DIR commands. I've been able to format a disk; but it corrupts the same way as the RAMDISK after a DIR.

Facts:

- As the original PSU is a bit weak, I've replaced the original CPU by a powerful one with no changes.
- I've tested the EXDOS controller without flaws in the EP128.
- The controller has been upgraded to EXOS 1.3 thus, the 27128 original EPROM has been replaced by a 27256.

I'm starting to think that I'll need to swap the expansions and migrate the 512KB one to the EP128...:roll:

Anyone has a clue about what's happening?

Offline Zozosoft

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Re: HW problems/repair
« Reply #1 on: 2013.December.02. 20:52:08 »
Have you tried the EXOS 2.4 Advanced test when EXDOS attached?
Anyway, a good idea: clean the expansion connector.
« Last Edit: 2013.December.02. 21:07:26 by szipucsu »

Offline Saint

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Re: HW problems/repair
« Reply #2 on: 2013.December.02. 21:47:20 »
Quote from: Zozosoft
Have you tried the EXOS 2.4 Advanced test when EXDOS attached?
Anyway, a good idea: clean the expansion connector.
Yep, I'd definitely try the advanced memory test first up to make sure it's all connected correctly.

I've not been able to test with EXDOS yet, as my EXDOS board is broken. I really need to find the time to take it apart, hook it up and do some tests to find out what is wrong!

I cant think of any reasons why EXDOS itself would cause issues, other than if it caused spikes on the address bus which would be missed by slower RAM. I know there were some issues like this on the Atari ST. The system wasn't very well designed, and the address bus is very noisy. Using faster RAM actually causes problems as it picks up the noise and causes writes to wrong addresses. The slower RAM misses these spikes.

Offline Zozosoft

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Re: HW problems/repair
« Reply #3 on: 2013.December.02. 22:07:48 »
We succesfully using similar 55ns SRAM chips on MICROTEAM EXDOS clone:
10000-0

Working with 4/6/7.12Mhz machine, and the WD also have overclocking circuit for handling HD disks :-) Plus IDE card. This config have 2x512K SRAM, 2x256K DRAM and 1x512K Flash ROM expansion. No any problem.

When the expansions for Hungary arrive to me :oops: then I can test with many different machines and expansions!

Offline Zozosoft

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Re: HW problems/repair
« Reply #4 on: 2013.December.02. 22:17:54 »
jltursan! Before the upgrade you used the EXDOS card with your EP64? It is worked?

One idea: with the EXOS 2.4 you can start the machine in 64K mode. In this mode try to run 64K games. Also good idea copy games from disk to another, and check the copied programs also working? In this situation the memory expansion not used. If any problem detected then possible some problems with the EXDOS connection.

Offline Saint

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Re: HW problems/repair
« Reply #5 on: 2013.December.02. 22:20:53 »
Quote from: Zozosoft
We succesfully using similar 55ns SRAM chips on MICROTEAM EXDOS clone:
(Attachment Link)

Working with 4/6/7.12Mhz machine, and the WD also have overclocking circuit for handling HD disks :-) Plus IDE card. This config have 2x512K SRAM, 2x256K DRAM and 1x512K Flash ROM expansion. No any problem.

When the expansions for Hungary arrive to me :oops: then I can test with many different machines and expansions!
It's good to hear 55ns is working ok! :ds_icon_cheesygrin:

It feels like I have been waiting forever for this batch of PCB's... :(

Offline Zozosoft

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Re: HW problems/repair
« Reply #6 on: 2013.December.02. 22:29:13 »
Quote from: Saint
It feels like I have been waiting forever for this batch of PCB's... :(
Least the GALs arrived?

Offline jltursan

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Re: HW problems/repair
« Reply #7 on: 2013.December.02. 22:42:45 »
Quote
One idea: with the EXOS 2.4 you can start the machine in 64K mode. In this mode try to run 64K games. Also good idea copy games from disk to another, and check the copied programs also working? In this situation the memory expansion not used. If any problem detected then possible some problems with the EXDOS connection.

I like the idea, I'll try this (or even disabling completely the expansion by pulling off the EXP2 connector) ASAP.
To be honest I've been using the EXDOS controller mostly with my EP128. The EP64 is a newcomer and it has suffered a lot, maybe it has still some strange flaws I haven't noticed until now.

Offline Zozosoft

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Re: HW problems/repair
« Reply #8 on: 2013.December.02. 22:57:45 »
Quote from: jltursan
The EP64 is a newcomer and it has suffered a lot, maybe it has still some strange flaws I haven't noticed until now.
Then I suggest thorough cleaning of the expansion connector. The "not used for many-many-many years" connectors can make stability problems, especially on arabic machines which are stored in desert for a long time :-)
Another possible problems with arabic machine the dried out electric capacitors, especially if your board built with PHILIPS capacitors.

Offline jltursan

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Re: HW problems/repair
« Reply #9 on: 2013.December.02. 23:12:16 »
Mmmm, I usually give a good clean to my machines; so I'm confident about it :); but, indeed, working on it I've already replaced a couple of capacitors. I'm starting to think that the machine could need a full recapping :evil:

I've tested the advanced test with the EXDOS plugged and it ran succesfully. Seems that the expansion has nothing to do with my problems. I've totally unplugged Saint's expansion and the EP64 doesn't simply boots with EXDOS controller. It gives a black screen or an endlessly logo boot screen :evil::evil:

To worse things, also, I've noticed that even in the EP128, the EXDOS needs some "heating" to boot properly. I'm so used to it that didn't recall that it usually doesn't work at first boot, it can't even find EXDOS ROM when doing a :help command. After a couple of reboots, it works absolutely fine.

Another recapping victim? :cry:

Offline Saint

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Re: HW problems/repair
« Reply #10 on: 2013.December.03. 10:13:25 »
Quote from: Zozosoft
Least the GALs arrived?
No, still waiting for those as well! Post seems to be very very slow.... :(

I'm glad to hear the memory expansion is not the cause of the EP64 problems, though! I had some odd behaviour with my EXDOS expansion before it stopped working completely, so it sounds like yours needs some attention too, jltursan. I will be interested to hear what your problems are.

Offline Zozosoft

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Re: HW problems/repair
« Reply #11 on: 2013.December.03. 10:25:46 »
Quote from: jltursan
To worse things, also, I've noticed that even in the EP128, the EXDOS needs some "heating" to boot properly. I'm so used to it that didn't recall that it usually doesn't work at first boot, it can't even find EXDOS ROM when doing a :help command. After a couple of reboots, it works absolutely fine.
Very interesting!
Firstly check the +5V on the card, with scope of you have. The 9V to 5V conversion in the system bus bridge.

Other idea: try to put back the original 1.0 EPROM, it is working or also same problems?
Which type of 27256 used for the EXDOS 1.3? I recommend 150ns or faster.

Offline Zozosoft

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Re: HW problems/repair
« Reply #12 on: 2013.December.03. 10:27:58 »
Quote from: Saint
I had some odd behaviour with my EXDOS expansion before it stopped working completely
What happened with your card? EP don't start with the card, or starting but the EXDOS not detected?

Offline Z80System

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Re: HW problems/repair
« Reply #13 on: 2013.December.03. 11:33:00 »
Quote
No, still waiting for those as well! Post seems to be very very slow....
I heard from sellers at ebay, that christmas time is a international transport horror with terrible delays and such things ...
Z80 System

Offline jltursan

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Re: HW problems/repair
« Reply #14 on: 2013.December.03. 22:39:12 »
A quick update...

I've replaced the 100uF electrolityc capacitor if the bridge (and the +5V regulator as a bonus), it was notoriously "inflated". The controller plugged to the EP128 seems to boot more stable now, I'll keep testing to be sure about this.

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.