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Author Topic: EP64/128 expansion port no longer working (Read 4968 times)

Offline Witchy

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EP64/128 expansion port no longer working
« on: 2016.June.16. 23:54:29 »
Hi folks,

I've dug out all my EP stuff again after FAR too many years and I'm sadly not surprised to see some things have failed given the age of the components. Thanks to this forum (hi Zozo :ds_icon_cheesygrin:  ) I've already fixed a video problem with my main ep64 and the ep128 came back to life by itself so I'm expecting that one to fail again soon, probably dried out capacitors.

Main issue I have at the minute is none of my expansion boards work any more and I'm trying to find the common problem between them all. I have at least 2 EXDOS modules, the original Spectrum Emulator and 3 bridge boards but none of them seem to work any more and I can't remember the mechanism that detects the expansion board.

Voltages are OK and the bridgeboard's 7805 is generating +5V for the expansion boxes. I haven't dared to open the EXDOS modules as they're still 'as new' but if they have died over time I'm going to have to. I'm using the same Spectrum+2 PSU I did last time all this kit was at an exhibition in 2005.

Thinking about it I also have a couple of old prototype HDD cards, I'll dig those out too.

Any clues?

Cheers!

Offline Zozosoft

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Re: EP64/128 expansion port no longer working
« Reply #1 on: 2016.June.17. 00:29:09 »
Hi! Welcome on the forum!

You are from http://www.binarydinosaurs.co.uk/ ? Then we mailed lot of many years ago :-)

Firstly I suggest clean all contacts (even if not look dirty).

And my tactics for plug in: firstly plug the Brige to the card, and see from bottom the pins going on the right way.
Then try to plug to the machine.

The original English Bridges (grey) are better than the Hungarian ones (black).

In the machine possible the motherboard little moved (especcialy when disassembled it for the repair) in the case then the connection will misaligned.
It is can be best viewed if the machine top removed.

And you are tried on various machines? I have some motherboards which have a problem with expansions :-(

If EXDOS connected then try this:
10 for i=0 to 7
20 print speek(32,i)
30 next

This print the first bytes of the EPROM, if only 255 printed the something very bad.

The cards are worked previously?

"I also have a couple of old prototype HDD cards, I'll dig those out too."
We talked some businiess about one of these and some other EP stuff, for a TVC configuration :oops:



Offline Witchy

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Re: EP64/128 expansion port no longer working
« Reply #2 on: 2016.June.17. 01:53:19 »
Hi Zozo,

Nice to be back!

I remember the TVC, I recently found the pictures you sent all those years ago when I was clearing up the hard drive of my webserver and realised that machine would be long gone by now. September 2008 that was.... From the hardware summary it was closer to a Camputers Lynx than an EP? Still a nice looking machine though :)

The last exhibition I did was in Croydon UK 2005, the EPs I had on show were put in their box and not opened again until last month, nice to see the flashing ENTERPRISE screen again! You're onto something with the contacts, with the case of a UK bridge removed and the top of the EP shifted slightly I got the nice pause while it looked for a floppy then :help showed EXDOS :mrgreen:

So I put everything back together again and....nothing. Tomorrow I'll shift the motherboard slightly and try the Hungarian bridge again, according to my pictures that's how I ran it back then so fingers crossed. I'm wary of messing with this particular EP128 since it's one of the original factory upgraded 64s.

Cheers!

Offline Zozosoft

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Re: EP64/128 expansion port no longer working
« Reply #3 on: 2016.June.17. 09:50:28 »
I remember the TVC, I recently found the pictures you sent all those years ago when I was clearing up the hard drive of my webserver and realised that machine would be long gone by now. September 2008 that was....
It is still waiting for you!

Quote
From the hardware summary it was closer to a Camputers Lynx than an EP?
Yes, if you think about the 6845.
From software side very similar to the EP, because Bruce Tanner wrote both BASIC, and the OS and DOS also created from the Enterprise versions (downgraded :-) ).


Quote
nice to see the flashing ENTERPRISE screen again!
Yes! :ds_icon_cheesygrin:

Quote
You're onto something with the contacts, with the case of a UK bridge removed and the top of the EP shifted slightly I got the nice pause while it looked for a floppy then :help showed EXDOS :mrgreen:
Great! Then I think no any serious problem. Just need to find the right position. Contacts cleared?

Offline Witchy

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Re: EP64/128 expansion port no longer working
« Reply #4 on: 2016.June.17. 18:38:56 »
Quote
It is still waiting for you!

Really? Wow!

Quote
Great! Then I think no any serious problem. Just need to find the right position. Contacts cleared?

Not yet, that's the plan for tonight, I'm also hoping the board will shift by 1mm or so and that will be enough. I still haven't perfected a method of re-inserting the keyboard ribbon cables without fear of damage.

W

Offline Zozosoft

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Re: EP64/128 expansion port no longer working
« Reply #5 on: 2016.June.17. 18:45:53 »
I still haven't perfected a method of re-inserting the keyboard ribbon cables without fear of damage.
After the first 20-30 time you can do with closed eyes :ds_icon_cheesygrin:

Offline Witchy

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Re: EP64/128 expansion port no longer working
« Reply #6 on: 2016.June.17. 23:24:11 »
OK, I can't get consistency out of the 128 unless I have the top cover off which makes plugging the keyboard in awkward. I've also discovered whilst trying to load things off floppy that the bottom left row of keys doesn't work which means a fault on the right-hand keyboard connector which LOOKS fine. New membrane time?

Time to get out the unused 128 and see if it works as it should; be interesting to see if the bridge will work without its case off!

Offline Witchy

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Re: EP64/128 expansion port no longer working
« Reply #7 on: 2016.June.18. 01:03:14 »
Quote
Time to get out the unused 128 and see if it works as it should; be interesting to see if the bridge will work without its case off!

answer: yes. And I can read most of my floppies. But the screen has started waving which I assume is the C9 capacitor drying out? It'll feel weird fixing a machine that never got used :roll:

Offline Bagpuss22

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Re: EP64/128 expansion port no longer working
« Reply #8 on: 2016.June.18. 02:35:00 »
Hello matey,

Nice to see you on here!  Time to get them EPs working!

If they are original membranes then time for a shiny new one! :)

R

Offline Witchy

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Re: EP64/128 expansion port no longer working
« Reply #9 on: 2016.June.18. 11:36:02 »
Morning Mr P,

I'm on it, always loathed to break open the serial number sticker on a brand old machine but needs must today I think. I'm also wondering why my trusty stalwart 128 won't work with disks unless it's in bits but that's the one that needs the new membrane. I'd steal the membrane from the loose 64 but I've already snipped that one once.

Heh, if one of my non-modded Speccies breaks a membrane I just grab another one off the pile :ds_icon_cheesygrin:

Feels good to be back!

Offline Zozosoft

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Re: EP64/128 expansion port no longer working
« Reply #10 on: 2016.June.18. 17:02:16 »
I'd steal the membrane from the loose 64 but I've already snipped that one once.
You can buy new membranes here.

Offline Witchy

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Re: EP64/128 expansion port no longer working
« Reply #11 on: 2016.June.18. 18:03:33 »
I know; that's open on another tab in Safari ;)

If swapping C9 doesn't cure the wavy screen on the unopened 'new' 128 I'll get one of Rich's membranes for the old exhibition-weary 128...

Offline Zozosoft

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Re: EP64/128 expansion port no longer working
« Reply #12 on: 2016.June.22. 21:26:21 »
Is any news?

Offline Witchy

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Re: EP64/128 expansion port no longer working
« Reply #13 on: 2016.June.23. 02:18:09 »
No, I found my box of Oric Atmos bits including the Cumana floppy interface and a bunch of disks so I've been finding out how many failures I can get with 5 Orics. I can load games OK now via a tap2wav converter running on an old win98 machine I've just built today so back to the EP tomorrow! I've discovered the TOSEC haul of all things Enterprise also in TAP format so if nothing else I can do the same trick with either the 64 or 128.

A

Offline Witchy

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Re: EP64/128 expansion port no longer working
« Reply #14 on: 2016.June.25. 20:28:34 »
OK, finally time to look at this board and straight away noticed that TR4 will wobble the screen when touched or tapped. Standard 3904 or so it seems. The soldering looked well dodgy:

15926-0

so I reflowed it. Still the same. Rummage in my bits box and find another 3904 but I get full-on wobble with that one in place. Odd. Put original back in and it's fine until it's tapped (or, I guess, heats up in use). Find a spare EP64 board that's previously been robbed of bits and use TR4 from that, still the same screen breakdown. Put original back in and all is good so over to the transistor tester.

Original as seen in the pic: hFE 213, Vf 718mV
Replacement from spare board: hFE 433, Vf 674mV

Both 3904s so why the big difference?

W