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Author Topic: Broken EP (Read 11554 times)

Online Zozosoft

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Re: Broken EP
« Reply #15 on: 2014.February.27. 14:47:16 »
Try to start normaly with EXOS, and if you press keys then hear keyboard clicks in headphones? If yes then the machine started just problem with video output and internal speaker. If no then probably problem with the video RAM accessing. And if no right LPT table for the Nick then it is display just garbage which are "no signal" on modern TV.

Offline Saint

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Re: Broken EP
« Reply #16 on: 2014.February.27. 15:07:07 »
Quote from: Zozosoft
Try to start normaly with EXOS, and if you press keys then hear keyboard clicks in headphones? If yes then the machine started just problem with video output and internal speaker. If no then probably problem with the video RAM accessing. And if no right LPT table for the Nick then it is display just garbage which are "no signal" on modern TV.
I dug out an old TV. The video output is one scanline of either white or a selection of colours, then around 60-odd of black. If I tap reset continuously it just gives coloured bars. Is this the test pattern from the ROM?

Resetting with the normal ROM in place I get pretty random crap on the screen ranging from lines to full screens of crap. Just down to how the LPT is setup and how quickly it repeats I guess.

Does this point to bad RAM?
« Last Edit: 2014.February.27. 15:15:46 by Saint »

Online Zozosoft

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Re: Broken EP
« Reply #17 on: 2014.February.27. 15:22:09 »
Yes the Beep test also setting the border color, white when silence, and coloring when beeping.

Online Zozosoft

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Re: Broken EP
« Reply #18 on: 2014.February.27. 15:32:35 »
Quote from: Saint
Does this point to bad RAM?
Yes accessing problem with the onboard memory are the main suspect.
RAM chips, CPU, or the bridge chips (U5,6,7) between the Z80 and Nick bus also are possible.

The Beep test write 00h, FFh, 55h, AAh to the FFh segment, starting the 0. address then continue with the next bytes. You can hear the readed value: low sound are 0 bit, high sound 1 bit.

Offline Saint

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Re: Broken EP
« Reply #19 on: 2014.February.27. 15:57:27 »
Quote from: Zozosoft
Yes accessing problem with the onboard memory are the main suspect.
RAM chips, CPU, or the bridge chips (U5,6,7) between the Z80 and Nick bus also are possible.

The Beep test write 00h, FFh, 55h, AAh to the FFh segment, starting the 0. address then continue with the next bytes. You can hear the readed value: low sound are 0 bit, high sound 1 bit.
Ok, so I hear --

00000000
11111111
10101010
01010101


So it looks like Z80 is reading / writing RAM ok?

So points to Nick not reading from RAM?

Online Zozosoft

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Re: Broken EP
« Reply #20 on: 2014.February.27. 16:12:04 »
Quote from: Saint
So it looks like Z80 is reading / writing RAM ok?
It is looks good.

I think now try the previously uploaded TESZT.ROM
In normal situation display something similar:

Online Zozosoft

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Re: Broken EP
« Reply #21 on: 2014.February.27. 16:49:36 »
Quote from: fatbob_gb
Also the 64 has a broken coil, any idea where I might get a replacement?.
It is a transformer. I not have other idea than remove from other dead motherboard :-(
Alternative way: buy a 5V to 12V DC-DC converter (Step Up) module and replace the entire 12V generator circuit.

Offline Saint

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Re: Broken EP
« Reply #22 on: 2014.February.27. 17:24:19 »
Quote from: Zozosoft
It is looks good.

I think now try the previously uploaded TESZT.ROM
In normal situation display something similar:
Ok, that works well. I have a picture and the internal speaker is working. I think it must be disabled in the version in the 2.4. :)

It is now beeping away and slowing filling the screen wth "*"'s...

Is each * a good byte?

Offline Saint

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Re: Broken EP
« Reply #23 on: 2014.February.27. 19:07:11 »
What's the difference between the 2.4 ROM beep test and the TESZT.ROM? Wondering why I get a good picture with the one ROM and not the other...

Online Zozosoft

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Re: Broken EP
« Reply #24 on: 2014.February.27. 19:10:38 »
Quote from: Saint
Ok, that works well. I have a picture and the internal speaker is working. I think it must be disabled in the version in the 2.4. :)
I will check it :oops:

Quote
It is now beeping away and slowing filling the screen wth "*"'s...

Is each * a good byte?
Yes it looks good.
Then very strange why the EXOS doesn't start...
I think you should check your EXOS EPROM. If it is good then there are probably some problems with the address lines. Check the points where you soldered, isn't anything connected accidentally?
« Last Edit: 2014.February.28. 09:32:31 by szipucsu »

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Re: Broken EP
« Reply #25 on: 2014.February.27. 19:18:53 »
Quote from: Saint
What's the difference between the 2.4 ROM beep test and the TESZT.ROM? Wondering why I get a good picture with the one ROM and not the other...
The 2.4 is the same as the TESZTOLD, it doesn't try to initialize the display, the Nick running free as it is powered on. I selected this is because with the forced initialization method (TESZT.ROM) on a many defective machine nothing can be seen, also lost the border color notification.

Now thinking about the next version: it will run for a few bytes without initialisation and then try to make a display.
« Last Edit: 2014.February.28. 09:34:11 by szipucsu »

Offline jltursan

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Re: Broken EP
« Reply #26 on: 2014.February.27. 20:30:16 »
Big whoops! :(

If you have socketed main ICs (Z80, ROM, etc.) you can try them in your other EP (do you have a another EP right?). The Z80 is most probably working good; but ROM must be zapped. It does no good to reverse all the caps!

Offline Saint

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Re: Broken EP
« Reply #27 on: 2014.February.27. 22:56:15 »
Quote from: Zozosoft
The 2.4 are same with the TESZTOLD, it is don't try initialize the display, the Nick running free as it is powered on. I selected this is because with the forced initialization method (TESZT.ROM) on a many defective machine don't see anything, also lost the border color notification.

Now thinking about next version: it is will run for a few bytes without initialisation and then try to make a display.
I tried the EXOS ROM from my other Enterprise, and now it is working. At least, I get the Enterprise logo flashing on my screen. Many thanks for your help tracking this down Zozo, you have been invaluable help as always! :) 

So reversing the caps must have damaged the EPROM in some way. I'm just blanking it and will see if its still usable, if not then it's the easiest part in the Enterprise to replace, so I've been very lucky... :ds_icon_cheesygrin:

Hopefully with the new set of caps (installed the right way round) EXDOS will work with this EP and I can then start my SD card prototype. I am going to do a wired prototype on a eurocard first this time...

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Re: Broken EP
« Reply #28 on: 2014.February.27. 23:15:42 »
Quote from: Saint
I tried the EXOS ROM from my other Enterprise, and now it is working. At least, I get the Enterprise logo flashing on my screen.
Very good news!

Offline Saint

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Re: Broken EP
« Reply #29 on: 2014.February.28. 00:15:54 »
Hmm, I can boot the EXOS ROM from my old EP64, but cant use the 2.4 ROM. I tried blanking and reprogramming the EPROM, same problem with not booting. I tried another EPROM, same problem. But still the old EXOS boots fine.

Is this a memory paging problem? Really strange.