Enterprise Forever

:UK => Hardware => Maintenance => Topic started by: Saint on 2014.February.26. 23:50:54

Title: Broken EP
Post by: Saint on 2014.February.26. 23:50:54
Ooops, I seem to have broken my Arabic Enterprise. :oops:

I replaced the caps, powered it up, didn't get a picture. Then I compared against my working EP and found I had managed to install the radial caps backwards with negative at the marked end on the PCB. So I switched them all around so that the positive end is at the mark on the PCB, but still no picture.

Wondering what I can have buggered. :roll:
Title: Re: Broken EP
Post by: Zozosoft on 2014.February.26. 23:56:30
I think you least killed the caps... using new ones for the second try?
Title: Re: Broken EP
Post by: Saint on 2014.February.27. 00:02:10
Quote from: Zozosoft
I think you least killed the caps... using new ones for the second try?
I used the same caps and flipped them hoping not to have killed them. I have spares, so I'll replace them all again tomorrow with new ones. :oops:

Weirdly I had managed to install C9 backwards when I first fixed this Enterprise (which is why I copied the polarity for the rest of the caps), so I'm surprised it has been running!
Title: Re: Broken EP
Post by: Zozosoft on 2014.February.27. 00:13:39
Quote from: Saint
I used the same caps and flipped them hoping not to have killed them.
If you have a capacity meter you can check it.
But as I know the electric capacitor doesn't like the reverse polarity. Can explode... (http://www.youtube.com/watch?v=D-RZ5RTAdSg)

Quote
Weirdly I had managed to install C9 backwards when I first fixed this Enterprise (which is why I copied the polarity for the rest of the caps), so I'm surprised it has been running!
:shock: :shock: :shock:
Very mystic!
Title: Re: Broken EP
Post by: fatbob_gb on 2014.February.27. 09:52:39
Do you have UK part numbers for the caps - I have a couple of Enterprises (a newly acquired 64 and my old 128) that have broken 12v lines and very dodgy looking caps throughout. Also the 64 has a broken coil, any idea where I might get a replacement?.
Title: Re: Broken EP
Post by: Saint on 2014.February.27. 10:31:42
Replaced all the caps again with new, still black screen. :evil:

Oh dear, I'm not sure what I've broken or where to even start looking at the moment.


I got my replacement caps from eBay (and TR2 transistor), although not these exact links... 

10uf 35v (http://www.ebay.co.uk/itm/20-pcs-10uf-35V-AXIAL-ALUMINUM-ELECTROLYTIC-CAPACITORS-TVX1V100MAA-NICHICON-/111220444781?pt=LH_DefaultDomain_0&hash=item19e5414e6d)
100uf 25v (http://www.ebay.co.uk/itm/General-Purpose-Radial-Electrolytic-Capacitors-packs-of-10-/290965920308?pt=UK_BOI_Electrical_Components_Supplies_ET&var=&hash=item43beeb9a34)
etc..

Easy enough to match up.
Title: Re: Broken EP
Post by: Saint on 2014.February.27. 10:44:01
Is there some kind of test ROM Zozo which beeps with the internal speaker? Wondering if there was an easy way to see if it was actually running to any degree but with dead video...
Title: Re: Broken EP
Post by: Zozosoft on 2014.February.27. 10:55:15
Quote from: Saint
Is there some kind of test ROM Zozo which beeps with the internal speaker? Wondering if there was an easy way to see if it was actually running to any degree but with dead video...
It is included in the EXOS 2.4, just press down the B key when power on.
Or put the Test ROM segment to segment 00h: if you use 64K EXOS 2.4 EPROM just remove A15 from pin 1 and put back VCC.
Or program the Test rom to separate 16K EPROM, it is at 8000h-BFFFh in the EXOS 2.4 file.

Or there is the original stand alone versions. The OLD just testing, another try to initialize video: copy LPT table and character set to video memory, set up 40 characters mode, and memory testing run in display memory, you can see the caharcter changes during test. It is also beeping.
Title: Re: Broken EP
Post by: Zozosoft on 2014.February.27. 10:57:00
Quote from: Saint
I'm not sure what I've broken or where to even start looking at the moment.
Firstly: now all voltages are ok?
For the next: do you have a oscilloscope or least TTL Logic probe?
Title: Re: Broken EP
Post by: Saint on 2014.February.27. 11:05:34
Quote from: Zozosoft
Firstly: now all voltages are ok?
For the next: do you have a oscilloscope or least TTL Logic probe?
Ok, I'll try connecting VCC to A15 on the 2.4 ROM and see what happens. It's difficult to tell with modern TV's what is going on, as you may have some messed up video output, but unless the TV recognises it as a valid format, it just says no signal. Not useful for debugging!!

Yes, I have an oscilloscope and logic sniffer. I was wondering where to start... see if the Z80 bus is active?
Title: Re: Broken EP
Post by: Zozosoft on 2014.February.27. 11:28:10
Quote from: Saint
Ok, I'll try connecting VCC to A15 on the 2.4 ROM and see what happens. It's difficult to tell with modern TV's what is going on, as you may have some messed up video output, but unless the TV recognises it as a valid format, it just says no signal. Not useful for debugging!!
Keep a old good CRT monitor for a service work :-) Philips CM8833 or a similar.

Quote
Yes, I have an oscilloscope and logic sniffer. I was wondering where to start... see if the Z80 bus is active?
- check the System Clock at U18 pin 12 (8MHz)
- check Z80 Clock at Z80 pin 6 (4MHz)
- check Video Clock at U37 pin 10 (14.237536 MHz)
- check Reset signal on Z80 pin 26 while pressing reset button. One impulse needed for each pressing.
- check 1MHz Clock at expansion bus pin A21
If no reset and no 1MHz then the Dave not running probably it is dead :-(
For the video part check VCAS and VRAS on video RAM ICs (pin 15 and pin 4) and VMUX on U8,9 pin1. These are cyclic signals because the Nick always reading video memory. If no activity then Nick not running...
If these good then check RD, MREQ and M1 signal at Z80 (pin 21,19,27), if all do activity then CPU looks running. Then check ROM CE signal at EPROM pin 20. (I found few partialy dead Dave chips which are not generate ROM or CART signal, this is can be substitued by adding one address decoder IC)
Title: Re: Broken EP
Post by: Zozosoft on 2014.February.27. 11:33:16
One note for BEEP testing: plug a speakers/headphones to Tape Out (Stereo Output) connector for the case if internal speaker circuit dead.
Title: Re: Broken EP
Post by: Saint on 2014.February.27. 11:39:28
Quote from: Zozosoft
Keep a old good CRT monitor for a service work :-) Philips CM8833 or a similar.
- check the System Clock at U18 pin 12 (8MHz)
- check Z80 Clock at Z80 pin 6 (4MHz)
- check Video Clock at U37 pin 10 (14.237536 MHz)
- check Reset signal on Z80 pin 26 while pressing reset button. One impulse needed for each pressing.
- check 1MHz Clock at expansion bus pin A21
If no reset and no 1MHz then the Dave not running probably it is dead :-(
For the video part check VCAS and VRAS on video RAM ICs (pin 15 and pin 4) and VMUX on U8,9 pin1. These are cyclic signals because the Nick always reading video memory. If no activity then Nick not running...
If these good then check RD, MREQ and M1 signal at Z80 (pin 21,19,27), if all do activity then CPU looks running. Then check ROM CE signal at EPROM pin 20. (I found few partialy dead Dave chips which are not generate ROM or CART signal, this is can be substitued by adding one address decoder IC)
I have a nice Atari SC1224 which would do the trick, but no cable for the EP. Would be handy to have one right now! :)

I've connect VCC to A15, nothing on the speaker, but I do have beeps on the headphones. I assume this is bad? :cry:

I will get the oscilloscope out and check those signals, thanks for the list. One other thing is I was missing one new cap, so C24 is an old possibly dead one.
Title: Re: Broken EP
Post by: Zozosoft on 2014.February.27. 11:52:04
Quote from: Saint
I've connect VCC to A15, nothing on the speaker, but I do have beeps on the headphones. I assume this is bad? :cry:
It is good because least partialy working the machine :-)
Title: Re: Broken EP
Post by: Saint on 2014.February.27. 14:32:16
Quote from: Zozosoft
It is good because least partialy working the machine :-)
It's not looking too bad so far...

Video Clock at U37 pin 10 is present
VCAS and VRAS activity
VMUX signals present
csync at 15khz
peritel mode switch 12v (10v with scart connected)
activity on RGB lines


But no signal on digital TV. So it looks like the signal isn't constant enough for the TV to accept.
Title: Re: Broken EP
Post by: Zozosoft 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.
Title: Re: Broken EP
Post by: Saint 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?
Title: Re: Broken EP
Post by: Zozosoft on 2014.February.27. 15:22:09
Yes the Beep test also setting the border color, white when silence, and coloring when beeping.
Title: Re: Broken EP
Post by: Zozosoft 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.
Title: Re: Broken EP
Post by: Saint 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?
Title: Re: Broken EP
Post by: Zozosoft 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:
Title: Re: Broken EP
Post by: Zozosoft 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.
Title: Re: Broken EP
Post by: Saint 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?
Title: Re: Broken EP
Post by: Saint 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...
Title: Re: Broken EP
Post by: Zozosoft 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?
Title: Re: Broken EP
Post by: Zozosoft 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.
Title: Re: Broken EP
Post by: jltursan 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!
Title: Re: Broken EP
Post by: Saint 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...
Title: Re: Broken EP
Post by: Zozosoft 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!
Title: Re: Broken EP
Post by: Saint 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.
Title: Re: Broken EP
Post by: Zozosoft on 2014.February.28. 00:32:09
Have you put back the A15 address line to pin 1 instead of the VCC?
Title: Re: Broken EP
Post by: Saint on 2014.February.28. 08:13:28
You putted back the A15 address line to pin 1 instead the VCC?

Yes :)

Seems really strange.

Memory paging must be working as the old EXOS ROM goes through the memory test fine. The beep test with a15 set to vcc also does the same odd screen scan lines. This is just making the 27512 act like a 27256 with the beep test rom, so I don't understand. It's like having the 27512 eprom in there is causing the problem...

I'll try reprogramming the 27512 with just the beep test rom image I know is working on the 27256. This should tell us if the actual eprom is the problem.
Title: Re: Broken EP
Post by: Zozosoft on 2014.February.28. 09:05:06
Quote from: Saint
Memory paging must be working as the old EXOS ROM goes through the memory test fine.
But it cannot detect if whole segments are overwritten because of address line problems.
There is the stand alone version of my memory test for cartridge use with original EXOS 2.0/2.1
It is needed to put the lowest page of the cartridge (04h segment), the EXOS call there external testing program. Try to use this with original EXOS ROM.
Title: Re: Broken EP
Post by: Zozosoft on 2014.February.28. 09:10:33
Another idea if the cartridge works.
Put monitor program to cartridge, ASMON or FENAS. Then you can page segments and view contents.
Program EXOS 2.1 to 27C512 low part, and for the high segments some text, for example "this is the segment 02h", and 03h to another.
If the machine started then view in monitor program what you see in segment 02 and 03. if you see the EXOS ROM instead the texts then the A15 stuck as 0.
If the machine does not start, try EXOS to the high part, and texts to the low (now are 00 and 01 segments)
If the machine started with this very strange ROM then the A15 stuck as 1...
Title: Re: Broken EP
Post by: Zozosoft on 2014.February.28. 09:19:02
Some note, not a good news for you :-(
I have some machines with partially defective Dave chips, some of the address lines not working. For example only 1MB address space can be handled insted 4MB, the 1MB space mirrored as 4 times. It this situation the high address lines are defective :-(
But the A15 on system bus also come from the Dave.

In the deffective lines I see instead the right 0/1: floating/1. I thinkig about using transistor or anything convert this to the right 0/1.
Title: Re: Broken EP
Post by: Saint on 2014.February.28. 10:04:41
I burnt an EPROM with the beep test at slot 3 on the 27512 and installed with A15=vcc. Worked fine.

Next, I thought I would check A15 with the scope to see what activity there was. I looked at the expansion connector and found the wire which runs A15 to the 2.4 EPROM had come un-soldered. It was glued in place so it looked fine, but the connection had broken away! :oops:

It must have happened while I was handling the PCB de/soldering all the caps. So after all that, it looks like putting the caps in backwards didn't break anything. Phew! It was just me knocking a wire out. :oops:

Hehe, all good news and some fun experience tracking down what was wrong. There are actually 3 more caps to replace next to the modulator / power, then I have a fully electrolytic re-capped  machine.

I hope some more non-working EP's come up on eBay, I think I could get the hang of repairing them with all of Zozo's tips in this thread alone... :)
Title: Re: Broken EP
Post by: Zozosoft on 2014.February.28. 11:29:40
Then now everything working?
Title: Re: Broken EP
Post by: jltursan on 2014.February.28. 19:04:52
If so, excellent work all in all :smt038
Title: Re: Broken EP
Post by: Saint on 2014.February.28. 20:10:21
Yes, all working now! I even tidied up the hack someone had done on the cap / resistor layout on the modulator. They seem to have copied the setup in the Issue 1 motherboard, where the Issue 5 tidied it up a bit.

And also thanks to jltursan, as I checked my EXDOS and replaced with 150ns EPROM (I had a 250ns EPROM in there!) and now it boots with the Arabic Issue 5 Enterprise. Funny as the 250ns EPROM booted fine on my old Issue 1 Enterprise!

Thank you all, I now feel happy that my "test" Enterprise is working and I can make a start on the SD card interface prototype. :)
Title: Re: Broken EP
Post by: Zozosoft on 2014.February.28. 20:36:06
Issue 1??? Are yoy sure about this? If i remember right your other machine are EP128. These are usualy ISSUE 6. Few machines are ISSUE 4.
Title: Re: Broken EP
Post by: jltursan on 2014.February.28. 21:12:26
Double yay! (both for having repaired the EP and for the SD project :mrgreen:). 

Maybe the 150ns EPROM has definitely something to do with the Dave speed as Zozo has already pointed out :?:
Title: Re: Broken EP
Post by: Saint on 2014.February.28. 22:08:07
Quote from: Zozosoft
Issue 1??? Are yoy sure about this? If i remember right your other machine are EP128. These are usualy ISSUE 6. Few machines are ISSUE 4.
Sorry, my old EP64 is Issue 4. Not sure where I got 1 from. :oops:

The Arabic EP64 is Issue 5.
Title: Re: Broken EP
Post by: Zozosoft on 2014.February.28. 22:25:05
Can you post photos both Dave chips?
One idea: try to measure the delay from MREQ to Eprom CE on the EXDOS card with both machine. CE generated by using the high address lines from the Dave. If one Dave slower then more delay at the CE.
Title: Re: Broken EP
Post by: Saint on 2014.March.01. 14:43:13
I will get some photos of the two Dave chips later on today if I get a chance!

Here we go... First is Issue 5 pcb and second is issue 4.

Title: Re: Broken EP
Post by: Zozosoft on 2014.March.02. 20:21:13
Interesting the different oriented texts! Anyway it is look same, just the date code different. But it is sure these are come from different batch of chips.
The first is which have a problem with the slower EXDOS EPROM?

Jltursan! If I remember right you found same problem about EXDOS EPROM speed? Can you post photos of your Dave chips?

I will look around at my spare machines about can I reproduce this problem?
Anyway I always suggested using least 150ns fast EPROMs. But will be interesting if can be found slower Dave chips, it is can be affect the overclocking ability?
Title: Re: Broken EP
Post by: Saint on 2014.March.02. 22:26:52
Quote from: Zozosoft
Interesting the different oriented texts! Anyway it is look same, just the date code different. But it is sure these are come from different batch of chips.
The first is which have a problem with the slower EXDOS EPROM?

Jltursan! If I remember right you found same problem about EXDOS EPROM speed? Can you post photos of your Dave chips?

I will look around at my spare machines about can I reproduce this problem?
Anyway I always suggested using least 150ns fast EPROMs. But will be interesting if can be found slower Dave chips, it is can be affect the overclocking ability?
Yes, the Issue 5 is the one with the problem with slower EPROMS. It is odd the text is put on at a different angle between the chips... :)

The older Dave will run with 250ns EPROMS in EXDOS. But also, I put the old beep test image onto a 250ns EPROM and this ran ok from the motherboard socket of the Issue 5 board.
Title: Re: Broken EP
Post by: jltursan on 2014.March.02. 22:38:04
Yep, along the next week I'll try to open the EPs and take some photos of their Dave ICs.

I suposse its an issue related to the EXDOS card itself or the expansion bus. I'm sure I've also used slower EPROMs in the motherboard socket without flaws.
Title: Re: Broken EP
Post by: Zozosoft on 2014.March.02. 22:44:11
Quote from: Saint
 But also, I put the old beep test image onto a 250ns EPROM and this ran ok from the motherboard socket of the Issue 5 board.
It is not a surprise, because the internal ROM (and the cartridge) have a faster enable signal directly from the Dave. On the EXDOS card many additional 74LS logic ICs used for the address decoding, these are many more nanoseconds.
Title: Re: Broken EP
Post by: SlashNet on 2014.March.07. 11:43:51
Hello.

One member, from zx.pk.ru forum, trying to repair his EP 128k (he don't speak english).

He made some videos. What can you say about that problem?
Where to look first?

Videos:
https://www.dropbox.com/s/r1i2rjukv35zvaj/break_enterprise.zip
Title: Re: Broken EP
Post by: Zozosoft on 2014.March.07. 11:57:12
Quote from: SlashNet
He made some videos. What can you say about that problem?
Where to look first?
It looks the common "no 12V" problem.
Check it at U35 (LM1889) Pin 14,15,16.
If no 12V then replace TR2 (BC337). And probably the C9 capacitor dried out this killed the transistor. It is a good idea to replace it too.

Keyboard membrane tails need some cutting.
Title: Re: Broken EP
Post by: SlashNet on 2014.March.08. 10:20:12
On these pins - +6.5В.
Replacement of TR2 (replaced to C945) did not change anything.
Capacitor C9 in good condition.
Title: Re: Broken EP
Post by: Zozosoft on 2014.March.08. 11:42:08
Ok the problem was what I thought: no 12V
Are C945 fully compatible with BC337? Can't he get BC337? I use BC337-40 type.
Title: Re: Broken EP
Post by: SlashNet on 2014.March.09. 19:24:42
He repaired 12V and all working now. Thanks.

Little bonus: his EP was ordered by advertisement in magazine "Юный техник" (Young Technician) in 1993. Manual on english. SN with additional label "QC passed:"
Title: Re: Broken EP
Post by: Zozosoft on 2014.March.09. 19:49:52
Quote from: SlashNet
He repaired 12V and all working now. Thanks.
Great news!
Title: Re: Broken EP
Post by: SlashNet on 2014.March.31. 20:58:39
Recently noticed that some time after the power on EP, some demo start behaving buggy.
What could it be?
Comp is mine.

http://youtu.be/Us8QcNU5knk
Title: Re: Broken EP
Post by: Zozosoft on 2014.March.31. 21:32:04
Previously you tried to run this demo on this machine?
Title: Re: Broken EP
Post by: SlashNet on 2014.March.31. 21:46:30
Only week ago. Same effects.
Title: Re: Broken EP
Post by: Zozosoft on 2014.April.01. 12:30:46
Then I'm afraid you have the older 08-04 version of Nick chip :-(

Try to run this little BASIC program:
Code: [Select]
  10 GRAPHICS ATTRIBUTE
   20 SET INK RND(16)
   30 PLOT RND(1280),RND(720)
   40 GOTO 20

It is draw a random color pixels, with the buggy version Nick you see some pixels are flashing as the stars on the sky. After the machine (and Nick) heating up then more flashing pixels.
Also good test view interlaced IVIEW picture (from my Interlace Demo 3 package), see this video. (http://enterpriseforever.com/hardver/pixelhibas-alaplapok/?action=dlattach;attach=4068) At the start you see many green and purple flashing pixels, then I placed a cold heatsink to the Nick then the most of the buggy pixels are eliminated.
Another good example the Eat-it-up game, see the video (http://enterpriseforever.com/hardver/pixelhibas-alaplapok/?action=dlattach;attach=4067). Many yellow buggy pixels, which are removed when the Nick cooled.

These are extreme examples with very bad Nick with removed heatsink. In normal situation you can see something wrong pixels but not as bad in these examples.

Also reported other interesting effects with these Nick chips, for example at the Tape Level signal at the status line, when it is green red vertical line can be remain.

The 08-47 revisions Nick chips are don't do these, also running fine without the heatsink. (I verified the temperature of both revisions and are same!)
Originaly no heatsink developed, when the first machines builded then ordered heatsink to Nick. (http://enterprise.iko.hu/historical/Concession%20Note%206.pdf)

If your Nick are 08-04 then you check the Nick heatsink! After the 30 years it is fall in many machines. If this happened when it is glued back then buggy effect are reduced.
If you order memory expansion from Saint then you can put better, bigger heatsink to the Nick :-)

I not tested this specified demo previously but I will run on know 08-04 machines.
Title: Re: Broken EP
Post by: SlashNet on 2014.April.01. 20:55:13
No. I can't see any green flashing dots.
Heatsink was glued fine.
Nick (as I see on marking that was left on heatsink) is 08-47.
Title: Re: Broken EP
Post by: Zozosoft on 2014.April.01. 22:21:20
Quote from: SlashNet
Nick (as I see on marking that was left on heatsink) is 08-47.
Then very interesting! :shock:

Once someone reported crazy screen bugs what I can't reproduce on my machines.
Try the Jack The Nipper:
White line before the title text. (http://enterpriseforever.com/hardver/pixelhibas-alaplapok/?action=dlattach;attach=7598)
And Fast Food:
Screen garbage under loading. (http://enterpriseforever.com/hardver/pixelhibas-alaplapok/?action=dlattach;attach=7588)
And under the game. (http://enterpriseforever.com/hardver/pixelhibas-alaplapok/?action=dlattach;attach=7592)
Title: Re: Broken EP
Post by: SlashNet on 2014.April.01. 23:20:17
First photo looks familiar (sometimes this line flashing) - that I noticed many years ago.
Last two... Maybe, I saw. I'll try tomorrow to load and watch.
Title: Re: Broken EP
Post by: Zozosoft on 2014.April.02. 00:01:25
Quote from: SlashNet
First photo looks familiar (sometimes this line flashing) - that I noticed many years ago.
Who found this say many programs with similar loader (title name under the screen) produce same bug. I'm never see same :oops:

One quick idea, I'm not sure it is change anything: short circuit R12. Usualy we do this when made a turbo machine, this adjust something with the video RAM timing.
Title: Re: Broken EP
Post by: SlashNet on 2014.April.02. 19:20:25
Yep. Fast Food has same effect.

R12 - shorted. Nothing changed.
Title: Re: Broken EP
Post by: Zozosoft on 2014.April.02. 20:04:41
Can you make detailed photos from your motherboard? I will look for a similar one from my spares and test it with these programs.
Title: Re: Broken EP
Post by: SlashNet on 2014.April.02. 20:48:45
Here photogallery: https://www.dropbox.com/sh/oduseq994r1t9s2/atC8Cvyc5-

I don't remove PCB with memory, because I don't have currently soldering-iron to put it back.

Some photos from other side here: https://www.dropbox.com/sh/kckg3wa3inocrub/AgKLQn--Qt
Title: Re: Broken EP
Post by: Zozosoft on 2014.April.02. 21:03:32
Quote from: SlashNet
I don't remove PCB with memory, because I don't have currently soldering-iron to put it back.
Don't problem, I think the CPU, video RAM ICs, memory multiplexers are the most important components about the problem.
This is look exactly same. (http://gafz.enterpriseforever.com/Galery/Alapgep/Picture/EP128_motherboard(03-01)~1.jpg) Now needed to find which machine have this board :oops: I hope not sold these under the many years after this photo made.
Title: Re: Broken EP
Post by: Zozosoft on 2014.April.03. 23:12:03
I found same motherboard but don't see any crazy screen bugs.
It is good new for me :-) But bad news about your problem :-( hard to find what is the problem if I'm not see it .-(
Title: Re: Broken EP
Post by: SlashNet on 2014.April.04. 12:33:48
bad good news, but anyway thanks. :)
Title: Re: Broken EP
Post by: Zozosoft on 2014.April.04. 13:16:55
I will try to make minimum version from the know "bug-generator" programs, for example only keep the LPT and screen build parts. If the minimum programs also make a crazy screen for you, then possible change something or other something, etc for detect which Nick settings generate bugs. If we know the specified settings then can thinking about what do this in hw level.

But it is will be later, I'm currently busy about the SD Cartridge software :oops:
Title: Re: Broken EP
Post by: SlashNet on 2014.April.04. 15:35:26
OK.
It's not so urgent :)