Enterprise Forever
:UK => Hardware => Maintenance => Topic started by: munchausen on 2014.July.29. 10:35:58
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Hi everyone,
I recently came across an enterprise 128 sold as non-working. It seemed a fair gamble, so I got it home and have discovered it has a number of parts missing from the PCB. They mostly seem to be power related, it looks like whoever did it didn't really know what they are doing because they even removed many easy to find parts, so I hope that Nick and Dave are OK.
The parts missing are:
U19, U20, U21, D2, D3, D4, C8, C9, C10, C11, C12, TR2, TR3, R13, R14, R15, R16, R202, L1 and the RF/UHF modulator
From looking at the back of the PCB it seems that L2 has also been attacked (I have to say attacked, because whoever did this has very little competency... many tracks have been destroyed) and maybe U18 as well.
Most of the parts are relatively easy for me to replace, and the track damage does not look impossible either. However, there are some parts that I don't know how I will find: does anyone know the value of L1 or a suitable replacement? It looks like a complex part (5 pins). A replacement for L2 might also be useful. R202 looks like it might be hard to find a replacement for also, though it might be possible to replace it with a pair of fixed resistors if I can figure out good values for them. Since the RF modulator is missing I will probably just put a composite video connector in its place.
There are also other issues - both keyboard ribbon cables have had the ends cut off, there is a key missing (the "<>" key to the right of the left shift), the transparent plastic cover above the function keys is missing, the speaker has been removed, the space bar does not press down, the joystick top is missing and someone has for some reason used a knife to scratch into both the top and bottom of the case (on the outside) "Serial No 007101".
So the poor enterprise has received a lot of abuse :(. I do hope I can get it working, I have always found the enterprise a very interesting machine but could not afford a fully working one.
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Have you seen the schematics here (http://enterprise.iko.hu/schematics.htm).
I had en ep64 that needed the power circuit repaired - it worked out easier to remove the lot and use modern parts to generate the 12v line.
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Hi, yes I've looked at the schematics and there is no value for L1, I'm not certain about L2 (I didn't find it yet) but I suspect that will also be missing. Even a part number might be handy for finding out what it is, but a suitable replacement part would be even better - any info is appreciated!
Replacing the power circuit completely would be OK I guess, but I don't fully appreciate how sensitive it is or how to address that... I could easily stick a couple of 7805s and a 7812 on there, but I guess you need some sort of filtering because that presumably is the function of the transistors, coils and other extra parts?
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it worked out easier to remove the lot
As I see someone do this part of the work :-)
and use modern parts to generate the 12v line.
Yes, mainly because the L1 missing... it only can be replaced from another broken Enterprise. Don't know it is specifications :-(
I suggest firstly repair the +5V circuits, and check Z80, Nick, Dave activity. If it is looks working then go ahead with others. Scope are good help :-)
RF modulator are same with Spectrum, ZX81, etc I think not too hard find it. But it is a very poor picture quality, more better idea make a RGB SCART cable :-)
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I'm not certain about L2
It is at left side of the power LED (http://gafz.enterpriseforever.com/Galery/Alapgep/Picture/ISSUE5-4.jpg), it is used fine adjust the Nick clock frq.
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I guess you need some sort of filtering because that presumably is the function of the transistors, coils and other extra parts?
No, the extra parts made about 15-16V AC from the 9V DC power supply, then D4 and U21 made +12V DC from the AC. At today this is called as "Step Up converter", you can found small boards in the Ebay.
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If you build another solution for the +12V then TR2, TR3, R13, R14, R15, R16, C9, C10, L1, D4, U21 not needed, connect your +12V to U21 out pin location.
+12V only used by the two LM18xx ICs.
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Thanks for all the replies :)
I didn't realise it was a step up section. Does anyone know offhand how much power the 12V needs to supply? I have a lot of step up converters from ebay, they claim to be able to supply 1A but I doubt that they can really achieve that at 12V, especially without a heatsink. Presumably if it only powers the LM18xx ICs then it can't be more than a hundred mA or so, I can check the data sheets I guess.
It looks as though you would get a picture from an RGB SCART cable without the 12V line working, is that right?
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It looks as though you would get a picture from an RGB SCART cable without the 12V line working, is that right?
That depends, my Scart cable uses the 12v line to switch the TV into RGB Mode. IIRC I did use the RGB with an old Amstrad RGB monitor when I had a dodgy 12v line and it work OK(ish) - It gave a picture anyway.
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I do have three amstrad monitors so I could give that a go. I don't have the right connector for the mobo though.
Does anyone know of somewhere I can buy a ready made SCART cable? I'm sure I saw some for sale a while ago but I can't find the site now.
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It looks as though you would get a picture from an RGB SCART cable without the 12V line working, is that right?
It is depend about the TV/Monitor type. For example my Samsung TV always switch to computer if the 12V present. If no 12V then can I switch with the AV button to the computer or back to TV mode.
Philips CM8833 monitor also don't need it, its is have a Input button for switch RGB or Composite mode.
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Is any news about the patient?
Do you try to reconstruct the +5V circuits?
The main question: Nick and Dave working? All others can be replaced or substituted.
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No news yet... I have too much to do this week. But on the weekend I will repair the 5V line and add the 12V buck boost. I will also add a composite video output. I don't know if I will be able to sort out a SCART cable as I don't have the parts, so I hope that the composite encoders work. I do have a scope so I should be able to tell if something is happening, anyway.
I am nervous about Nick and Dave, since this enterprise looks as though it has been scavenged for parts it seems likely that one or other of them could be dead. :???:
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I do have a scope so I should be able to tell if something is happening, anyway.
Scope are good friend! :)
After the voltages are ok, check the clock lines, 14.2... Mhz Nick clock, 8Mhz System clock, 4Mhz, Z80 clock, 1Mhz clock output on the expansion bus.
If all ok, check the reset pin at the Z80, if always low then probably Dave dead :cry: if the 1Mhz output are also missing then more possible the Dave dead :smt022
Next step check Z80 activity: RD, MREQ, M1, address lines. If it is look running, then check CE (pin 20) of the ROM chip, if no activity then probably Dave dead... least partialy. I found some Dave chips which are not generate ROM (or CART) signal. This is can be substituted with few 74xxx ICs to generate new ROM signal.
If Z80 running, and accessing ROM then check Nick chip activity.
Nick always reading Video Memory with constant rate, there is some scope pictures:
Video Clock and Video CAS
[attach=1]
Video Clock and Video RAS
[attach=2]
Video Clock and Video MUX
[attach=3]
Video RAS and Video CAS
[attach=4]
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Wow, thanks, this should be very useful. I will keep you updated as to how it goes.
"Dead Dave" reminds me of this (maybe it's come up here before):
http://www.youtube.com/watch?v=shs7VQhVvxA
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Will be the next question: do you have a EPROM programmer?
At most of times if the onboard memory are faulty the original EXOS ROM don't make any life sign. Because it is use a CALL instruction for call the memory testing routine, and if the memory are hardly faulty then the return address are corrupted...
Then I wrote a little test ROM which are don't use any bit of the RAM for the program running. Another problem if the onboard (video) memory are faulty then you can't generate proper screen...
My program wrote bytes to RAM and generate beep sound from the readed bits (low and high sound frq) then you can got some life sign from a machine which are do nothing with the original EXOS ROM.
(This test routine are also included in the EXOS 2.4)
Note: not only faulty RAM chips can make this problem. I found many faulty Z80 CPUs which are make bugs when writing memory. Very interesting these are produced in same factory with close date codes!