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wolfman_55
November 19th, 2014, 04:01 AM
Hi All,

Just joined in the hope of some help.

My first computer was a Science of Cambridge MK14, which sadly I don't have any more. My second was a UK101 which I'm now trying to get working. It was heavily based on the Ohio Superboard that was available at the time.

I've replaced three damaged keys (Many thanks RS who still stock them!), sorted out a better 5v PSU and connected it up to the composite input on my TV.

Sadly, all is not well. The screen is full of characters that keep changing. When I hold the reset buttons, the screen is filled with a single character. When I release, its back to the random characters.

Does anyone have any suggestions?

All help gratefully received.

Dave

jltursan
November 19th, 2014, 11:10 PM
I'm not familiarized with the common faults a UK101/Superboard can suffer; but the usual culprit is the RAM. I suposse that at least the +5V supply to feed the 2114 RAMs is present; so my first suggestion is swapping RAM positions (if they're socketed, of course) and look for changes.

And btw, welcome to the forum! :)

wolfman_55
November 20th, 2014, 11:09 AM
Many thanks for the suggestion. This weekend i'll take all the RAM out but a couple of chips and see what happens. Luckily all the chips are socketed so if that doesn't work, I'll try removing some of the others that aren't really needed to get it going.

Just for info as well, I've got 3 Commodore Pets as well. One works, one doesn't and I've not tried the third yet as I want to clean it up a bit first.

Many thanks

Dave

daver2
November 21st, 2014, 12:51 PM
Hi Dave - welcome to the forum.

RS, UK101 and SoC MK14 - you must be based in the UK?

What test equipment do you have (if any)?

Do you have the schematics and are you able to read/understand them? See http://www.compukit.org/images/8/8e/Compukit-manual.pdf if you don't have them.

First thing would be to download the data sheets for all of the IC's and go around all the pins with a digital multimeter (dirt cheap ones can be picked up from Maplin if you haven't got one) to make sure you have +5V and 0V on each IC and it is within tolerance (+5V +/- 0.25V). Black lead (negative) to the 0V pin of the IC you are testing and the read lead (positive) to the Vcc pin of the IC you are testing. If this is OK everywhere - move on to stage 2.

Be careful though not to short out any pins of the IC's during this test process.

Clip the black multimeter lead (negative) on to the 0V of the power supply and attach the red lead to pin 40 (/RESET) of the 6502 CPU (IC 8). The voltage should be round about +5V (pulled to +5V via resistor R12 on page 17). The voltage on this pin should drop to nearly zero volts when the two RESET keys are pressed. The voltage should return to near +5V again when one (or both) reset keys are released. This tests out the RESET logic.

The next test(s) will depend upon how many of your ICs are socketed. If you could let me know I may be able to help you further.

It is good that you have something on the screen - this tells us that the bulk of the video circuitry and the clocks appear to be working (at least superficially).

Dave

wolfman_55
November 23rd, 2014, 01:32 AM
Hi DAve,

Many thanks for the info. Yes I am UK based.

I've jut purchased a multimeter with a frequency measurement facility, so I was going to try the various chip outputs to make sure they are at least changing, but I'll try your suggestions at the same time.

All the IC's are socketed, so I guess I could check each one individually on a breadboard, but that's probably a last resort as it sounds very time-consuming.

I'll let you know how I get on.

Dave

daver2
November 25th, 2014, 10:43 AM
Hi Dave,

I think you may be being optimistic regarding the frequency measurement capability of your multimeter - unless it is a good one.

I use a logic probe from Maplin (FY73Q at about GBP 15) - great Christmas present if you leave the code lying around the house! This unit can detect logic 0 and 1, open circuits and pulse trains. It also has a memory function.

The reason I was asking about the sockets was not to remove and test all of the chips but (a) they can be a source of problems and (b) it allows a simple way of temporarily 'bodging' bits of the internal logic for testing by removing the odd chip and installing some jumper wires.

One thing you may like to consider (after checking that the power supplies are OK on each chip) is to visually inspect the pins of the ICs. I had an Apple IIe disk controller card where two of the ICs had what looked to be dirty pins (a ROM and a bog standard SN74LS74). All the other IC pins were fairly dirt free. Upon using my IC extraction tool I found that some of the pins of the IC had been left behind in the IC sockets! The pins themselves had been 'eaten' through at the narrowest part and were effectively floating. A couple of replacement parts and all was well!

Look at the pins and see if they are dirty. If they are, remove the IC and clean the pins (I use a pencil eraser), and re-install the IC again. Don't forget to use either an antistatic mat or a piece of aluminium foil to prevent damaging the semiconductors with electrostatic discharge.

The pins of the IC socket can also become dirty. Removing and reinstalling the ICs will help break any film that has built up. A small squirt of contact cleaner (the type that doesn't leave a residue) may also help.

The next thing would be to chase the logic through.

You will already have checked the power supply to the ICs and the reset signal. Next will be to see if we have a clock. IC58 pin 3 should have an 8 MHz square wave on it (this will be the highest frequency you will need to measure with your multimeter). IC29 pin 11 should have a 1 MHz square wave on it. This is the CPU clock to pin 37 of IC8 (6502).

Have a go at the above and I will print the schematic out and see if we can identify the easiest way of identifying the culprit ICs.

Dave

wolfman_55
December 5th, 2014, 03:45 AM
Hi Dave,

I'll have a go over the weekend. I did take all the RAM out, and that made no difference.

I've also order a TTL IC tester from China, but that will take weeks to arrive, so I'll get stuck in as you recommend.

http://www.ebay.co.uk/itm/271634652740?_trksid=p2059210.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Dave

daver2
December 8th, 2014, 10:10 AM
Dave,

Because your access to test equipment appears limited - what I am thinking about is to remove the 6502 CPU and replace it with a small test box (consisting primarily of switches and LEDs) to 'fake' the read and write states of the CPU. You will have to build this test box yourself from Maplin parts - although you could 'breadboard' it and re-use the components later as an I/O test box for your UK101 expansion port!

Use of the test box should permit you to read and write from/to the RAM devices, read from the ROM devices, and to play with the keyboard and VDU RAM to see if things respond correctly (i.e. you should be able to write known characters into the VDU RAM and see if the correct characters are displayed at the correct location on the screen). It will be a bit laborious to check out all of the data programmed into the ROMs - but a sample check with ROM images downloaded from the internet should suffice (I found a UK101 emulator on source forge containing the ROM images - although there is no guarantee that they are the same version as what you have). Checking the MONITOR ROM should also suffice to get a working UK101 (the BASIC interpreter is much larger than the MONITOR so will take much longer to check out).

If this sounds to be the sort of thing that would be useful to help you fault find - then I will be quite happy to sketch something out for you.

Dave

dfnr2
December 8th, 2014, 09:56 PM
Hi All,

Just joined in the hope of some help.

My first computer was a Science of Cambridge MK14, which sadly I don't have any more. My second was a UK101 which I'm now trying to get working. It was heavily based on the Ohio Superboard that was available at the time.

I've replaced three damaged keys (Many thanks RS who still stock them!), sorted out a better 5v PSU and connected it up to the composite input on my TV.

Sadly, all is not well. The screen is full of characters that keep changing. When I hold the reset buttons, the screen is filled with a single character. When I release, its back to the random characters.

Does anyone have any suggestions?

All help gratefully received.

Dave

Hi Dave,

A short video would help. It sounds like the whole screen fills with legal characters, which means a large part of the video circuit is working. When you say the screen fills with random characters, are they random, or the same each time? It's strange that the screen fills with a single type of character during reset. Nothing should be happening then. Is that the same character each time as well? Outside the video circuitry, there's not much more to the machine than a CPU, some RAM, and ROM. I've seen the 6502 go bad, and also the ROM/EPROM. You really want an oscilloscope, but you can do a lot with a DMM (for static measurements only), and a logic probe. Are you able to post a video, or at least a few pictures of the sequence of events?

There are lots of resources on http://osiweb.org, including links to debugging resources. Also, consider posting on the forum there.

Dave

tinplatepete
November 15th, 2015, 02:21 PM
Hi Dave.
I know this is an old thread, but I have just joined this forum. I am a fan of the UK101 and I was wondering if you sorted your UK101.
Pete

daver2
November 19th, 2015, 09:48 AM
Hi tinplatepete,

Welcome to the forum.

I am afraid Dave (aka wolfman_55) has never visited the forum again since his last post of December 2014. I guess he gave up?

Dave

tinplatepete
November 19th, 2015, 10:33 AM
Hello Daver2.
Thanks for that. That is a shame; I am just in the process of rebuilding a UK101 and trying to make contact with other members with the same interest. My UK101 was lost some time back It had all the premier Eprom upgrades, Sound, Colour,32K ram, and Floppy Drive. I recently acquired an untouched UK101 and I am in the process of trying to recreate at least a part of it my old machine and that’s how I came across this forum.
The only parts I have of my old UK101 is a few of the eproms and 32K Ram card.
I am fortunate enough to have an eprom burner and have added Cegmon, Basic 5, and Toolkit, by looking for the rom images on the net. I am still looking for Basic X but with no luck.
I may start a new thread to see if anyone can help.
Pete