A3000 power on test check error

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jpagen
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Re: A3000 power on test check error

Post by jpagen » Wed May 13, 2020 10:34 pm

Hi All

Seem to have gone back a step!

Got some new SN74LS145N today and inserted in to the sockets.Tried the RAM TEST ROMs which boot but there is no response from the keyboard.
Swapped in the RISCOS 3.11 ROMs and changed the ROM jumpers but they refuse to boot with no POST boot flashes or messages. :shock:

Checked my soldering on the sockets and continuity from each pin through to the back of the PCB which seems OK. I've got 4 x74LS145Ns (1 original and 3 new) so I have tried swapping them around but no change. I guess my next step will be to check continuity from each pin on the SN74LS145n's through to the keyboard connectors...a job for the weekend!

Anyone have any other suggestions?

Thanks as always!

jpagen
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Re: A3000 power on test check error

Post by jpagen » Thu May 14, 2020 10:43 pm

Hi All

Managed to get a bit of time after work today to check my connections from IC4 and IC5

According to the circuit diagram http://chrisacorns.computinghistory.org ... awings.zip, most of the connections on IC4 and IC5 appear OK. However there seems to be some issues. I believe I should have continuity on the following but I don't-
IC4
  • Pin 10 to LK 12 (I seem to have continuity to LK 9 instead :? )
  • Pin 12 to IC2 Pin 24
IC5
  • Pin 7 to LK9 (I seem to have continuity to LK10 instead)
  • Pin 10 to LK11 (not LK 12 which is what I have)
  • Pin 11 to LK10 (not LK 11 which I have)
All other connections appear to be OK.

Would appreciate someone with more expertise than I have confirming I have read this correct! I notice the circuit diagram references issue A motherboard in the bottom right of the diagram but mine is an Issue 3 if this explains any differences.

Thanks

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IanS
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Re: A3000 power on test check error

Post by IanS » Thu May 14, 2020 11:09 pm

jpagen wrote:
Thu May 14, 2020 10:43 pm
  • Pin 12 to IC2 Pin 24
I'd focus on this. Without that connection, none of the keyboard is likely to work correctly.

The other links (LK<x>) are not likely to be an issue, just looks like Acorn may have re-ordered them between revisions, or it just never matched the PCB. The links are all marked as NF (not fitted), so unlikely to be an issue.

jpagen
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Re: A3000 power on test check error

Post by jpagen » Fri May 15, 2020 10:39 pm

IanS wrote:
Thu May 14, 2020 11:09 pm
I'd focus on this. Without that connection, none of the keyboard is likely to work correctly.
Thanks IanS-you were right! I restored the Pin 12 to IC2 connection this evening, rechecked all the traces from IC4, ignoring the different LK<x> and the machine accepts keyboard input with the RAM Test Roms installed

However, when I swap the Riscos 3.11 or Riscos2 Roms back in(changing LK17-20 as needed), the screen flashes once and then goes blank screen (even when doing a Power on - Del CMOS reset). I have tried re-seating socketed ROMs in case anything had worked loose while replacing the IC4/5. There are no messages, noises or POST flashes with the RISCOS 3.11 ROMs. :? The keyboard power LED lights normally.

Any suggestions would be appreciated.

Thanks

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IanS
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Re: A3000 power on test check error

Post by IanS » Fri May 15, 2020 11:17 pm

Not sure what to suggest, if the test roms show a video display, then aiui risc os 2 should display something. I don't think swapping from test roms to risc os 2 should need any link changes. How confident are you in the risc os roms being all good? Can you post pictures of the roms fitted and the link settings?

At the risk of stating the obvious, for delete reset, you can't hold delete too early or for too long. press delete, power-on, wait for the desktop. You should see a red border on the screen if the delete reset worked.

jpagen
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Re: A3000 power on test check error

Post by jpagen » Sat May 16, 2020 5:51 pm

IanS wrote:
Fri May 15, 2020 11:17 pm
Not sure what to suggest, if the test roms show a video display, then aiui risc os 2 should display something. I don't think swapping from test roms to risc os 2 should need any link changes. How confident are you in the risc os roms being all good? Can you post pictures of the roms fitted and the link settings?

At the risk of stating the obvious, for delete reset, you can't hold delete too early or for too long. press delete, power-on, wait for the desktop. You should see a red border on the screen if the delete reset worked.
Thanks IanS for responding.

Just found the problem! :D

There was a break between IC5 pin 12 through to IC9 pin 8. Very odd it was exactly the same pin on IC4 that also needed a repair last night. Got RISCOS3.11 up and running. Not sure what IC9 is but I am guessing the bad connections were preventing the DEL key from doing a CMOS power on reset.

Still got the following issues
1) On board RAM faulty (can only boot with a 4 MB Ram module fitted). Got some TC514256AZ10S waiting to try
2) Keyboard LED's not working or very dim. Power LED is fine though. Looking at the circuit diagram the other LEDs all seem to have the IC3 in common, so I am guessing I should look at the traces to and from the IC3 first.

Thanks for the help

sP1d3r
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Re: A3000 power on test check error

Post by sP1d3r » Mon May 25, 2020 8:35 am

jpagen wrote:
Sat May 16, 2020 5:51 pm
IanS wrote:
Fri May 15, 2020 11:17 pm
Not sure what to suggest, if the test roms show a video display, then aiui risc os 2 should display something. I don't think swapping from test roms to risc os 2 should need any link changes. How confident are you in the risc os roms being all good? Can you post pictures of the roms fitted and the link settings?

At the risk of stating the obvious, for delete reset, you can't hold delete too early or for too long. press delete, power-on, wait for the desktop. You should see a red border on the screen if the delete reset worked.
Thanks IanS for responding.

Just found the problem! :D

There was a break between IC5 pin 12 through to IC9 pin 8. Very odd it was exactly the same pin on IC4 that also needed a repair last night. Got RISCOS3.11 up and running. Not sure what IC9 is but I am guessing the bad connections were preventing the DEL key from doing a CMOS power on reset.

Still got the following issues
1) On board RAM faulty (can only boot with a 4 MB Ram module fitted). Got some TC514256AZ10S waiting to try
2) Keyboard LED's not working or very dim. Power LED is fine though. Looking at the circuit diagram the other LEDs all seem to have the IC3 in common, so I am guessing I should look at the traces to and from the IC3 first.

Thanks for the help
You'd have to disassemble the keyboard, clean and lubricate the leds where they contact the keyboard membrane to make them brighter.
I've got some experience of disassembling keyboards, it's quite time consuming and you need to be careful with the plastic parts.
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jpagen
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Re: A3000 power on test check error

Post by jpagen » Mon May 25, 2020 10:36 pm

IanS wrote:
Tue Mar 24, 2020 10:49 pm
Looks like D16-D19 are being read incorrectly, That corresponds to IC24. Check the connections to all the pins and trace the data pins back to the ARM via R50,R115,R116,R117.
I finally replaced IC24 and issue resolved. No more corrupt display when booting with the on board RAM. :D
sP1d3r wrote:
Mon May 25, 2020 8:35 am
You'd have to disassemble the keyboard, clean and lubricate the leds where they contact the keyboard membrane to make them brighter.
I've got some experience of disassembling keyboards, it's quite time consuming and you need to be careful with the plastic parts.
Thanks! What did you use to clean the contact between the membrane and LEDs? I tried some IPA but didn't notice any improvement. The Caps Lock is very feint but cannot see any light from the num lock or scroll lock.

Apart from the keyboard LEDs everything seems good now :)

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Re: A3000 power on test check error

Post by steve3000 » Mon May 25, 2020 11:02 pm

jpagen wrote:
Mon May 25, 2020 10:36 pm
IanS wrote:
Tue Mar 24, 2020 10:49 pm
Looks like D16-D19 are being read incorrectly, That corresponds to IC24. Check the connections to all the pins and trace the data pins back to the ARM via R50,R115,R116,R117.
I finally replaced IC24 and issue resolved. No more corrupt display when booting with the on board RAM. :D
Excellent - glad to hear you've successfully restored your A3000 back to it's original early 90's greatness :)

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Re: A3000 power on test check error

Post by sP1d3r » Tue May 26, 2020 8:38 am

jpagen wrote:
Mon May 25, 2020 10:36 pm
Thanks! What did you use to clean the contact between the membrane and LEDs? I tried some IPA but didn't notice any improvement. The Caps Lock is very feint but cannot see any light from the num lock or scroll lock.

Apart from the keyboard LEDs everything seems good now :)
I used IPA to thoroughly clean the legs of the LED and then some WD40 on a cotton bud to lubricate the led and the contact pad, dab the pad carefully or you'll rub away the conductive layer. WD40 improves electrical contacts, e.g. spraying on ht leads and spark plugs to keep out moisture.
The green translucent plastic in the key might need cleaning also, I use tweezers to unclip the key from the guide.

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Re: A3000 power on test check error

Post by steve3000 » Tue May 26, 2020 9:23 am

sP1d3r wrote:
Tue May 26, 2020 8:38 am
I used IPA to thoroughly clean the legs of the LED and then some WD40 on a cotton bud to lubricate the led and the contact pad, dab the pad carefully or you'll rub away the conductive layer. WD40 improves electrical contacts, e.g. spraying on ht leads and spark plugs to keep out moisture.
:shock: I’d not put WD40 anywhere near the inside of my computers...

Agree it works nicely in cars, keeping out moisture from spark plugs - but this is because it coats the surface of spark plugs/ht leads/etc with a film of oil - and it removes carbon deposits by chemical action. Since the contact pads on the keyboard membrane are carbon, this seems to me like a very bad idea...

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Re: A3000 power on test check error

Post by sP1d3r » Tue May 26, 2020 11:44 am

steve3000 wrote:
Tue May 26, 2020 9:23 am
sP1d3r wrote:
Tue May 26, 2020 8:38 am
I used IPA to thoroughly clean the legs of the LED and then some WD40 on a cotton bud to lubricate the led and the contact pad, dab the pad carefully or you'll rub away the conductive layer. WD40 improves electrical contacts, e.g. spraying on ht leads and spark plugs to keep out moisture.
:shock: I’d not put WD40 anywhere near the inside of my computers...

Agree it works nicely in cars, keeping out moisture from spark plugs - but this is because it coats the surface of spark plugs/ht leads/etc with a film of oil - and it removes carbon deposits by chemical action. Since the contact pads on the keyboard membrane are carbon, this seems to me like a very bad idea...
:roll: I don't know if it would mix well with conductive paint and the like but I've not had any problems with WD40, I use it quite a lot in my computers for lubricating connectors and contacts. I use it on my keyboard membrane and connector to reduce friction which wears away the contact pads.

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Re: A3000 power on test check error

Post by sP1d3r » Tue May 26, 2020 2:03 pm

steve3000 wrote:
Tue May 26, 2020 9:23 am
:shock: I’d not put WD40 anywhere near the inside of my computers...

Agree it works nicely in cars, keeping out moisture from spark plugs - but this is because it coats the surface of spark plugs/ht leads/etc with a film of oil - and it removes carbon deposits by chemical action. Since the contact pads on the keyboard membrane are carbon, this seems to me like a very bad idea...
I think that I've been lucky with using WD40 on my keyboard membrane connector because it'd make using conductive paint on a keyboard membrane with damaged traces impossible.

The keyboard membrane connectors on my A3000 motherboard are great in comparison with the ones on my A3020 motherboard, which damaged the keyboard membrane traces on several of the pins despite using WD40 to reduce the friction because the sprung bits of metal exerted too much pressure on the membrane traces and were slightly twisted.

I was able to fix this by straightening the sprung contacts and reducing the spring pressure with a small screwdriver and the keyboard still works properly because I noticed in time and I'd used WD40, so only a little of the carbon was scraped away.

However, because this makes disassembling my A3020 problematic I was thinking of modifying the membrane connector using something like a 40-pin card-edge PCB, which has the same pitch as the keyboard membrane connector, and a clamping arrangement like on a Spectrum Plus keyboard membrane.
An A3020/3000 keyboard membrane with damaged traces clamped to a suitable bit of card edge PCB would still work because of the length of the traces, I'd have thought.
Then a 40-pin ide ribbon cable with crimped header pins could be used to connect to the motherboard if standard 2.54mm pitch headers were soldered into the motherboard connector sockets, I thought.

I hope that my post didn't influence anyone with worn traces on their keyboard membranes to try using WD40 because an alternative keyboard membrane connector arrangement is the only option if the keyboard doesn't work properly other than getting a new keyboard from CJE'S or a donor A3000, unfortunately. :cry:

jpagen
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Re: A3000 power on test check error

Post by jpagen » Tue May 26, 2020 10:20 pm

steve3000 wrote:
Mon May 25, 2020 11:02 pm
Excellent - glad to hear you've successfully restored your A3000 back to it's original early 90's greatness :)
Cheers steve3000! It is actually better than early 90s. I only had 2MB back then. Now I have a massive 4MB! :D . Got an external CMOS battery fitted now and bypassed the sound filters. Also fitted an IDE to SD card interface, unheard of in the early 90s. Strangely the RAM Test ROMS still seem to stop after the progress line gets to the end of the first line but not had any issues in regular usage with RISCOS3. The RAM Test ROMS were still effective in diagnosing the IC24 issue.
sP1d3r wrote:
Tue May 26, 2020 8:38 am
I used IPA to thoroughly clean the legs of the LED and then some WD40 on a cotton bud to lubricate the led and the contact pad, dab the pad carefully or you'll rub away the conductive layer.
Thanks sP1d3r! just had another go at cleaning the LED contacts. Used some electrical contact cleaner on the LED pins rather than WD40 as it was to hand and the Caps lock and Scroll lock are much better. Need to have another go at the Num Lock LED though.

The old monitor is still in storage due to limited office space so only using a TV over SCART. For some reason I can only get a picture on a TV downstairs. I just get a grey screen on the one in the office(tried with and without a jumper on LK25). The picture quality downstairs is very good though...just a pain having to move the A3000 around.

Nearly complete!

jpagen
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Re: A3000 power on test check error

Post by jpagen » Sun May 31, 2020 9:57 pm

Spent a few hours this weekend stripping down the keyboard and giving everything a good clean. ..no change.

I then noticed there was a slight curve in the keyboard metal back plate ..between the LEDs which were not working...too much of a coincidence!

I temporarily placed some tissue between the membrane and metal back plate where the Num lock and scroll lock keys are to ensure there was contact between the membrane and LEDS all are now working. :) So simple. Need to try and find a way to flatten the metal plate sometime.

Some of the LEDs are still quite feint though. The LEDs are fine. Checked them and they are bright when testing with a battery.

I checked resistance from the LED contacts to the keyboard connectors and some a have higher resistance than the others. I think this is likely the issue behind some LEDs being feint. I had to use conductive paint to repair the battery corrosion on the membrane connector.

The only thing I can think of is running wires from the LEDs direct to the keyboard connector. I tried running copper wire over new conductive paint before it dried but it would not stay in place.

I did a search but did not find any solution. Does anyone have any other ideas please?

Thanks!

jpagen
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Re: A3000 power on test check error

Post by jpagen » Wed Jun 03, 2020 9:56 pm

Hi All

An update on my A3000 restoration.

The last problem was feint keyboard LEDs. Checking the resistance of the carbon based paint I used to repair my keyboard ribbon led me to believe that that was behind my faint LEDs.

I read this article about using nickel paint viewtopic.php?t=16045 and decided to replace the carbon based paint with nickel paint which greatly improved the conductivity on the ribbon cable and I now have bright keyboard LEDS :D

Finally seem to have a fully operational A3000!

The trace repairs to the mouse socket and the IC4/IC5 could be neater and I am not sure if the nickel paint on the keyboard ribbon is robust but everything seems to work.

I did sacrifice my 2MB RAM expansion board (unnecessarily) when trying to repair the onboard RAM but I have a 4Mb expansion anyway. If anyone knows where I can get a single D424256V-70 ZIP20 to repair my 2 MB RAM board I would be interested. There is a 5 pack currently available on a well known auction site but I only need one.

Thanks everyone for the advice and support over the last 4 months.

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Re: A3000 power on test check error

Post by jpagen » Sat Jul 18, 2020 4:01 pm

Hi everyone!

Switched on the A3000 today to find a new keyboard issue.

The following keys don't seem to be working:-
all 4 cursor keys
Numeric keypad keys 0,1,2,3,4
NumLock key LED

I have checked
  • Keyboard connectors through to IC4 & IC5 and up to IC2 and IC9 (where applicable) but they seem OK
  • Numlock LED which is fine
My guess is it is probably a problem with the keyboard ribbon which slots in to SK7. This was damaged by the battery but 'repaired' with nickel paint. I have checked the tracks which go to the LEDs but they seem OK. Not sure if there is a way to check the tracks which go to the keys which I assume are pressure sensitive.

There are quite a few posts on this forum about keyboard issues
This thread viewtopic.php?f=16&t=6002&start=30#p64302which shows the membrane map caught my eye but I cannot see any pattern with the keys I am having problems with.

Does anyone have any suggestions please?

jpagen
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Re: A3000 power on test check error

Post by jpagen » Sat Jul 18, 2020 8:34 pm

Found the problem. It seems that there is less contact between the keys and the membrane in that part of the keyboard. Applying a little pressure to the back of the keyboard is enough to address the problem. Just need to figure out a way to make the fix permanent now.

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