Go key doesn’t work on MK14 - UK Vintage Radio Repair and Restoration Discussion Forum

Pepperm · 26th Mar 2022, 5:28 pm

Hi

I am restoring my old MK14 (very slowly) and have just come across a strange problem…

The Go button just doesn’t work, but all the others do. I have traced, successfully, the Go button connections to the 80L95 (IC11) and the 7445 (IC13) but pressing it just doesn’t work. I have a replica MK14 and the Go button works as expected on that.

The original MK14 has all of the original RAM and PROMs and the replica has (is it Martin’s) add on ROM/RAM board with the same monitor code in it (giving a 0000 00 on power up).

Does anyone have any suggestions as to where I could look for a solution next please?

Mark

TonyDuell · 26th Mar 2022, 6:10 pm

If it's giving 0000 00 (as opposed to ---- --) then it's the 'new monitor'

I seem to remember that the new monitor enables interrupts and that you have to pull the SA (Sense A) pin to a particular state to be able to run a user program. Alas I forget if it's 'pull high' (to +5V) or 'pull low' (to ground) but a bit of work with a test lead should solve that.

Pepperm · 26th Mar 2022, 7:42 pm

Good suggestion… thanks for that, you have stirred a memory so I’ll give it a go. I’ll just look at the SA line on my replica.

Mark1960 · 26th Mar 2022, 8:22 pm

I have it connected to ground at the edge connector on my original.

You might have removed the link wire on yours when you had the single step circuit connected.

Mark

Mark1960 · 26th Mar 2022, 8:27 pm

Maybe worth mentioning that you might also have linked the sense input to INTR on the INS8154. If you did then it should work when the INS8154 is fitted.

Take care not to have it linked to both INTR and ground, in case you forget when you fit the INS8154 later.

SiriusHardware · 27th Mar 2022, 8:57 am

Just to enlarge on this, the 'new' monitor with the '0000 00' prompt has built in support for the 'single step' feature but it also requires the addition of some extra hardware and a switch.

If you don't fit the 'single step' hardware, the firmware side of the single step feature is still active so Sense-A needs to be tied low to keep single-step turned off, to allow the machine to run programs normally.

Slothie · 31st Mar 2022, 5:23 am

Its possibly a good idea to use a 1k-2k resistor to pull it down. You will then be able to drive it and use it in an application but the GO key will still work..

26th Mar 2022, 5:28 pm	#1
Pepperm Diode Join Date: Aug 2018 Location: Market Drayton, Shropshire, UK. Posts: 9	Go key doesn’t work on MK14 Hi I am restoring my old MK14 (very slowly) and have just come across a strange problem… The Go button just doesn’t work, but all the others do. I have traced, successfully, the Go button connections to the 80L95 (IC11) and the 7445 (IC13) but pressing it just doesn’t work. I have a replica MK14 and the Go button works as expected on that. The original MK14 has all of the original RAM and PROMs and the replica has (is it Martin’s) add on ROM/RAM board with the same monitor code in it (giving a 0000 00 on power up). Does anyone have any suggestions as to where I could look for a solution next please? Mark

26th Mar 2022, 6:10 pm	#2
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,208	Re: Go key doesn’t work on MK14 If it's giving 0000 00 (as opposed to ---- --) then it's the 'new monitor' I seem to remember that the new monitor enables interrupts and that you have to pull the SA (Sense A) pin to a particular state to be able to run a user program. Alas I forget if it's 'pull high' (to +5V) or 'pull low' (to ground) but a bit of work with a test lead should solve that.

26th Mar 2022, 7:42 pm	#3
Pepperm Diode Join Date: Aug 2018 Location: Market Drayton, Shropshire, UK. Posts: 9	Re: Go key doesn’t work on MK14 Good suggestion… thanks for that, you have stirred a memory so I’ll give it a go. I’ll just look at the SA line on my replica.

26th Mar 2022, 8:22 pm	#4
Mark1960 Octode Join Date: Mar 2020 Location: Kitchener, Ontario, Canada Posts: 1,294	Re: Go key doesn’t work on MK14 I have it connected to ground at the edge connector on my original. You might have removed the link wire on yours when you had the single step circuit connected. Mark

26th Mar 2022, 8:27 pm	#5
Mark1960 Octode Join Date: Mar 2020 Location: Kitchener, Ontario, Canada Posts: 1,294	Re: Go key doesn’t work on MK14 Maybe worth mentioning that you might also have linked the sense input to INTR on the INS8154. If you did then it should work when the INS8154 is fitted. Take care not to have it linked to both INTR and ground, in case you forget when you fit the INS8154 later.

27th Mar 2022, 8:57 am	#6
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,553	Re: Go key doesn’t work on MK14 Just to enlarge on this, the 'new' monitor with the '0000 00' prompt has built in support for the 'single step' feature but it also requires the addition of some extra hardware and a switch. If you don't fit the 'single step' hardware, the firmware side of the single step feature is still active so Sense-A needs to be tied low to keep single-step turned off, to allow the machine to run programs normally.

31st Mar 2022, 5:23 am	#7
Slothie Octode Join Date: Apr 2018 Location: Newbury, Berkshire, UK. Posts: 1,287	Re: Go key doesn’t work on MK14 Its possibly a good idea to use a 1k-2k resistor to pull it down. You will then be able to drive it and use it in an application but the GO key will still work..