UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - MK14 programming interface

Timbucus · 24th Apr 2019, 9:14 pm

Sorry guys I have been offline as my PC went fut - just getting back under way!

Well now to prove that the chip is the cause of the typing issues for you I need to send it back as it seems to work fine for me and see if you still get the issue... but,

All my resistors are 1.2k so my pullups R7-R10 on the keypad rows are 1/4 the value of yours... that also means the pullups on D0-D3 are 1/6th of the size. R12-R15 (marked 11-15 on the revision II diagram) in the top corner on end. They give the xxxx1111 on the KB read I assume.

So by my view mine should transition faster - I will swap my pullups to 4K7 and put the suspect chip back in!

R7-R10 should not affect anything but may account for my funny resets at times as the D0-D3 will take longer (on yours) to get to transition and I wonder if that affects the strobing of the top 4 address lines? I will put them up to your 6K8 and see if that improves.

Obviously all this depends on the capacitance of different trace layouts as well and perhaps slightly different spec chips, especially on the D0-D3 side as a lot of chips touch the bus.

I may not have time until the weekend to try that now as still some work to do getting my PC fully operating like restoring the raid functions!

The VDU test will be useful as I have now had my PCB's from Martin so will be looking to build it and I just assumed I could substitute...

24th Apr 2019, 9:14 pm	#74
Timbucus Octode Join Date: Mar 2019 Location: Barry, Vale of Glamorgan, Wales, UK. Posts: 1,364	Re: MK14 programming interface - MK2 Sorry guys I have been offline as my PC went fut - just getting back under way! Well now to prove that the chip is the cause of the typing issues for you I need to send it back as it seems to work fine for me and see if you still get the issue... but, All my resistors are 1.2k so my pullups R7-R10 on the keypad rows are 1/4 the value of yours... that also means the pullups on D0-D3 are 1/6th of the size. R12-R15 (marked 11-15 on the revision II diagram) in the top corner on end. They give the xxxx1111 on the KB read I assume. So by my view mine should transition faster - I will swap my pullups to 4K7 and put the suspect chip back in! R7-R10 should not affect anything but may account for my funny resets at times as the D0-D3 will take longer (on yours) to get to transition and I wonder if that affects the strobing of the top 4 address lines? I will put them up to your 6K8 and see if that improves. Obviously all this depends on the capacitance of different trace layouts as well and perhaps slightly different spec chips, especially on the D0-D3 side as a lot of chips touch the bus. I may not have time until the weekend to try that now as still some work to do getting my PC fully operating like restoring the raid functions! The VDU test will be useful as I have now had my PCB's from Martin so will be looking to build it and I just assumed I could substitute...