Piggyback 4164 to Diagnose Memory Fault

[Chris_68]

Here are the ICs I mentioned: viewtopic.php?t=4557&sid=b7cb256a363fbe ... 031a4cfff4
Try to get A minerva or if you enjoy soldering just replace IC19-21, advice you to sacrifice them by cutting the pins and de solder one by one. You can always replace IC by IC.

[t0nyt]

Yes, RGB Scart connection on this

Funny thing is when reading the QL service manual it mentions the tweed moving down the screen and I wondered what it was on about as my working machine goes straight to tweed (to my eyes at least)

[Chris_68]

Hi,

I had multiple problems, a loose cable inside the DIN connector gave random green screen, then faulty logics gave different errors every time I booted, looked similar to what you posted. They are not expensive to order the ICs mentioned just in case, get 74HC instead of LS.

/Chris

[t0nyt]

Minerva ROM and the chips (in case needed) are ordered

Will report back when I have something to report!

Many thanks

[Popopo]

I had multiple problems, a loose cable inside the DIN connector gave random green screen, then faulty logics gave different errors every time I booted, looked similar to what you posted. They are not expensive to order the ICs mentioned just in case, get 74HC instead of LS.

Hi,
I think... HC is a different technology with different signal levels.
Did you mean HCT?
HCT keeps same levels than LS.

[t0nyt]

I had multiple problems, a loose cable inside the DIN connector gave random green screen, then faulty logics gave different errors every time I booted, looked similar to what you posted. They are not expensive to order the ICs mentioned just in case, get 74HC instead of LS.

Hi,
I think... HC is a different technology with different signal levels.
Did you mean HCT?
HCT keeps same levels than LS.

I actually ordered LS as I couldn’t find HC for sale

[Popopo]

I actually ordered LS as I couldn’t find HC for sale

Good
If 'm not wrong. LS, HCT and F types keep same signal levels.
F is easier to find than HCT (sometimes) and it is faster, what in general, should not be a problem.
LS is the most used in QL boards, at least what I see in mine and what Service Manual recommend.

[Peter]

F is easier to find than HCT (sometimes) and it is faster, what in general, should not be a problem.

This is a common but wrong belief. The 74F series has not just shorter propagation delay than 74LS, but also much faster signal rise/fall times, for which the QL mainboard was not designed. On a PCB which does not have adequate high frequency characteristics, higher rise/fall times lead to lots of ringing and crosstalk. Signal integrity could become a matter of luck.

[t0nyt]

One thing I've noticed is that as soon as the power is applied to the QL then MDV2 spins up for a couple of seconds

This is as soon as power is supplied (as I never get to the option to press F1/F2 for the normal MDV1 spin up)

[Popopo]

This is a common but wrong belief. The 74F series has not just shorter propagation delay than 74LS, but also much faster signal rise/fall times, for which the QL mainboard was not designed. On a PCB which does not have adequate high frequency characteristics, higher rise/fall times lead to lots of ringing and crosstalk. Signal integrity could become a matter of luck.

You are completely right.
Is the QL case?

In C. Amiga 500 it is not a problem. In some few more are neither a problem. But you are right, could be a problem because has not same features.