Problem with H4 not booting (zChris's board)

[PhilC]

Afternoon All,

I wondered if you all could do me and @zChris a favour.

zChris now has one of my H4 boards which worked fine when it was with me and initially fine when it arrived with zChris. Unfortunately that's no longer the case.

I'm sure that if I had the board here with me, instead of in Sweden then it would have been diagnosed and fixed by now.

So I'm using this thread to help zChris get the H4 back up and running.

He does have a small logic analyser and a Rigol scope.

Please all feel free to chip in if you can think of anything that helps, as my remote diagnostic skills aren't as good as my in person ones.

[PhilC]

So the background is that all chips have been removed and reseated (except for the MMU and GLUE which are SMT, that is still the case right zChris?)

The board is confirmed as resetting by watching the /RESET and /HALT pins on the CPU but all that is present is a white 60hz screen, so its halting for some reason.

@zChris with your scope could you please try the following:

On the Shifter could you please check pin 2 for a 32mhz clock signal and pin 39 for a 16mhz clock signal.
Presuming you still don't have a blister, can you make sure that both glitter jumpers are still fitted.
Jumpers 3,6,7,8,9,11 & 12 have jumpers fitted but not JP10.

[exxos]

https://www.exxosforum.co.uk/forum/viewt ... =78&t=2362

https://www.exxosforum.co.uk/forum/viewt ... =78&t=2785

[rubber_jonnie]

So that sounds like maybe ROM problems to me, I got a white screen and the problem was the LS11 was not fitted, so assuming it is fitted you may want to have a look at the outputs from that and check the ROM is good elsewhere if possible.

[PhilC]

@rubber_jonnie I'd initially thought rom but had forgotten about the LS11 :-D

[zChris]

Alright i tried looking for how you do the measure and i think im on the right track. Doesnt seem that i get any signal, looks constant 5v.

DSC_1369.JPG

DSC_1368.JPG

[zChris]

Ive measured the legs on LS11 and did not find any shorts between them.

/zChris

[exxos]

You need to check this line to see if you get a pulse after reset..

Capture.JPG

Also check reset on CPU pin 20... but like I posted earlier read this... https://www.exxosforum.co.uk/forum/viewt ... 559#p68736

[zChris]

I have checked for shorts and pull ups. The only "weird" results was resistance between VCC and PIN 12 which was 1.5K, Pin 18 = 0.94k (ok?), Pin 26 = 1.09K.

Then i went to checking that leg on LS11. Should there be any connection between these points? THats how i interpreted the image @exxos posted.

2021-08-16_19-41.png

[exxos]

You need to check that line I highlighted.. but check it on the jumper on your scope and keep pressing reset to see if it changes.