kodak80 H4 build (x2)

[PhilC]

Still scary turning on the power though.

Oh this should be a breeze compared to the Alpha, lol. Myself Icky and exxos had a fight on our hands at first just to get it to boot.

[Icky]

@kodak80 - I have found with the ALPHA and working my way slowly round the H4 most problems are solder related. Either a short, bad joint or missing solder.

I use this simple initial guide that I learnt from @exxos a long while ago when testing boards be it an ALHPA, H4 or plugin board like Flashy Clock. I actually do the short test before turning any board on now

• Check round all the CPU pins for shorts. This should be easy on the H4 as you can use one of the expansion sockets. I normally use a multimeter in continuity mode and usually start on pin 1 and pin 2 and then move the probes to pin 2 and pin 3 until I have walked around the whole 68K. Nothing should be shorting. I normally see between 500 to 1800 on my multimeter in continuity mode but if you have a 0 then there is something shorting.
• Check the pull-ups. Again walk around all the CPU pins and VCC (Pin 14 on the expansion socket) for pull-ups. All the address and data bus pins should be 2K2 others are1K as per the schematic. CLK and E are not connected to any pull-ups so shouldn't register any resistance.

I use the pinout diagram here https://www.exxosforum.co.uk/forum/viewt ... f=31&t=149 of the 68000 to aid running round the CPU pins.

[kodak80]

I have run round the pins on the GLUE, MMU, 27C4096 PLCC and an expansion socket and found no shorts.

I have tested 5v on all IC chips and these are good. Had to check continuity on the chips that sit under the power supply but this was also fine so assume 5v to these chips is good.

Tested resistance on the 68000 expansion socket:

2.2k: 1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 50, 51, 52, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64
1k: 10, 13, 17, 18, 19, 21, 22, 23, 24, 25, 26
1.5k: 12
VCC: 14,49
6.1k: 15
GND: 16, 53
7.6k: 20

Pin 15 is CLK and I have 6.1k resistance?
Pin 20 is E and has 7.6k?

Edited: after re-testing against VCC

[exxos]

75.4k: 14,49
6.1k: 15
GND: 16, 53
7.6k: 20

Pin 15 is CLK and I have 6.1k resistance?
Pin 20 is E and has 7.6k?

CLK & E don't have pull ups...

pin 14&49 is VCC, so why you got 75K on there ?

[derkom]

75.4k: 14,49

I think you tested these to GND, not to VCC. What about the rest then? All of these are pull ups, not pull downs. You need to be testing resistance to VCC.

[kodak80]

75.4k: 14,49

I think you tested these to GND, not to VCC. What about the rest then? All of these are pullups, not pulldowns. You need to be testing resistance to VCC.

Thanks. You are correct, these were all tested to GND. When I test these to VCC the resistance shows as a 0.3 which on my multimeter is a short so all good. Still learning how to fault find electronics as well as learning the functionality of all these chips.

[derkom]

Still learning how to fault find electronics as well as learning the functionality of all these chips.

Don't get the wrong impression that I actually know what I'm doing. But we are all getting better at this I'm sure.

Be sure to go back and test all the others to VCC as well.

[PhilC]

You certainly learn a lot by building and family finding these boards. It was difficult but fun to get the Alphas up and running at first.

Keep it up guys.

[kodak80]

Will re-check the expansion port resistance to VCC later as have to go to my day job now.

[kodak80]

I re-checked the resistance against VCC and have updated the readings above. Nothing really changed apart from the VCC pins. All other readings were similar.