exxos's Atari, Amiga & retro forum

Am I seeing the ROM in the wrong way round?

derkom wrote: 27 Apr 2020 14:50 I will admit I never actually knew what the DS1315 was for. :)

RTC :)

derkom wrote: 27 Apr 2020 14:50 I'll take another stab at it: You've got your TOS ROM 180° wrong. :mrgreen:

yep! Amazingly it fits in more naturally the wrong way around in those sockets, I think those came from rapid electronics :roll:

derkom wrote: 27 Apr 2020 14:50 Tell us how you feel about PLCC packaging.

:cussing: :cussing: :cussing: :cussing: :cussing: :headbang: :headbang: :cussing: :cussing: :cussing: :fire: :fire: :fire: :mad:

You love PLCC sockets really :)

:girldance: :girldance: :girldance:

:WTF: :WTF: :WTF:

I honestly don't believe what just happened... A booster was just doing tests... Then the power light started flashing on the keyboard... Something we shorting it out! I removed all the socketed chips and it was still the same...

So I took my low resistance meter and started measuring various points around the board, and the lowest resistance I found was around the capacitor on the right side of the H4...

So I removed it and tested it and found it was 1.54 ohms! I can't honestly believe a ceramic has failed in this way especially just out of the blue like this.


I suppose it is good testament that the soft start and current limit feature of my power supplies kicked in when it was needed!

Ceramic capacitors like to fail short circuited (or nearly short circuited). Particularly if they were mechanically stressed sometime before, either during manufacturing or (more likely) during assembly or use of the PCB.

I've heard of them cracking on PCBs due to various issues, but this one just seems to simply failed.


Some images... all looks fine other than one side, 3 and 3A (IPA cleaned) images.. its the only point it looks iffy.

The nasty thing is: You can often not see the crack damage. Don't think of it as the capacitor being broken in half. It's really subtle.

E.g. I learned not to place (in particular physically large) SMD caps near connectors on the PCB or near IC sockets. When you plug in the connector or push the IC into the socket, the PCB is inevitably flexed, leading to a latent capacitor damage that can become a reliability issue later. When ceramic caps fail, they usually fail with low resistance and not open.

I think the good thing which has come out of all this, is again, I think for the third time now, on how quick I have been able to diagnose faults on these H4 boards.

On original machines, I could spend all day trying to figure out what broke, in the end I just end up giving up and getting a fresh board to work with. Problem being in that case, I would generally have to start with changing the ROM & CPU (IE socket them) And then have to do various mods and fixes to get it back to a stable state.. Only to find within a week later that board has died and around in circles I go again :roll:

Having multiple CPU sockets makes life so much easier testing out upgrades as well. Even if a socket broke, I don't have to spend time messing about changing that socket or looking for new ones etc I can just simply plug into a different socket and fix it another time.

I think it is official that the H4's are just the future now. When I get more time and i'm going to start sorting out all my motherboards and just keep a small selection of different ones, and either sell or strip the rest for spares as they are just not worth bothering with anymore.

Totally agree @exxos the H4 is so much easier to work on, so much so I too have started to ditch the original motherboards and am only using the H4 platform for testing. As you say having 4x expansion slots and all the jumpers to tap into makes this so much easier.

Got fedup of my PSU being "unstable" as in squashing pins, being balanced on bags to lift it up.. so decided to do something about it all...


My immediate thought was to use 6 inch nails, but unfortunately I can only find three :cry:


So I find some bolts and lock nuts and did this...


And isn't that just typical! :roll:


So out came the drill and now I have a more permanent and proper fixture for my power supply :D