A2000 CPU pin 54

[giZmo350]

Could someone please verify if pin 54 of the A2000 CPU goes to pin 27 of U301 (CIA) and pin 27 U500 (ROM)? I know that pin 27 of U301 and U500 are tied together. The schematic is a bit confusing on bus D(0:15). Thanks much in advance!

[efrenmgp]

I think it goes to PIN 26 of U301 and pin 29 of U500. The pin you are following is D15 right?

(Checked here: http://www.amigawiki.de/doku.php?id=en:service:schematics)

Regards,

[giZmo350]

Thanks for checking efrenmpg... Yes, I noticed that it could also be interpreted that way. But notice, for example, at U500 all the bus identifiers have been shifted down one line on bus D15? Same thing at U301. If you look at the shifted number, they both point to pin 27. That's confusing to me.

Also, if pin 54 goes to U500 pin 29 & U301 PIN 26, shouldn't I have continuity between U500 pin 29 & U301 PIN 26? Which I do not. However, I do have continuity between U500 pin 27 & U301 pin 27.

See what I mean?

No continuity from CPU pin 54 to anywhere on U301 or U500 'cause I horked something replacing a corroded CPU socket.

Everything worked (intermittently) before I replaced socket and if I drop in an accelerator, I get a kickstart screen due to the on-board CPU being bypassed.

[efrenmgp]

I see what you mean... yes the schematics are confusing. The A500 schematic shows exactly the same thing.

OK I just double checked (and carefully counted pins)

I have an A500 6A motherboard here which I know is working. I assume that as far as D(0:15) goes it is the same as the A2000.

I *do* have continuity between CPU Pin 54 <-> ROM Pin 29 <-> CIA Pin 26
I *do not* have continuity between ROM Pin 27 and CIA Pin 27

Hope that helps

Regards,
Efrén

P.S. Later tonight I can check more things if you need. Let me know.

[giZmo350]

I see what you mean... yes the schematics are confusing. The A500 schematic shows exactly the same thing.

OK I just double checked (and carefully counted pins)

Thanks so much for your time Efrén!

I have an A500 6A motherboard here which I know is working. I assume that as far as D(0:15) goes it is the same as the A2000.

Yes, should be identical I would think.

I *do* have continuity between CPU Pin 54 <-> ROM Pin 29 <-> CIA Pin 26

OK, I have no continuity from CPU to either of those pins - but I probably wouldn't if the two meet back at pin 54 on the CPU and that's what I horked.

**But you DO NOT have continuity between ROM Pin 29 <-> CIA Pin 26?**

I *do not* have continuity between ROM Pin 27 and CIA Pin 27

OK, that's is concerning to me as I do have continuity between ROM Pin 27 and CIA Pin 27. I'm not sure what to think there. I'll have to go back to my board and poke around some more.

Hope that helps

Greatly! As at least I know how to correctly read the schematic and where pin 54 goes! Thanks so much!

Regards,
Efrén

[giZmo350]

Just rechecked board and I *do* have continuity between ROM Pin 29 <-> CIA Pin 26. So that's good!

I rechecked the soldering of CPU pin 54 under a magnifier and light and found that I lost half of the connection ring when desoldering and when I soldered the connection, coincidence would have it that,  I only got solder on the pin and non on what was left of the connection ring. And I use flux too! And I rechecked my solder joints like 3 times! And the solder joint looked OK! LOL Anyhoo, re-soldered the connection and it boots!

Thanks again Efrén! Without your verification I would still be guessing!

NEVER GIVE UP - NEVER SURRENDER! :laugh1:

[efrenmgp]

Hey! Good to know! I'm just glad it is working again