A3000 restoration

salaxi54

Incoming ASROC!
AmiBayer
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Ok, some of you might have seen the board i got recently https://www.amibay.com/showthread.php?t=3079&page=126
It's a revision 9/03 mobo. First and notable defect is the U254 chip, an 74F646SPC Octal bus transceiver (by description). Although this is not a programmable IC, meaning it's of general use, i found quite a few variations of it. And not one of the various hires pics of an A3k mobo i found on the net had the exact chip. I've seen quite a few 74F646 ones, but not this particular one. So, without further ado, i'd like to know if i can use any one of the variations as an alternative.
Bought this mobo knowing that this chip was busted, so it has nothing to do with being cheated. ;)
Once i get this cleared and order the appropriate chip, i'll have to do something with the lack of a psu. Awaiting a big delivery of power supply 15-pin sockets, due to the fact that there was a minimum order limit. :(
Also got me a rather nice condition A3000 case waiting to be populated :)

EDIT: Here's the 'chipped' chip :D

CHIP1.jpg
 
Exactly! "Important Notice: Fairchild products cannot be sold or shipped outside of the Americas." LOL
Thanks for the link anyway mate! What i want to know is if the alternative 74F646's are compatible, and why the heck i haven't seen another A3000 with one like mine... :unsure:
 
Here is mine!



I'm trying to see if I can get you the chip.
 
Exactly! "Important Notice: Fairchild products cannot be sold or shipped outside of the Americas."

I daresay one of our fellow members on the other side of the pond might be willing to aid you here, if you genuinely can't get the part in Europe.

Once i get this cleared and order the appropriate chip, i'll have to do something with the lack of a psu. Awaiting a big delivery of power supply 15-pin sockets, due to the fact that there was a minimum order limit. :(

Nathan (AmigaManiac) sells ATX-to-A3000 PSU adapters, might be worth just getting one from him?
 
Did you see this link it's for fairchild in Greece..

http://www.fairchildsemi.com/cf/sc_Europe.html#Greece
:coffee:

Yup! Nadda! Lookie:

a) Available Quantity 0

74F6461.jpg


b) (translation) Attention! No relative components found

74F6462.jpg


c) No results found

74F6463.jpg


Andy, it don't have to be the exact chip if someone can verify the alternatives work.. I've sourced variations abroad that i can order. I know we have some wonderful people within the premises that would help indeed if need be (y)
As about Nathan's adapters i'm trully aware, but last time i had something come from down under it almost took between holidays :)
 
My friend, all mentioned parts are fully compatible with each other and will work.

On TTL world, what counts is the middle letters, not the suffix. So a 74F part can only be replaced by another 74F (or 54F, to complicate things a little, lol).

Explaining better: 74 is the prefix of ALL TTL chips, but those made to military specifications (insert MILspec jokes here), which then receive the 54 prefix. Nothing much different, only military parts can work in a wider temperature range and have ceramic bodies.

Then the "families":

74xx (where xx are numbers): first of all TTL chips, they are common as mud.

S (Schottky), one of the elder series, it is faster than normal 74xx chips, but tend to consume too much power;

LS (Low-power Schottky): tried to "cure" the S faults, but besides the low consumption, they are only a bit faster than ordinary 74xx chips.

F (FAST!): as name hints, those are only used when switching speed is really needed because its (for the era) high price.

HC/HCT: those in fact are ordinary CMOS chips with TTL pinouts for drop-in replacement with the advantage of very low power consumption. HCT is the attempt to reach higher speed operation. Both are the current "equivalents" are pure crap in my opinion. Avoid like the plague for anything more than drive a LED.
 
Thanks for the details Rogerio! What i've found abroad is an 74F646N. I guess that'll do the job :)
 
Yes, pretty much any 74F646 will do. 54F646 will do, also, but I think Doomy take all of those for his A2000 machines.
 
Yes, pretty much any 74F646 will do. 54F646 will do, also, but I think Doomy take all of those for his A2000 machines.

Lol, i knew Doomy had a high level of quality criteria, but i didn't know it was a Mil-spec level... :LOL:
 
These just came in today:

SOCKET3.jpg


SOCKET2.jpg


Brand new psu sockets! More than enough, so i guess i'll release them to the public soon. By the way, i located an 74HC646 locally, but Rogerio advised to stay clear of the HC kind.. Looks like i'll be ordering from abroad after all. :)
 
Mate - Shove the HC chip into a socket on the mainboard & if you get any troubles then I'm sure I can find & send one to you from the UK

(PS have you tried Futurlec ;))

Regards
TC :cool:
 
Thanks for the offer TC, i'll keep that in mind! (y) Tomorrow's the day. I'll do just that; get me a socket and try the HC chippy lol
Meanwhile, here's another part of the puzzle :

CASE2.jpg


CASE3.jpg


So, the pieces are coming slowly :)
 
It reminds me my Towerization operation: A3000D to A3000T, with Micronik A3000 (6910).

Good luck with this puzzle (y)
 
Nice A3000 project, looking foward many more pictures :D


@rkauer
thanks for the refresher on 74xx chips rkauer (y), you would`t have linky to any pics of the TTL 74xx series of chips would you, the ones I find never live up to my expectations

something like
http://138.37.35.209/staffinfo/davew/lab/74_chips/7404.gif

but for most of the series and that will fit one or 2 bits of paper. sorry salaxi back to you now... ribbits
 
Nope, never needed. When I'm in doubt I search for the datasheets.
 
Got this stuff today. Might as well go ahead and experiment with it.

74F6464.jpg


Couldn't find a 24-pin socket, so i got two 22-pin ones to custom-make one.. Things can only get better :)
Will also experiment with a spare power socket and see if i can cut hand-made protective caps for the cables, due to lack of availability on the market. (y)
 
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