Via:      UK.AC.ULST.MGVAX; 12 NOV 92  9:31:29 GMT
Newsgroups: bit.listserv.i-amiga
Date:         Thu, 12 Nov 1992 09:29:00 GMT
From:         TJNT87@MGVAX.ULSTER.AC.UK

about two weeks ago I posted a problem I had with a VIRGO 2000 ram board!
I have already posted this but got no reply's so here it is again.

>Help! Help!

>Is there anybody in the UK or Europe that has a VIRGO2000 ram board (A500)?

>I have a problem using the extra 512K block of CHIP RAM in my VIRGO 2000 ram
>board.
>If I use more than 512K of chip ram(by loading programs on top of each other)
>the Amiga locks up(just as if it had run out of CHIP RAM?) so obviously the
>upper 512K block is not being used properly.

>The extra 512K block comes from block 4 of my VIRGO 2000 Ram board. I also have
>1.5Meg Fast ram from this trap door card and 2Meg from my Supra drive.
>I have tried every combination of RAM, startup-sequences and taking
>the Hard drive out, but to no avail.

>The extra 512K chip ram is addressed from 80000H to 100000H.

>My chip ram and fast ram check out OK using the RAMTEST function of my
>Action replay 3 so does that rule out the possibility of chip failure?

Ramtest function not much good!

>It's not the P.S.U. because I swapped my ordinary Amiga one for an PC AT one.

>The ram board has two meg in total and through the use of gary
>adaptor, pal chip and a two 74XX ic's as well as a wire soldered to
>JP7 (REV 6A board) I get the extra 1/2M chip and extra 1.5Meg FAST.

>I have since found out that VIRGO have gone bust so I cannot send the
>PAL back to see if it is faulty.

>I have since taken the board out, soldered sockets and socketed 44256
>100nsec rams onto main board - JP7 upper pads soldered to enable extra
>512k on board as chip. NOTE : THIS DOES AWAY WITH TRAPDOOR EXPANSION
>SO NO FAST. I have now got 1MEG CHIP 0 MEG FAST and 2MEG EXPANSION
>FROM SUPRA DRIVE AT SIDE.

>SO EITHER THE virgo board OR THE gary IC are at fault. I hope it's the
>GARY cos I will not be able to get parts for VIRGO BOARD.

WELL I found the problem:
	Something happened when I soldered new sockets into the board.

	The Virgo board uses a 2-4 line de-mux(74ls139) to select 1 of 4
	blocks of memory (1 block = 512K).

	At one of the sockets two of the select lines were shorted together.
Needless to say one select line went to the upper 512KCHIP block and the other
went to one of the FAST ram blocks. So when the uP accessed the upper 512K
chip block it was getting memory contentions from the FAST ram block as well.

I desoldered the socket in question and had a good close look at both socket
and board. The select lines did indeed free themselves from each other!
Could I find where the two lines had shorted? NO, I couldn't. I resoldered the
socket-AGHHHH SHORTS BETWEEN LINES AGAIN! Another very close look at the socket
and board-NOPE, doesn't look like any solder bridges. Desoldered the socket
again. Took the RAM CHIP AND soldered it in DIRECT with no socket. Yippee, says
I, when the multimeter didn't complain.

So now the board is back in circuit and working FFIIIINNNNNEEEEE.
What happened the socket? I just don't know.

It's not so hard figuring out now how the RAM is addressed. A PAL is used to
address decode and depending on the address, one of the four blocks of ram is
selected, amazing what you learn, ain't it!
Comments: Gated by NETNEWS@AUVM.AMERICAN.EDU