Post Reply 
Found these inside a non-working 71B
03-10-2018, 11:18 PM (This post was last modified: 03-11-2018 02:27 AM by MikeSD.)
Post: #12
RE: Found these inside a non-working 71B
(03-10-2018 05:41 PM)AndiGer Wrote:  Wire near the right most pin seems to have no connection as well ...

I opened it up today to take a better look and get pics before I get going. I found other wires loose. I made voltage checks and found 5v on all the chips. I documented the connections for Din/Dout and all was ok.

Then I moved the FORTH (or whatever that chip is) And just like domino's a few more wires snapped.

I also noticed one of the ROMS looked like someone had lifted it a bit. When I touched it, there was a sound of speaker clicking, as if the it had life, albeit random running. I unpowered it and found the top ROM was loose from the bottom. At least there seemed to be wiggle between them. Worrisome because there are a lot of connections between them. Will know more when I remove board tomorrow.

So my plan for tomorrow is:

1) Remove the lower board and disconnect both the large RAM and the FORTH module
2) reflow the solder on all internal ROM chips, on lower board
3) inspect all connections for corrosion.
4) Then, before reinstalling RAM and FORTH, see if I can get 71B working first. I have other lower half if needed, but I think this one will be ok.
5) Then, if the 71B is working, reinstall the RAM first, since it was first in daisy chain after ROM and see how itvworks.
6) If all is good a t this point, reinstall the FORTH between RAM and HPIL, like it was before.

Should be a fun day Wink

Note: I haven't bothered to verify if the RAM is two 32K Ram for 64K total. Seems likely but I recall that the 64K had a battery for backup. We're all 64K two 32K devices or was there a 64k single devive.

Also, it appears these two might be wired as 2 seperate modules. I buzzed the Dout from the ROM to Din on the RAM but couldn't get continuity from the front RAM. And the top RAM Dout to the FORTH Din. So it looks like back RAM is daisy chained with front RAM. Makes sense. Looks like ROM9->RAMA8->RAMA9->RAMB8->RAMB9->FORTH8->FORTH9->HPIL (assuming pin 8 is Din and 9 is Dout. Wink

Think I have the daisy chain order wrong. Think the HPIL COMES before FORTH. Need to drag out the specs I guess. And I may have my pin numbers wring order but 8th and 9 are counting from left to right.

The RAM and FORTH are daisy chained between what I'm calling ROM (you can see red wire on chip on right) and that goes to large RAM on left, then to FORTH, then to HPIL. Can't put my finger on it but something seems odd. I would expect the 32k RAMs and FORTH to be at the end of a chain. But connecting to ROM chip and HPIL looks like it's in the middle. I know that's how it's connected. Better buzz this out once more.

[Image: 6x.jpg]
Find all posts by this user
Quote this message in a reply
Post Reply 


Messages In This Thread
RE: Found these inside a non-working 71B - MikeSD - 03-10-2018 11:18 PM
What's U10? - Dave Frederickson - 03-15-2018, 03:43 PM



User(s) browsing this thread: 3 Guest(s)