Woodstock IC voltages-- Tony? Anyone?



#17

Sorry to ask again, but I do want to fix my 29C. It turns on briefly, then shuts off as if being shorted out or the battery dying.

What pins should I check on the IC's to see if this is a power problem or a blown memory chip problem? Does the 29C have the same pinouts and votages as the other Woodstocks?

Thank you for helping me to try to revive this baby. It breaks my heart to see it sitting there, looking so awesome, but not working.

Michael


#18

I don't know if it is related to you problem, but have you read this article?

http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/articles.cgi?read=267

It somehow excludes the HP-29C, stating that it has different problems, but maybe it helps?

#19

The only similar unit is the 25C which uses (usually) only one of the same rams as the 29C. Other than that one ram IC, the other logic parts are different although the display parts are the same.

If you get a display of any kind, chances are very good the power supply is fine. The 0.00 display says the ACT is probably okay as well so I'd be focused on a rom or ram problem.

If there is any corrosion at all on the board, you'll need to remove it. Depending upon the severity, either remove the IC's and clean or soak the board standing on end in vinegar followed by a warm water wash and dry afterwards. The roms are the three 8 pin dips units along the left side, the two 14 pins on the right are the rams. The 8 pin above the ACT is a power up reset IC.


#20

Thanks, Klaus and Randy. I've read all the articles I can find. The board on this unit is in pristine condition. It doesn't look like the photo on the museum: it has a piggy-backed power board, but it looks like it is supposed to have this.

I was hoping to narrow down which chip is bad before I start unsoldering....

Michael


#21

Quote:
it has a piggy-backed power board

Very interesting, I've never seen that in a 2x calculator. Do you have a picture you can post or email?


#22

I think he is mostly likely referring to the separate power supply model that this board has:


#23

Randy: Exactly. Thanks... I was going to have to send a photo to Katie and have her post it. I hadn't seen that on any other Woodstock that I can recall, but the circuit traces would indicate that this was by design and not a later repair. But that's what it looks like....


#24

BTW, Randy, thanks for your help. It's really appreciated. I'd have sent this off to you already, but it turns out that I had already used the parts from my non-functional 19C many years ago to try to revive a 29C board that Katie W. sent me. I still have it, but I'd hate to have you have to swap around a lot of questionable chips. That's why I was hoping there was a way to pin down the offending component with the symptoms....


#25

You should have some basic functionality without the 0377 and 0379 parts installed.

If it sort-a-kind-a-works without those two, that is more than you had before removing them, I would take a guess and say it is the ram/rom IC marked 0379 as I've seen more of those fail than the others. If not, remove the two ram IC's and test again.

Just to repeat what you already know is that without known good parts to swap in, it is going to be very difficult to diagnose and repair :(

#26

Is this common to most 29C's, I don't have that in mine. The power supply is integrated into the rest of the main board like the other Woodstocks.


Edited: 3 Nov 2008, 8:39 p.m.


#27

Yes, I've found more 29C units with the PS module than those without. I think it was only the very early production units that had the parts on the board similar to the other woodstocks.

#28

not as an add on as in the first picture.

My HP21 exhibits a similar problem, however it was extremely corroded so no hope of resurrecting it.

Cheers, Geoff


#29

I removed the 0379 chip and then the calculator wouldn't even flash on. I then removed the 0377 and still nothing.

Does that point back to a power problem, or should I put both back and try to remove the memory chips?

Thanks! Michael


#30

Yes, re-install roms and remove the rams.


#31

Well, I re-installed the ROM's and removed the RAM's. No life at all anymore. I did notice that the ACT chip is a standard Woodstock chip rather than the gold/ceramic one's in the photos. Makes me wonder if it could be the source of the problems after all. SOOO frustrating. Thanks for all your help, though!!!

Michael


#32

Never mind. I see Katie's photo has the same type of ACT. Should the calculator turn on without the RAM chips installed?


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