Found these inside a non-working 71B

[MikeSD]

I was working on a couple of prospect HP-71B that might turn out ok, if I could repair them. One has very nice LCD and bezel and keyboard. But it is one of those that has the cable and they fracture easily.

When I opened it up, I found two modules already wired inside. And the bypassed cable was already bypassed but a few wires were disconnected.

At first I thought cool, RAM. But two chips didn't make sense, unless they were high density. Who would wire a couple of 4K RAMS? I thought 32K and/or 64K?

When I tried to identify them, I couldn't make a match. One part number vaguly looks like HP 5061 7234. The only thing that comes up for that is FORTH Assembler. Could that be a FORTH module? The last digit is hard to make out. Could be '0' or '9' but the loop looks too small for a '0'.

The other one looks different from a 4K.

Any idea what these might be?

Mike

These are the only 2 internally wired devices.

[Dave Frederickson]

The bottom pic shows what looks like a couple of CMT memory modules, just like the pic of the P01 internals on your website. The top one could be a ROM as you speculated.

EduCALC offered an internal module installation service back in the day.

Dave

[MikeSD]

(03-09-2018 08:31 PM)Dave Frederickson Wrote:  The bottom pic shows what looks like a couple of CMT memory modules, just like the pic of the P01 internals on your website. The top one could be a ROM as you speculated.

EduCALC offered an internal module installation service back in the day.

Dave

The fact that it's on the port 4 end seems significant as well.

I've got some better photos and the internal wiring. Hardly a schematic but might be a clue. I tediously replace the wirewrap bypass on the flex circuit that was removed. Some of those wires broke off. I used shorter wire that I have had success with before. Powered it up and right half of display lit up and a couple of cursors but no activity.

Then, I buzzed everything out and it was ok. Buzzed pin to adjacent pin. And end to end on the wires. All looked good there.

Then, I peaked under these devices to see if it was going to be able to check for broken wires. Sure enough there was another broken wire. However, I'm not sure where it goes. I have my suspicion. Need to drag out the tech manuals and see if I can figure out where it might go. There is a wire end still on the device, that looks like where it broke off, but I hesitate to hook it up without knowing.

I had done a triage on these once upon a time, and had this one marked "No Hope". I didn't even notice the internal wired components at that time. Glad I took a 2nd look.

Will post more photos later. And by more I mean better.

This is what was in the programmer. I think this is two 32K RAMS. Maybe that is a 32K RAM. That would be nice, even if I never get the 71B working. But I think I can, unless one of the HP chips are bad.

[MikeSD]

I have time to post one pic that shows the wire that broke on the RAM and where I think it goes. Seems so match up with the tail of a wire on the RAM.

[Paul Berger (Canada)]

starting from the left there should be wires from the board to the first 8 pins and then one to the far right. +5V is the far left followed by the four bus lines, then *str (strobe), C/D, and Din. The far right is GND. The connection you are pointing at would be B0.

Paul.

[rprosperi]

(03-09-2018 08:02 PM)MikeSD Wrote:  When I tried to identify them, I couldn't make a match. One part number vaguly looks like HP 5061 7234. The only thing that comes up for that is FORTH Assembler. Could that be a FORTH module? The last digit is hard to make out. Could be '0' or '9' but the loop looks too small for a '0'.

I suppose it could also be 5061 7238 which is the Surveying ROM (with only portions of the smaller upper loop visible), which might also make sense for a high-end machine with lots of RAM inside. The style of the '8' in the line below is different, but it almost looks like each character was stamped separately, so hard to tell.

You'll just have to fix it and turn it on I guess to be sure... ;-)

[SlideRule]

"… The last digit is hard to make out. Could be '0' or '9' but the loop looks too small for a '0'…"

Me thinks it resembles a 4!

SlideRule

[MikeSD]

(03-09-2018 11:12 PM)Paul Berger (Canada) Wrote:  starting from the left there should be wires from the board to the first 8 pins and then one to the far right. +5V is the far left followed by the four bus lines, then *str (strobe), C/D, and Din. The far right is GND. The connection you are pointing at would be B0.

Paul.

I need to get home and look at it again.the broken wire might go to the 4th from left. Something else noticed in the photo. Pin 9 on RAM board looks a lityle brown. And the far right pin looks to have a bubble of solder at 71 board. mihgt have had a short at one time

[Paul Berger (Canada)]

(03-10-2018 02:03 AM)MikeSD Wrote:  

(03-09-2018 11:12 PM)Paul Berger (Canada) Wrote:  starting from the left there should be wires from the board to the first 8 pins and then one to the far right. +5V is the far left followed by the four bus lines, then *str (strobe), C/D, and Din. The far right is GND. The connection you are pointing at would be B0.

Paul.

I need to get home and look at it again.the broken wire might go to the 4th from left. Something else noticed in the photo. Pin 9 on RAM board looks a lityle brown. And the far right pin looks to have a bubble of solder at 71 board. mihgt have had a short at one time

That looks like flux residue on pin 9 flux residue is usually not an issue. That blob of solder where the right pin (GND) connects to the board looks like bad soldering, could be a problem.

One of the modules should have a wire to pin 8 (Din) from the board and then pin 9 (Dout) of that module should connect to 8 of the next one and so on. This is the daisy chain that is used to configure the memory devices.

Paul.

[AndiGer]

Wire near the right most pin seems to have no connection as well ...

[Raymond Del Tondo]

Hi Mike,

a small side note: There are several areas of battery acid contamination. On the first pic near the PCB edge and the 6th connection from left, and in the 2nd pic in various places, even at and under the piggy-packed ICs.
So if the unit won't work after resoldering the other wires, this could be another area for cleaning;-)

[MikeSD]

(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

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.

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.

[Paul Berger (Canada)]

Pin 8 is Din and pin 9 is Dout you only need to look at the schematic to verify this. I received a non-working 71B that had two 32K modules inside much like yours. The way it was wired up they broke into chain 0 which is the chain that normally includes the four internal 4K RAM modules and the HPIL adapter. The chain starts off with the the Din pin of U6 (bottom module on right looking from the front) Dout from it goes to Din of U7 (Top right) Dout from U7 goes to U8 (Top Middle) Dout from U8 goes to Din of U9 (Left) and Dout of U9 goes to Din on the HPIL connector. The bottom middle is the OS ROM module and it does not matter because it is a hard configured module.

On the one I have have in front of me, they broke into the chain by disconnecting Dout on U7 (Top Right) from the board. Dout from U7 was routed to Din of the first 32K module Dout of 32K-1 went to Din of 32K-2, Dout from 32K-2 was then connected to the board connection where Dout from U7 used to be connected. Now the Chain is U6, U7. 32K-1, 32K-2, U8, U9, and HPIL.

The 71B I received with the extra RAM was really dead so I transferred the two 32K modules into another 71B. I also went a little further. You will note that there are pads behind the connector for U9 that looks like you could put another module on top, and you can, however to make it work you need to cut a trace on the under side of the board that connects Dout of U9 to the HPIL connector. The Dout of U9 is connected to Din of the pads for the top left as well and Dout of the top left is also by default connected Din of the HPIL connector, so cutting this one trace will disconnect Dout from U9 from Din on the HPIL. I know that this works because I have a third 32K module in this position. If you would like to do this let me know and I will take a picture of where the cut needs to be made.

Looking at the picture I see someone has added a module on the top left already.

On all of the modules pins 1-7 and 13 are all connected in parallel. The way it was wired on mine was they picked up those connections from the pads on top of one of the base RAM modules it is easier to keep track of what goes where than picking them up from vias on the board. The wire used looks like wirewrap wire which is great for things like that but does not like to be bent to often, so that is likely why you are having connection breaking.

Paul.

[MikeSD]

(03-11-2018 02:39 AM)Paul Berger (Canada) Wrote:  Pin 8 is Din and pin 9 is Dout you only need to look at the schematic to verify this. I received a non-working 71B that had two 32K modules inside much like yours. The way it was wired up they broke into chain 0 which is the chain that normally includes the four internal 4K RAM modules and the HPIL adapter. The chain starts off with the the Din pin of U6 (bottom module on right looking from the front) Dout from it goes to Din of U7 (Top right) Dout from U7 goes to U8 (Top Middle) Dout from U8 goes to Din of U9 (Left) and Dout of U9 goes to Din on the HPIL connector. The bottom middle is the OS ROM module and it does not matter because it is a hard configured module.

Paul.

Thanks Paul, this is exactly how mine is wired, except after my 32k RAMs, the Dout runs over to a FORTH module before continuing to HPIL. I'm still assuminv it's a FORTH module, for now. Can't make out the last digit of p/n. The thing that was confusing me was that would bave meant a cut wire on the board, which now mames since with your reply.

I think I have a good understanding on how this all goes now. I numbered the pins in my photo just above. Guess I have it right since 8 an 9 are correct using that convention.

I'm going to strip it all out and put new wires and reflow solded on the left chips, if my 72 year old eyes can still see that well I think I can. One has movement (the chip, not my eye). Want to get the 71B working before reinstalling everything. If it doesn't work, I have another candidate.

Questions

1) I have a couple versions of the museum DVDs if I can find them but I don't recall a schematic. What doc was that in?

2) Looking at my photo above there are 6 mem chips. Is this how they are numbered?
left (Bottom) U6, left (Top) U7, middle (Top) U8, middle (B) U?, right (T) U9, right (B)U?. The right chip in my photo is different from left, I assumed it was the ROM.

3) Any idea what the buzzer mod is for?

Thanks again for the help.

[rprosperi]

(03-11-2018 01:45 PM)MikeSD Wrote:  1) I have a couple versions of the museum DVDs if I can find them but I don't recall a schematic. What doc was that in?

3) Any idea what the buzzer mod is for?

For 1), you probably want to use the "HP-71B Hardware Internal Design Specification (more complete, 164 pages)" document. It contains schematics, board layout, etc. although it is not a full-blown service manual.

For 3), often, buzzers were replaced/modified to make then louder for use outdoors, such as surveying, and also in factory settings. Not sure if these apply here, just a guess.

For 2), I hope Paul is still reading... lol

[Paul Berger (Canada)]

(03-11-2018 01:45 PM)MikeSD Wrote:  I'm going to strip it all out and put new wires and reflow solded on the left chips, if my 72 year old eyes can still see that well I think I can. One has movement (the chip, not my eye). Want to get the 71B working before reinstalling everything. If it doesn't work, I have another candidate.

Questions

1) I have a couple versions of the museum DVDs if I can find them but I don't recall a schematic. What doc was that in?

2) Looking at my photo above there are 6 mem chips. Is this how they are numbered?
left (Bottom) U6, left (Top) U7, middle (Top) U8, middle (B) U?, right (T) U9, right (B)U?. The right chip in my photo is different from left, I assumed it was the ROM.

3) Any idea what the buzzer mod is for?

Thanks again for the help.

The manual with the schematics is "HP-71B Hardware Internal Design Specification (more complete, 164 pages)" The schematics are in chapter 8 figures 8-3 and 8-5. Your board layout looks a little different than mine, so I am guessing the 71B you have is the later version that does not have the metal plate on the back. It is very likely that the schematics in that manual are drawn for the first version so there may be some minor differences between them and your board. On closer examination it would appear that the person that made the mods relocated a couple components to make space for the Ram modules.

The ground wire on the RAM is connected to the pad where the emitter of the transistor that drives the buzzer was. The transistor and inductor are now tucked in behind the battery compartment the red wire from from the emitter of the power transistor would be 5V. the emitter of the TO-92 transistor appears to be connected to the anode of diode CR7 which is ok that is ground. The base should be connected to the cathode of that diode but I cannot tell from the picture. So the buzzer mod is to relocate a couple components.

U6 is left bottom U7 is left top U8 middle top U9 is bottom right and top right would be a module that was added, probably ROM. looking closer the bottom right does not look like one of the original 4K module where U9 would normally be, so perhaps they sacrificed one of the original 4K modules to put in another ROM. You will note that the left and middle modules all have the same circuit board but the bottom middle has different solder blob jumpers I am guessing because it is ROM.

There is a better spot where they could have located the two RAM modules it requires slightly longer wires but get them out of the way, I will post a picture later. I am not sure where they might have placed the module you labelled as FORTH.

[MikeSD]

You are right. Never noticed. There is a diff. That top device is the one that is loosish (see comparison below) That is the chip my 32k RAM daisy chain from. if ROM wonder what it is. Maybe another app. It's marked 5180-2918.

I found a schematic. It shows 5 mem chips. Mine has 6. Based on differences, I assumed the 2 I have on right in my pic are ROMs. But now I think 5 are RAM and the top is Rom or an app chip. I'll do a little more checking around. I know I have the IDS on my computer. I'll take another. Maybe the schematic there is different.

NOTE: Wonder if anyone has an original service manual to sell. I have a copy but...

Mine is metal back. I have half dozen non-working ones I need to get around to one of these days.

My IDS only has block diagrams and nonpin-outs. Only names. Guess I have a brief version. Still I think I have enough information to tackle this.

Thanks

[Paul Berger (Canada)]

(03-11-2018 03:17 PM)MikeSD Wrote:  I found a schematic. It shows 5 mem chips. Mine has 6. Based on differences, I assume the 2 I have on right in my pic are ROMs. I'll do a little more checking around. I know I have the IDS on my computer. I'll take another. Maybe the schematic there is different.

NOTE: Wonder if anyone has an original service manual to sell. I have a copy but...

Mine is metal back. I have half dozen non-working ones I need to get around to one of these days.

My IDS only has block diagrams and nonpin-outs. Only names. Guess I have a brief version. Still I think I have enough information to tackle this.

Thanks

Yes I think the two on the right in your picture are ROMs too. See my previous post the document I mentioned is the hardware IDS and it is in the MoHPC collection.

I only have a PDF of the service guide apparently sourced from hpmuseum.net unfortunately the schematics in that PDF where cut up, but they are complete in the IDS found on the MoHPC collection.

Yes only pin names numbering was arbitrary based on +5 (Vdd) being pin 1.

Paul.

[MikeSD]

Here is a closeup of that topndevice. It doesn't appear to have the 3-7 lines like on RAM. Could be under but why? Anyway it does have part number that might help identify what it is.

[Dave Frederickson]

The Service Manual along with a copy of the IDS can be found here,

http://www.hpmuseum.net/exhibit.php?hwdoc=118

I agree that the 5061-723? chip is likely the F/A ROM. It would be a logical choice for a hard-wired ROM mod.

The question is what's the module on top of U9?

Mike, can you post a pic of the other side of the F/A module and the white sticker. HP left a sticker in my 71 after it was repaired as a form of repair history. I'm curious as to what they did to this 71.

Dave