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HP97 The journey begins
01-11-2019, 12:46 AM
Post: #1
HP97 The journey begins
Hi all,

The time has finally come to start repairs to a HP97.

I always wondered, saying (a HP) or (an HP) ???
I say H as Haytch, not Aycth, so a HP sounds better, tomaytoes and tomartoes I guess Smile

Anyway, the unit is almost totally dead. Just the low battery light on and the card reader motor running continuously. The printer motor is "ticking" suggesting that it is trying to turn on then immediately off again.

This will take some time to get going one way or another but will be an interesting challenge.

I asked a little while back about opening up a battery case to replace batteries, but no answers so not sure if it has been done

The two case halves that I have were glued together, but not continuously around the join. With some small inwards pressure on one half, I was able to insert a small flat bladed screw driver into a gap and widen it slightly. I then used a 2nd driver to open it a bit further, then alternatively shift them bit by bit further along the widening gap. I carefully continued this along the long case edge trying not to distort it and I could hear the glue spots break apart as I went. Eventually it separated.

One of many questions to follow I'm sure, but there are 2 battery terminals on the battery pack. Can anyone please verify that the terminal near the centre is the +ve and the other nearer to the case edge is the -ve? I want to power the calculator directly with my bench power supply, but don't want to fry anything.

I'm sure they will be needed, so I ordered some O-rings for the card reader from the US for a few $ and they arrived in short time.

When the dealer finally opens again ???, I am buying myself a late Xmas present, a Rigol MSO digital oscilloscope which should help things along.

cheers

Tony


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01-11-2019, 01:26 AM
Post: #2
RE: HP97 The journey begins
Yes, the center-most contact is (+) and the outer (-). The pack is 4 x 1.2V NiCD cells, so 4.8-5V is probably correct.

Rebuilt TopCat battery packs are common (always available on eBay) and it's just 4 cells in series.

Quote:I say H as Haytch, not Aycth...

I have wondered how one might spell 'Haytch' Smile

As I use 'Aytch', "an HP" is more comfortable here.

Which of course is why there is a debate about this...

--Bob Prosperi
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01-11-2019, 01:45 AM
Post: #3
RE: HP97 The journey begins
(01-11-2019 01:26 AM)rprosperi Wrote:  
Quote:I say H as Haytch, not Aycth...

I have wondered how one might spell 'Haytch' Smile

As I use 'Aytch', "an HP" is more comfortable here.

Which of course is why there is a debate about this...

You'd think that Aussies (assuming "haytch" for h is the standard Australian pronunciation, if there is in fact a standard) would write "a HP," but I've noticed the odd inconsistency with English speakers in general, like writing "an historic event," even though the h in history is not silent in most dialects... what's up with that?
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01-11-2019, 02:12 AM
Post: #4
RE: HP97 The journey begins
Hi all,

After just half hour of poking around, repairing a few dodgy solder joints and a bent CPU board connector, sill dead.

There was another CPU board in the box, which I didn't hold much hope for as it had no static protection, but on replacing it and making sure all pins were in good contact, it fired up and seems to work ok, accepts and runs programs too.

I set the input voltage to just where the low battery LED extinguished, and no nasty current flow from the power supply, about 160mA (no battery connected), and changing the display from 0.00 to -8.888888888 -88 drew an extra 60mA or so. The chips seem cool and happy, so that seems a good start.

Alas, the printer and card reader are not happy at all, so I think this is where the fun will start.

cheers

Tony


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01-11-2019, 04:06 AM
Post: #5
RE: HP97 The journey begins
Does the printer try to do anything? With no paper in it pressing the paper feed button should cause the print head to move left about 1/3 of its travel, this is of course assuming that the wires or the button have not broken odd their connectors. if they are not connected correctly the printer will not work properly either. I had one with a marginal PIK that when cold the printhead would barely get off the right margin, but after it was on for a while it would print normally.

You will find lots of tutorials for the card reader, the trick to getting out the cable without damaging it is to slip a piece of stiff plastic in between the contacts and the cable, I use pieces cut from blister packs.

Paul.
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01-11-2019, 05:51 AM
Post: #6
RE: HP97 The journey begins
(01-11-2019 04:06 AM)Paul Berger (Canada) Wrote:  Does the printer try to do anything? With no paper in it pressing the paper feed button should cause the print head to move left about 1/3 of its travel, this is of course assuming that the wires or the button have not broken odd their connectors. if they are not connected correctly the printer will not work properly either. I had one with a marginal PIK that when cold the printhead would barely get off the right margin, but after it was on for a while it would print normally.

You will find lots of tutorials for the card reader, the trick to getting out the cable without damaging it is to slip a piece of stiff plastic in between the contacts and the cable, I use pieces cut from blister packs.

Paul.

Thanks Paul,

The first CPU board made the card reader and printer do weird things, but none of that with the second board. The printer carriage seems to have tight spots as I manually but carefully wind it along the worm drive. It is all full of gunk so I have stripped it down to give it a clean and a bit of lube. The motor was trying to drive it but it too slowed down as it travelled left.

I did manage to get the ribbon cable out after I figured out what was required. I used some folded aluminium from a soft drink can which is nice a smooth. It appears that the thickness of the "tool" is important. Too thin and the cable comes out but the tool gets stuck in and another tool is required. If the thickness is right then it will raise the rear of the connectors away from cable by pushing up on their leading edges. Then, if you make sure you don't push it in too far, the cable slips right out.

I'll have a good read of the service manual for the printer.

When it is reassembled, I will try out what you mentioned. It is interesting that it moves that far before figuring out there is no paper. The magnetic carriage return switch must keep the reed switch shorted for a bit of the initial carriage travel. I haven't figured out how the paper out mechanism works, it looks like 2 wires that go to 2 metallic plates that are close to or rub up against the paper.

cheers

Tony
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01-11-2019, 05:56 AM
Post: #7
RE: HP97 The journey begins
(01-11-2019 01:26 AM)rprosperi Wrote:  Yes, the center-most contact is (+) and the outer (-). The pack is 4 x 1.2V NiCD cells, so 4.8-5V is probably correct.

Rebuilt TopCat battery packs are common (always available on eBay) and it's just 4 cells in series.

Thanks Bob, that worked.

cheers

Tony
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01-11-2019, 07:57 AM
Post: #8
RE: HP97 The journey begins
One spic'n'span printer unit.

I haven't tested it yet, but the carriage runs back and forth along the worm gear quite nicely now and the motor doesn't strain at all.

The motor with capacitor measure 12 ohms which is 3 above the minimum so should be ok. C2 across the motor seems to polarised but I cannot find a part listed in the service manual. This seems odd, in that the motor has the voltage reversed when the motor has to home the print head.

I figured out the paper out mechanism Smile

cheers

Tony


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01-11-2019, 08:40 AM
Post: #9
RE: HP97 The journey begins
Back again,

Things are moving faster than I thought.

I have completely stripped the 97 down except for the card reader. Except from some dirt and dust inside, its pretty clean.

A few problems I found were due to age mixed with mishandling of circuit boards.

I have seen these bent pins on a few boards and I think it is caused by being in a hurry and not checking placement when re-connecting the boards. Depending on the pin, if undetected, it might lead one to think the board has chip problems.

The other problem is one where someone has handled the boards with dirty or sweaty fingers and has caused the corrosion. It's a bit hard to see in the image, but the finger prints really stand out on the blackened areas.

It all still works, so hopefully just a spring clean.

Card reader next...

cheers

Tony


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01-11-2019, 11:19 AM
Post: #10
RE: HP97 The journey begins
Hi all,

Stripped, cleaned and after 2 goes, replaced the gunk that was left of the card drive wheel with o rings.

I powered the motor with about 4 volts and it was quite happy pulling the card through.

Enough for one day, tomorrow, I can start reassembling and see what happens.

cheers

Tony


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01-11-2019, 01:18 PM (This post was last modified: 01-11-2019 01:20 PM by Paul Berger (Canada).)
Post: #11
RE: HP97 The journey begins
(01-11-2019 05:51 AM)teenix Wrote:  When it is reassembled, I will try out what you mentioned. It is interesting that it moves that far before figuring out there is no paper. The magnetic carriage return switch must keep the reed switch shorted for a bit of the initial carriage travel. I haven't figured out how the paper out mechanism works, it looks like 2 wires that go to 2 metallic plates that are close to or rub up against the paper.

cheers

Tony
It moves that far to actuate the paper feed which is the only way to get paper in. You may have noted a ridge running along the plastic sleeve over the shaft of the feed roll which also has teeth on the right end that mate with teeth on the right roll to form a ratchet. That ridge rides in a groove in the print head carrier, so as it moves left the sleeve is rotated upwards far enough that the ratchet jumps up 2 teeth and then when the carrier returns, it is rotated downwards which engages the teeth and feeds the paper forward.

While I think of it it seems common for the tire on the feed rolls to get hard and smooth causing irregular feeding of the paper. I have replaced them with a slice of silicon tubing. If you do that, there is a ridge under the tire you will likely need to carve off.

There is also the idler gear which often falls apart I have a spare made of aluminum if you need one.

Paul.
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01-11-2019, 01:25 PM
Post: #12
RE: HP97 The journey begins
(01-11-2019 08:40 AM)teenix Wrote:  Back again,

I have seen these bent pins on a few boards and I think it is caused by being in a hurry and not checking placement when re-connecting the boards. Depending on the pin, if undetected, it might lead one to think the board has chip problems.


cheers

Tony

I have managed to straighten out those pins, however I have also broken them trying to do so if they are making contact its best to leave well enough alone.

Paul.
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01-12-2019, 02:01 AM
Post: #13
RE: HP97 The journey begins
(01-11-2019 01:25 PM)Paul Berger (Canada) Wrote:  With no paper in it pressing the paper feed button should cause the print head to move left about 1/3 of its travel

Paul

I stripped the keyboard down this morning and cleaned any residue that accumulated under the buttons over the years, then scrubbed up the case and buttons and put it all back together.

It powered up ok, so I got the refurbished battery pack and put it in and as I don't have a 97 charger, I set my bench supply to give it about 180mA. Should take the rest of the day to charge.

The printer did as you mentioned without paper, the carriage travelled a cm or so then returned.

I haven't fully assembled it yet. When the battery is fully charged, I'll try out the printer and card reader.

(01-11-2019 01:25 PM)Paul Berger (Canada) Wrote:  I have managed to straighten out those pins, however I have also broken them trying to do so if they are making contact its best to leave well enough alone.

Paul.

Me too, but as you rightly say, if it ain't broke, don't fix it

cheers

Tony


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01-12-2019, 06:22 AM
Post: #14
RE: HP97 The journey begins
Hi all,

Struck a snag.

The card reader accepted cards ok for about 2 passes. then although the motor was still running, until an error occurred, it failed to pass any more cards.

I thought maybe the new o rings were slightly too large. I measured them with a vernier and the outside diameter is 250 thou (1/4 inch)

I'm not sure what to expect with card tensions, but too me the card seems a bit stiff when trying to pull it through the slot against the drive wheel with the motor detached. I thought this would be quite easy with just a small amount of friction.

When I originally pulled the card reader apart yesterday, the worm drive could be removed easily by sliding it off the motor shaft. Is this normal, or has the bushing broken down? It is reasonably loose on the motor shaft which is why the card stops.

Any help appreciated

cheers

Tony


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01-12-2019, 06:57 AM
Post: #15
RE: HP97 The journey begins
Sorry, jumped in too quick...

Eccentric Cam

I read about it the other day but too much on my mind and the meaning didn't sink in. It does alter the drag on the card a bit so will try the current test when I sort out the shaft issue.

cheers

Tony
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01-12-2019, 07:42 AM
Post: #16
RE: HP97 The journey begins
Just did a forum search and watched Geoff Quickfalls dampening shaft repair video, so will have to experiment with some wires.

cheers

Tony
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01-12-2019, 09:08 AM
Post: #17
RE: HP97 The journey begins
Hi Tony,
There are several approaches.
Somebody suggested a thin and tiny layer of wrapping foil others super glue or also the silicone solution ...
http://www.hpmuseum.org/repclutc.htm
Here is one where that guy used a WD40 straw
http://www.hpmuseum.org/cgi-sys/cgiwrap/...ead=237065
As there are card readers for other HP machines and different solutions you should see which one is the appropriate every time you do the clutch fix
Good luck
Andi
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01-13-2019, 03:00 AM
Post: #18
RE: HP97 The journey begins
Hi all,

I sprayed some circuit board lacquer onto the back of the display PCB to protect it. This is the stuff that you can solder through if necessary.

It was one of those nights where something is on your mind and you cant sleep from trying to solve it. The problem was the rotted dampening shaft material. I though of all sorts of solutions and ended up considering the silicon approach, but I didn't like the idea of the mess with small parts and trying the centralise everything, then hold it there somehow while it set. Some non liquid form of repair seemed to me to be the best approach.

My thought was, this coupling is supposed to dampen vibration so if the assembly is off centre then it will vibrate anyway. The coupling (I think) is also there to provide a release mechanism if the card seizes in the slot and therefore save the motor from burning out or stripping gears. HP's solution was elegant but difficult to mimic for a home constructor.

After some searching around and some guess work I went down the local electronics hobby shop this morning and bought some cable that I thought might do the job.

As it turned out, and I am still gob smacked, the first cable I tried was almost perfect. It took three goes to get a working coupling, but the last try only took under 10 minutes.

All you need is the following...

A piece of 75 ohm RG58 coax (75c per meter)
Stanley blade
A 5/64 drill bit
Preferably a bench drill.

Method...

Cut about 2 inches of the outer sheath off and strip the underlying wire braid
Use the Stanley blade to cut the inner translucent wire sheath at the same point and pull the sheath off.

Unless your motor has a different shaft size, the inner hole fits perfectly onto it and provides lots of drag and can be easily removed.

Next, place the drill bit into the bench drill and have it at a "medium" speed.
Taking care here, hold the translucent sheath vertical and gently push it up against the rotating drill bit.
You only need to remove about 5mm of material from the inner hole, any more and the drill may drift off centre. The inner hole will serve as a drill guide.

Once done, if the hole is out of centre, discard it and start again. Look through the translucency in bright light and you will see the drill path. It should be even all around.

Place the worm drive against the sheath, then with the Stanley blade cut off what you think is enough for it to sit on the shaft end.

On the other end, cut the sheath to the length that will let the motor sit in position without binding it.

Finally, push the motor shaft onto the sheath and you are done.

As this assembly is so short, it has good mechanical strength, so I did not replace the aluminium sleeve as I don't think it is needed.

I tried it with some cards just by powering up the motor from my bench supply and the cards went through quite nicely.

I haven't tested it by reading/writing but will do so later today. Hopefully all ok.

cheers

Tony


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01-13-2019, 03:31 AM
Post: #19
RE: HP97 The journey begins
(01-13-2019 03:00 AM)teenix Wrote:  Place the worm drive against the sheath, then with the Stanley blade cut off what you think is enough for it to sit on the shaft end.

On the other end, cut the sheath to the length that will let the motor sit in position without binding it.

Just thinking, the original coupling was the same width as the aluminium sleeve, so that can be used as a length guide. The aluminium sleeve can also be used as a guide for the blade to cut up against so you get a nice right angle cut at each end of the sheath.

One minor thing, the drill is angled at the end where as the original coupling was moulded to fit the machined end of the worm drive, so make sure the shoulder on the worm drive can butt up against the end of the new coupling.

Seems fiddly, but in practice, not that bad.

cheers

Tony
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01-13-2019, 04:58 AM
Post: #20
RE: HP97 The journey begins
I connected everything electrically and holding the battery in place, still working.

The card reader is just floating until I know it works.

I switched to PGM mode and wrote 5 + 7 enter and put in a blank card and through it went.

I powered down, then up again in RUN mode, passed the card, pressed R/S and I'll be, 12 popped up on he display.

I'll reassemble properly and see how it goes. I don't have the special alignment tool for the card reader so I'll just have to align it to the screw head indents in the plastic where is was originally screwed down.

cheers

Tony
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