HP-11C disassembly

[Tony]

Hi!
My HP-11C has a lot of dust behind the display.
I can remove the back cover but I cannot remove the printed curcuit board! It is attached firmly but I cannot see any screws. Manufacturing year is 1985, USA.
What do I have to do to get to the display?
Thanks for help, Tony

[Vieira, Luiz C. (Brazil)]

Hi;

there are two voyager basic types. The earlier models have the KBD assy and a display separate assy (the second one allows display cleanning, but it has flex circuit board, and it is a lot hard to maintain...). The new versions have one only PCB, and everything is built on it. If this is yours (it seems to me), the only two ways I know to clean the disaply are
by using compressed air (avoid it because of static electricity) OR
removing all plastic heat-molded rivets. It's time consuming and tiring, but if you really need to clean de display window, that's the only way I know.

Not that much helpfull, I know, but may let you think about it.

Cheers.

[Raymond Del Tondo]

Hi,

cutting the heat stakes is a relatively easy job,
if you have the right tool;-)

I usually take a very flat and sharp Revell hobby tool,
which has four different shaped blades.
This tool is made for cutting plastic edges.

It may be of use that you can leave the bottom row of stakes intact, it should suffice to lift the PCB a bit,
and use a photo lens air cleaner to get rid of the dust.
This way you don't need to re-heat the stakes before you reassemble the calc. The bottom row stakes give enough stability to the PCB to sit tight inside the housing.

Regards,

Raymond

[O.J.M.]

I once cleaned out the display on my HP15C by gently lifting off the aluminum bezel on the front of the unit. In my case it seemed to be the best choice since the double-sided sticky tape that held it down had already begun to come unglued and lift up on its own. The clear plastic lens over the LCD comes off with it. This gives you access to clean off dust withou having to open up the calculator and put its internals at risk. One must take care not to lose a small spring that grounds the aluminum piece to the unit's ground plane. I then reglued the metal piece with more double-sticky tape. This method may risk some cosmetic damage to the unit, but it avoids having to take it all apart and possibly damage it. (I would rather have an ugly calculator that works, than a pretty one that doesn't.)

[Tony]

Thanks Luiz!!
Thanks Raymond!!
Thanks ojm!!

Your answers resolve my problem.

[David Smith]

I can definitely recommend NOT cutting the heat stakes loose. It is very difficult and time consuming to do properly and to get the machine back together again without causing a squishy keyboard can be a challenge.

Also do NOT use an air compressor. Almost all of them spew oil and dirty water along with air. Try canned lens/keyboard cleaning "air".

If you elect to try removing the front bezel you might try to get the commercial product called "UnDu". It is just the solvent heptane in an expensive little bottle. Heptane causes adhesives to temporarily loose their stick. When it (quickly) drys the stick returns. Do not get it on the keyboard background as it can leave "water" marks behind.

[Vieira, Luiz C. (Brazil)]

Hi;

I am very curious about this "UnDu" solvent. I am almost sure there is no similar product in Brazil, but I'll try to find it anyway.

How expensive is it? If I can buy it, would you give some tips on how to use it? I once tried to remove the front bezel af an old voyager, and I did not get success (I stopped when it as about to bend). I have an old HP11C and I want to remove its back label, because I printed a new one and I want to put it there. How to remove the almost-erased, full-of-scratch, old one safely? Would this "UnDu" help doing it? There is no single gap between the back label and the inner glue; is it possible to remove without bending?

Wow! So many questions... Any answers?

Thanks.

[David Smith]

UnDu is just the solvent heptane. It is sold in fancy little one ounce bottles for around $5 and larger ones (3 oz) for around $10. Considering a liter at a chemical supply house can be had for 5 dollars or so, it has quite a markup. Also many types of rubber cement thinner are sold in hardware stores for a few dollars a pint are just heptane (some are hexane).

I would try soaking a stong thin string in it (and mayby placing a few drops under the edge of the bezel) and using it like a cheese cutter to separate the adjesive (works great on calculator front labels). When fixing card readers I place a drop on an small Swiss army knife blade and lift the back label corners.

Again, keep it off the keyboard background. It can leave water marks behind. Does not seem to affect the cases or labels though.

[Tony]

Hi David,
Well, I did in fact cut off all the stakes. After this it was easy to remove the circuit board and clean the display and the keys as necessary. Also, I had no trouble to put things together again. In order to avoid the squishy keyboard the curcuit board needs to be supported from the back. I used stripes of packaging foam and the back cover now holds the curcuit board firmly in place. Woeks pretty good.
Tony

[John]

now i know how to get at the guts of a calculator, but what i want to know is where oh where do you 11c owners get replacement batteries???

[Randy Sloyer]

If you are in the states:

Wal-Mart

K-Mart

RadioShack

for starters. At the "marts", go to the watch counter and ask for 357's (you don't get batteries when asking in sporting goods...)

or 44's
or 76's

1.5 volt alkalines are fine, should be around $2.00-$3.00 each. There are people selling packs of 10 for $5.00 on Ebay, but who know how old they are. Besides, if you have only 1 11C, thats about a 30 year supply, on average.

[David Smith]

A company called "Vinnic" sells very cheap batteries from China. Cards of 10 "LR44" batteries for around $2.00 - $2.50 These are proably what are showing up on Ebay. BTW, they seem to be rather good batteries. I have used LOTS of them without problem.

[Randy Sloyer]

Thanks David. That is good to know. I had seen the deals for $4-5 for 10 and thought the old "if it sounds too good to be true..." I will check out the brands as it does hurt a bit forking over $10 or so for a new set of batteries.

[John]

thanks, randy. didn't realize that 357, 44, and 76 were all equivalent and acceptable. case shows 871B.

[Randy Sloyer]

Battery numbers are now the 1950's equivalent of tubes. You know, those old things that glowed in the dark and warmed your room in the winter. Pick a number and you can find a substitute for it. Not that it means a thing, but I have never heard of a 871B. So it was probably a substitution of a substitution. Which bears evidence to the fact that just about any battery that generates between 1.35 to 1.5 volts and is the same physical size will work. The only problem I have seen with the lower voltage batteries was on a 42S when using the infrared printer interface. The batteries were weak and the current required by the i/r diode managed to drop the supply voltage below the static ram retention level and bingo, instant cleared memory. I doubt you would see a problem like this with an 11C.

[Ellis Easley]

I have an old (~1968) 50 MHz HP oscilloscope which is about 1/2 tubes and 1/2 transistors, it draws 750 Watts so I only use it in the winter. Also, it has a high voltage transformer that operates at about 40 kHz. As it drifted, it would turn on a TV I used to have which had an ultrasonic remote control. Since the "on" button was also the "volume up" button, the TV would turn on and get louder and louder. Once, in a pinch, I taped a bedroom slipper to the front of the TV to cover the remote control microphone.

[James M. Prange (Michigan)]

Good one.

Back around the mid-'70s, I assembled a Heathkit TV, including an ultrasonic remote control. Pretty nifty, but it took me a while to scrape up the money to buy a cabinet to put it in. But after a few weeks, it would, now and then, mysteriously turn itself on or off, change channels, turn the volume up or down, or adjust the colors. I spent some time troubleshooting that thing, and soon realized that disconnecting the microphone seemed to solve the problem, and then, eventually, I noticed that with the microphone connected, it sometimes went bonkers when a cricket chirped nearby. The solution was to tape a piece a cloth in front of the microphone until I finally got a cabinet to put it in.

Regards,

James

[Randy Sloyer]

You're not going to believe this, but... you where not alone. This was not an isolated incident with the GR-900. Back in the 1970's I worked for Heath for a bunch of years. Ultrasonic technologies were pretty crude. Heath decided to go with low ultrasonic range transducers, I seem to remember it in the 20-30 khz range. Some of the lower end codes were actually audible to some people (me included!). It kept the costs lower and used common transducers. The only problem was, the transmitters and receivers used LC circuits and had no real time base and always drifted off frequency. So they where not very reliable and of course when the receiver side went wacko, yep, all sorts of things would make the TV seem possessed. Remote control was always a weak point with Heath TV's. I think they got them straightened out by going digital after the GR-2000, but I was gone by then.

[Ellis Easley]

My TV was an RCA. Once a co-worker had trouble with her RCA TV remote control and asked me to see if I could fix it. It was IR but only had four buttons like my ultrasonic one. It turned out that one of the solder joints on the LED had come loose. After repairing it, I used a photocell and oscilloscope to make sure it was working. It operated on the same frequencies as my ultrasonic remote.

That ultrasonic remote ran for the whole life of the TV on the original pair of Duracell AA's that came with the set.

When I was in high school (early 70's) a friend had a portable TV with remote control which had a mechanical, VHF only tuner driven by a motor. One position was "TV off". I don't remember if it had remote control of the volume. The remote control unit contained a bar of aluminum which was struck like a tuning fork when you pressed a button. You could hear some frequencies when it was struck, but I wonder if the TV responded to higher harmonics to make it less susceptible to common sounds? I believe the guy showed me that rattling keys in front of the set would make it change channels.