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HP 71b repair advice - won't power on with batteries or on AC adaptor
06-07-2021, 06:19 AM
Post: #1
HP 71b repair advice - won't power on with batteries or on AC adaptor
I have 2 plastic backed 71b units with battery terminal corrosion and breakage, one bad and one worse. They won't power on with batteries and I was hoping they would work on the AC adaptor but no go with that either (I tested a working 71b without batteries on the same adaptor so the adaptor is fine).

Other than the battery terminal corrosion they look in reasonable condition and keyboards feel ok.

I haven't been able to locate much information on what to look for or try in this situation (I found some reset articles but the problem unit in these was powering up but freezing and mine don't power up at all).

How hard is it to take the 71b (plastic back) apart and then are there any easy test/fix points?

Could it just be the AC adaptor connection is corroded too or is it more likely to have damaged something else first?

Has anyone had much luck repairing the 71b?

TIA, dmh
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06-07-2021, 07:29 AM
Post: #2
RE: HP 71b repair advice - won't power on with batteries or on AC adaptor
If you had been in Germany, I would have said "come on over and let's look at it" - but that's obviously not an option...

You can find the repair manual with the link below, that should help you with how to open and peek inside. Some electronics experience is required if you want to repair!

AND a Torx 6, don't try without!!

Documentation

I have repaired a few of these after corrosion - Battery-Leak - and it can be very tricky.

You can have anything from Copper traces being corroded to oblivion or the ZEBRA which connect top and bottom on the Plastic-Back model - and many more, peeking should give you some hints.

The ZEBRA can be replaced with soldering short wires from top to bottom "clam", if you are good with an iron and have the kit to solder "thin" wires on small pads.

If you like you can drop a photo of what you find here on HPMUSEUM and there will surely be some commentary from the 71B experts on this forum

(06-07-2021 06:19 AM)dmh Wrote:  I have 2 plastic backed 71b units with battery terminal corrosion and breakage, one bad and one worse. They won't power on with batteries and I was hoping they would work on the AC adaptor but no go with that either (I tested a working 71b without batteries on the same adaptor so the adaptor is fine).

Other than the battery terminal corrosion they look in reasonable condition and keyboards feel ok.

I haven't been able to locate much information on what to look for or try in this situation (I found some reset articles but the problem unit in these was powering up but freezing and mine don't power up at all).

How hard is it to take the 71b (plastic back) apart and then are there any easy test/fix points?

Could it just be the AC adaptor connection is corroded too or is it more likely to have damaged something else first?

Has anyone had much luck repairing the 71b?

TIA, dmh
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06-07-2021, 12:29 PM (This post was last modified: 06-07-2021 12:46 PM by Etienne Victoria.)
Post: #3
RE: HP 71b repair advice - won't power on with batteries or on AC adaptor
Depending on your Hp71B, you might find two (as far as I know) different versions of the 71B innards :

- Earlier models with a quality, reliable (on my units) soldered flex cable: I would advise to repair these with an appropriate flex cable.

- Later models with the cost saving, not soldered, el cheapo, plasticky, Hp41-like, so-called "Zebra strip" : these have less clearance to insert and fold a flex cable so I would advise to solder top to bottom wires directly.

Below a couple images, to show the different layouts.


V1: https://1drv.ms/u/s!Aj6GqoriKYJuhYMkhkcT...w?e=bg2jgD

V2: https://1drv.ms/u/s!Aj6GqoriKYJuhYMlFEoK...w?e=sUkf41

The latter has this prone-to-fail connector inbetween the two halves :

http://etiennevictoria.com/Titan_zebra/grand-1.html
http://etiennevictoria.com/Titan_zebra/grand-2.html


Etienne
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06-07-2021, 12:48 PM
Post: #4
RE: HP 71b repair advice - won't power on with batteries or on AC adaptor
(06-07-2021 12:29 PM)Etienne Victoria Wrote:  Depending on your Hp71B, you might find two (as far as I know) different versions of the 71B innards :

- Earlier models with a reliable (on my units) soldered flex cable: I would advise to repair these with an appropriate flex cable.

- Later models with the cost saving, not soldered, el cheapo, plasticky, Hp41-like, so-called "Zebra" strip : these have less clearance to insert and fold a flex cable so I would advise to solder top to bottom wires directly.

Below a couple images, to show the different layouts.


V1: https://1drv.ms/u/s!Aj6GqoriKYJuhYMkhkcT...w?e=bg2jgD

V2: https://1drv.ms/u/s!Aj6GqoriKYJuhYMlFEoK...w?e=sUkf41

The latter has this prone-to-fail connector inbetween the two halves :

http://etiennevictoria.com/Titan_zebra/grand-1.html
http://etiennevictoria.com/Titan_zebra/grand-2.html


Etienne

Thanks. I think that’s the difference between the metal back and plastic back or is it not that simple to identify?

Unfortunately I can’t see the images you’ve attached. A common issue I find here. I’ve tried different browsers but no luck.
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06-07-2021, 12:54 PM
Post: #5
RE: HP 71b repair advice - won't power on with batteries or on AC adaptor
Thanks for letting me know. I have updated the links which should hopefully work now.

I cannot certify there is a full correlation between the metal vs. plastic back and the zebra vs.flatflex versions as I only have 6 units here.

Good luck for your repair.

Etienne
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06-08-2021, 04:19 AM
Post: #6
RE: HP 71b repair advice - won't power on with batteries or on AC adaptor
(06-07-2021 07:29 AM)KimH Wrote:  If you had been in Germany, I would have said "come on over and let's look at it" - but that's obviously not an option...

You can find the repair manual with the link below, that should help you with how to open and peek inside. Some electronics experience is required if you want to repair!

AND a Torx 6, don't try without!!

Documentation

I have repaired a few of these after corrosion - Battery-Leak - and it can be very tricky.

You can have anything from Copper traces being corroded to oblivion or the ZEBRA which connect top and bottom on the Plastic-Back model - and many more, peeking should give you some hints.

The ZEBRA can be replaced with soldering short wires from top to bottom "clam", if you are good with an iron and have the kit to solder "thin" wires on small pads.

If you like you can drop a photo of what you find here on HPMUSEUM and there will surely be some commentary from the 71B experts on this forum

(06-07-2021 06:19 AM)dmh Wrote:  I have 2 plastic backed 71b units with battery terminal corrosion and breakage, one bad and one worse. They won't power on with batteries and I was hoping they would work on the AC adaptor but no go with that either (I tested a working 71b without batteries on the same adaptor so the adaptor is fine).

Other than the battery terminal corrosion they look in reasonable condition and keyboards feel ok.

I haven't been able to locate much information on what to look for or try in this situation (I found some reset articles but the problem unit in these was powering up but freezing and mine don't power up at all).

How hard is it to take the 71b (plastic back) apart and then are there any easy test/fix points?

Could it just be the AC adaptor connection is corroded too or is it more likely to have damaged something else first?

Has anyone had much luck repairing the 71b?

TIA, dmh

Thanks. After looking at the photos popping over is still tempting :-).

That Zebra connector looks very fragile!

I only have a T10 and T15 so will need to source a T6.

Is there much risk of damaging anything else if I open to have a look? Just evaluating whether it is worth it. I don't have soldering tools or experience.
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06-08-2021, 05:19 AM
Post: #7
RE: HP 71b repair advice - won't power on with batteries or on AC adaptor
(06-08-2021 04:19 AM)dmh Wrote:  
(06-07-2021 07:29 AM)KimH Wrote:  If you had been in Germany, I would have said "come on over and let's look at it" - but that's obviously not an option...

You can find the repair manual with the link below, that should help you with how to open and peek inside. Some electronics experience is required if you want to repair!

AND a Torx 6, don't try without!!

Documentation

I have repaired a few of these after corrosion - Battery-Leak - and it can be very tricky.

You can have anything from Copper traces being corroded to oblivion or the ZEBRA which connect top and bottom on the Plastic-Back model - and many more, peeking should give you some hints.

The ZEBRA can be replaced with soldering short wires from top to bottom "clam", if you are good with an iron and have the kit to solder "thin" wires on small pads.

If you like you can drop a photo of what you find here on HPMUSEUM and there will surely be some commentary from the 71B experts on this forum

Thanks. After looking at the photos popping over is still tempting :-).

That Zebra connector looks very fragile!

I only have a T10 and T15 so will need to source a T6.

Is there much risk of damaging anything else if I open to have a look? Just evaluating whether it is worth it. I don't have soldering tools or experience.

The images from Etienne are very good for you decision.

The Zebra images show how they should NOT look, they are supposed to be the same shining thin gold connections from one end to the other.

The one with the flex-cable is the metal back version - lots more screws to hold things together and in place. Not like what you have.

If you don’t have the experience - or know one who has - you will likely see what is in the pictures plus the corrosion (green) which you can clean with vinegar. But that’s the end…

The likelihood that they would recover from a repair is actually quite high, as mentioned a have done a few, mainly fixing corrosion or modifying module configuration RAM/ROM, I have yet to see one I couldn’t recover (unless display was dead… that one is hard)
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06-08-2021, 01:58 PM
Post: #8
RE: HP 71b repair advice - won't power on with batteries or on AC adaptor
(06-08-2021 05:19 AM)KimH Wrote:  
(06-08-2021 04:19 AM)dmh Wrote:  Thanks. After looking at the photos popping over is still tempting :-).

That Zebra connector looks very fragile!

I only have a T10 and T15 so will need to source a T6.

Is there much risk of damaging anything else if I open to have a look? Just evaluating whether it is worth it. I don't have soldering tools or experience.

The images from Etienne are very good for you decision.

The Zebra images show how they should NOT look, they are supposed to be the same shining thin gold connections from one end to the other.

The one with the flex-cable is the metal back version - lots more screws to hold things together and in place. Not like what you have.

If you don’t have the experience - or know one who has - you will likely see what is in the pictures plus the corrosion (green) which you can clean with vinegar. But that’s the end…

The likelihood that they would recover from a repair is actually quite high, as mentioned a have done a few, mainly fixing corrosion or modifying module configuration RAM/ROM, I have yet to see one I couldn’t recover (unless display was dead… that one is hard)

So what supports the Zebra and the spacer? How is it removed?

Do you have any photos showing it still installed?
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06-08-2021, 02:37 PM
Post: #9
RE: HP 71b repair advice - won't power on with batteries or on AC adaptor
(06-08-2021 01:58 PM)dmh Wrote:  
(06-08-2021 05:19 AM)KimH Wrote:  The images from Etienne are very good for you decision.

The Zebra images show how they should NOT look, they are supposed to be the same shining thin gold connections from one end to the other.

The one with the flex-cable is the metal back version - lots more screws to hold things together and in place. Not like what you have.

If you don’t have the experience - or know one who has - you will likely see what is in the pictures plus the corrosion (green) which you can clean with vinegar. But that’s the end…

The likelihood that they would recover from a repair is actually quite high, as mentioned a have done a few, mainly fixing corrosion or modifying module configuration RAM/ROM, I have yet to see one I couldn’t recover (unless display was dead… that one is hard)

So what supports the Zebra and the spacer? How is it removed?

Do you have any photos showing it still installed?

I don't have one, but in the links above from Ettiene you can look at the open version with all the RED wires between top and bottom shell.
Note the bottom shell has two "pegs" on each end of the copper traces. Those pegs fit to the wholes in the bottom of the bezel/spacer in the image with the damaged ZEBRA.
The holes in the top-shell fits with the pegs on the bezel/spacer.

The whole thing is kept located and fixed together when you mount top and bottom half with the screws keeping it all together.

Hope this helps
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06-08-2021, 05:21 PM (This post was last modified: 06-08-2021 05:48 PM by Etienne Victoria.)
Post: #10
RE: HP 71b repair advice - won't power on with batteries or on AC adaptor
Perfect explanation from KimH while I was fighting to embed the pictures in my answer :-)

So here are the pics with the holes and the pegs.

The pegs:

Location of the lower pegs

The holes (and the upper pegs):

"Zebra 71B"

The "zebra" is simply sandwiched between the two halves, kept in place by the holes/pegs and tightened with the T6 screws.

HTH

Etienne

Edit : I have apparently lost my already limited ability to embed pictures in my posts. Who moved my cheese ????!!!
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06-08-2021, 10:25 PM
Post: #11
RE: HP 71b repair advice - won't power on with batteries or on AC adaptor
(06-08-2021 05:21 PM)Etienne Victoria Wrote:  Who moved my cheese ????!!!

In case you haven't read the book.
https://www.amazon.com/Moved-Cheese-Spen...0743582853
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06-11-2021, 05:47 AM
Post: #12
RE: HP 71b repair advice - won't power on with batteries or on AC adaptor
Ok, I've opened up the worse looking of the 2 units (in case I broke anything) and the photos are below. It came apart quite easily. Even the rubber feet are still intact (but will need double sided tape).

https://www.dropbox.com/sh/ljsoop5ggt43l...ee7ea?dl=0

Thoughts?

Worth trying to repair by soldering wires?

The Zebra connector doesn't appear to want to move, is this just pulled off away from the board or do I lever each end?
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06-11-2021, 06:40 AM
Post: #13
RE: HP 71b repair advice - won't power on with batteries or on AC adaptor
(06-11-2021 05:47 AM)dmh Wrote:  Ok, I've opened up the worse looking of the 2 units (in case I broke anything) and the photos are below. It came apart quite easily. Even the rubber feet are still intact (but will need double sided tape).

https://www.dropbox.com/sh/ljsoop5ggt43l...ee7ea?dl=0

Thoughts?

Worth trying to repair by soldering wires?

The Zebra connector doesn't appear to want to move, is this just pulled off away from the board or do I lever each end?

Pretty much what I expected it would look like.

Some gentle application of vinegar to get rid of all the corrosion (watch out for possible bridging between traces and components, use a loupe).

The “flange” for the zebra is probably held by corrosion as well, again vinegar is you friend.

Then on to the soldering…

I have repaired at least a handful that way, none failed to work.

Tip: use two different colors of wire alternating, it helps avoiding mistakes in the sequence.
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06-11-2021, 03:35 PM
Post: #14
RE: HP 71b repair advice - won't power on with batteries or on AC adaptor
(06-11-2021 05:47 AM)dmh Wrote:  Ok, I've opened up the worse looking of the 2 units (in case I broke anything) and the photos are below. It came apart quite easily. Even the rubber feet are still intact (but will need double sided tape).

https://www.dropbox.com/sh/ljsoop5ggt43l...ee7ea?dl=0

Thoughts?

Worth trying to repair by soldering wires?

The Zebra connector doesn't appear to want to move, is this just pulled off away from the board or do I lever each end?

Another cost savings with regard to the plastic-backed 71's is rather than using heavy metal shielding, the inside of the case is sprayed with a silver-colored metallic coating.
In the photos it can be seen that this coating has been attacked by the corrosion and is flaking off.

The PCB's can easily be separated from the case halves after the two wires to the beeper have been desoldered. Remove as much of the flaking metallic coating as possible.

Also of interest, sometimes the corrosion turns the PCB solder joints black. These black solder joints are very difficult to desolder. I suspect the surface of the solder joints has been altered and raised the melting point. Any insight into what is going on would be appreciated.

Dave
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06-15-2021, 06:18 AM (This post was last modified: 06-15-2021 06:22 AM by dmh.)
Post: #15
RE: HP 71b repair advice - won't power on with batteries or on AC adaptor
(06-11-2021 03:35 PM)Dave Frederickson Wrote:  
(06-11-2021 05:47 AM)dmh Wrote:  Ok, I've opened up the worse looking of the 2 units (in case I broke anything) and the photos are below. It came apart quite easily. Even the rubber feet are still intact (but will need double sided tape).

https://www.dropbox.com/sh/ljsoop5ggt43l...ee7ea?dl=0

Thoughts?

Worth trying to repair by soldering wires?

The Zebra connector doesn't appear to want to move, is this just pulled off away from the board or do I lever each end?

Another cost savings with regard to the plastic-backed 71's is rather than using heavy metal shielding, the inside of the case is sprayed with a silver-colored metallic coating.
In the photos it can be seen that this coating has been attacked by the corrosion and is flaking off.

The PCB's can easily be separated from the case halves after the two wires to the beeper have been desoldered. Remove as much of the flaking metallic coating as possible.

Dave

I can't see how the PCB's can be easily separated. The top looks plastic riveted and the bottom, although it looks like it is just sitting on plastic posts, doesn't want to move at all. Are the Zebra posts part of the lower case and holding the PCB down? As mentioned, Zebra doesn't appear to want to move either.

Any further guidance you can provide?

Thanks
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06-15-2021, 08:58 AM
Post: #16
RE: HP 71b repair advice - won't power on with batteries or on AC adaptor
(06-11-2021 03:35 PM)Dave Frederickson Wrote:  
(06-11-2021 05:47 AM)dmh Wrote:  Ok, I've opened up the worse looking of the 2 units (in case I broke anything) and the photos are below. It came apart quite easily. Even the rubber feet are still intact (but will need double sided tape).

https://www.dropbox.com/sh/ljsoop5ggt43l...ee7ea?dl=0

Thoughts?

Worth trying to repair by soldering wires?

The Zebra connector doesn't appear to want to move, is this just pulled off away from the board or do I lever each end?

Another cost savings with regard to the plastic-backed 71's is rather than using heavy metal shielding, the inside of the case is sprayed with a silver-colored metallic coating.
In the photos it can be seen that this coating has been attacked by the corrosion and is flaking off.

The PCB's can easily be separated from the case halves after the two wires to the beeper have been desoldered. Remove as much of the flaking metallic coating as possible.

Also of interest, sometimes the corrosion turns the PCB solder joints black. These black solder joints are very difficult to desolder. I suspect the surface of the solder joints has been altered and raised the melting point. Any insight into what is going on would be appreciated.

Dave

Not sure, but there is a known issue in bare PCBs where the pads of boards sometimes turn black, and the leading suspect is lead oxide or a lead sulphur compound. Lead doesn't oxidize easily, at least not to a black state, so it is suspected that there is some atmospheric contaminant that is either causing this, or is a catalyst for this happening. In the case of these HP 71s, it may be happening due to leaked electrolyte from either capacitors or batteries, or possibly even out-gassing from the rubber strips. In this instance, the oxidation is not on the bare PCBs, but the actual solder joints.

The lead is in the solder coating (or was) of the PCBs, used to protect the undetlying copper from oxidizing, and to enhance solder-ability (!). As you stated, it makes soldering/de-soldering close to impossible. It is also very hard to physically remove without destroying the solder pad entirely.
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06-15-2021, 02:36 PM
Post: #17
RE: HP 71b repair advice - won't power on with batteries or on AC adaptor
(06-15-2021 06:18 AM)dmh Wrote:  
(06-11-2021 03:35 PM)Dave Frederickson Wrote:  Another cost savings with regard to the plastic-backed 71's is rather than using heavy metal shielding, the inside of the case is sprayed with a silver-colored metallic coating.
In the photos it can be seen that this coating has been attacked by the corrosion and is flaking off.

The PCB's can easily be separated from the case halves after the two wires to the beeper have been desoldered. Remove as much of the flaking metallic coating as possible.

Dave

I can't see how the PCB's can be easily separated. The top looks plastic riveted and the bottom, although it looks like it is just sitting on plastic posts, doesn't want to move at all. Are the Zebra posts part of the lower case and holding the PCB down? As mentioned, Zebra doesn't appear to want to move either.

Any further guidance you can provide?

Thanks

That is a hard one without having the PCBs in front of me.

The "Top" PCB with the Display/KBD is what it is - risky to mess with and most likely not the cause of a malfunction unless the connectors to the LCD inside the Welded construct OR the KBD (an issue I for sure have seen) has been attacked by some chemical/fume. This could be tested with a good "Bottom", but that is not available to you.

The "bottom" PCB - once the Flange holding the Zebra is out - can be gently pulled out of the front Module ports - lifting the PCB part up-away-and-out from the ports ever so slightly. Again this is hard to judge unless having the possibility to handle the PCB. Force is not required for this.

The story about the Solder Joints going "black and hard" I have not experienced with a 71B, but I have with other products, it simply won't budge without destroying whatever it is soldered onto.
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06-15-2021, 02:46 PM
Post: #18
RE: HP 71b repair advice - won't power on with batteries or on AC adaptor
Sorry, the top PCB is heat staked to the case half and isn't easily removed. On the lower board the AC connector slides out, the battery contacts slide off, desolder the speaker, and the board should slide out. I don't think there are any screws but look around.

@Kostas Kritsilas
The black solder connections I've observed occur when the batteries leak.

Dave
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07-10-2021, 03:52 AM
Post: #19
RE: HP 71b repair advice - won't power on with batteries or on AC adaptor
Can I bathe the bottom board in vinegar once I get it out?

Has the AC socket still connected and wire to speaker.

If it’s safe and others have done then it’s quickest way to clean.

I’ve done Woodstock boards without an issue.

Has anyone done 71b boards?
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07-13-2021, 01:55 AM (This post was last modified: 07-13-2021 01:56 AM by dmh.)
Post: #20
RE: HP 71b repair advice - won't power on with batteries or on AC adaptor
(06-11-2021 06:40 AM)KimH Wrote:  
(06-11-2021 05:47 AM)dmh Wrote:  Ok, I've opened up the worse looking of the 2 units (in case I broke anything) and the photos are below. It came apart quite easily. Even the rubber feet are still intact (but will need double sided tape).

https://www.dropbox.com/sh/ljsoop5ggt43l...ee7ea?dl=0

Thoughts?

Worth trying to repair by soldering wires?

The Zebra connector doesn't appear to want to move, is this just pulled off away from the board or do I lever each end?


Pretty much what I expected it would look like.

Some gentle application of vinegar to get rid of all the corrosion (watch out for possible bridging between traces and components, use a loupe).

The “flange” for the zebra is probably held by corrosion as well, again vinegar is you friend.

Then on to the soldering…

I have repaired at least a handful that way, none failed to work.

Tip: use two different colors of wire alternating, it helps avoiding mistakes in the sequence.

Hi KimH,

So I opened my other dead 71b and it is very clean with only slight damage to the zebra and barely any corrosion and have soldered the 2 halves together with wire wrap wire but still no go.

Do you have any other suggestions / advice?

Thanks
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