Autohelm Personal Compass playing up with new batteries

YBW image server is busy, so have a look at these two pics

http://picasaweb.google.co.uk/johncook1/Compass?authkey=Gv1sRgCOmboryGlM7yhAE#

Because the lcd is screwed down, I assume it's on one of those clever rubber contacts. Brilliant for capillary action.

Having connected the batteries many time over the last few days, I can say that the display has never shown gobbledegook.

Playing with one cell only. Won't start. So I can't buy the bent -ve spring theory.

Playing with flat batteries at 4.4V. I just held the light leds until the V dropped enough, and the unit turns off. This is completely repeatable. The only variation is that if I wait until it goes blank, pressing the on button either causes the 0000 display or, very occasionally the lighting leds come on. Next push gets 000 startup.
 
4.5V on my old batteries, inserting them I get ooo TT BAT where 'o' is the top loop of an 8, T is a sideways T - a 3 without the top and bottom bars and BAT is the low battery indicator. And it's happy to sit like this without powering off.

BTW, 'number 7' was a busy fella as my board is also marked with a green 7 sticker...which I presume is inspector or assembler.

Swapping to new batteries set #2 or #3, each give 5.5V and the unit is lifeless.

Interesting that you can 'force' your unit to power down by running the lights yet I get nothing with 'new' batteries giving 5.5V. What voltage do you see on the board with your 'good' batteries?
 
Thinking about your comment over the LCD and rubber contacts, is your thought that the unit itself may be working but the LCD partially failing? Might the LCD be capable of being removed, cleaned and replaced?

Just tried my unit again with new batteries #3 (5.6V on the board) and got the ooo TT BAT display quickly (<1 second) followed by the all segments lit (as in normal startup) for again <1 second followed by blank screen.

Gently pressing around the LCD makes no difference. This doesn't disprove the LCD contact theory, just fails to prove it.

Ideas?
 
Some pics of a broken apart Personal Compass for anyone that might understand a PCB from sight...although the processor is covered by a sticker.

If you plan to dismantle your compass, note on the 'Inside front case' picture the 'pressure pins' that sit (are not held) behind the rubber buttons. Two of the pins are slightly displaced to help recognition...but the sit square on the centre of the button.
 
To tell the truth I'm quite suprprised at how quickly these little chappies recover. At the minute they are at 5.9V, but using the light function takes them down to 4.4 in about 30 seconds. An hour later they are, as above, at 5.9.

I suppose that my suspicion of the lcd contact is that this sort of behaviour is what you get when a computer's video card is loose. It is, after all, the really crucial bit of the whole unit, pc or compass. Don't matter what else happens, it's the displaying of that stuff that requires complex binary strings to 2d display cleverness.

And the reason that I first thought this is that you have described a 'movement' of the unit in most of your works/fails descriptions. Movement disturbing duff connection.

Having said that, those rather cheap brass rivets would also act as potentiometers if corroded.
 
No my unit 'go wonky' when sat quite still and left alone. Always has done.

I has wondered about the battery connector rivets...note too the little tab through the PCB to aid contact. I'd wondered about soldering them and to be honest, I have little to lose by trying this. However, I have been measuring off the PCB itself and not off the connectors in an attempt to gauge what was really getting to the board.
 
Agree that solder might help on the rivets, but there is a capacitor way to close to the +ve for even me to try that one. As you say, you're now measuring V from the pcb, and I've shown that more than 4.4V is sufficient. (So your contacts seem to be fine).

Your large silver capacitor looks rather dull? Mine's vv shiny? Other than that I can see no differences.

Heading for bed. Will try to dream up a solution!
 
Autohelm compass batteries.

I use quite a few of these batteries in my workshop and only a little while ago
I bought a new supply of 20 for what I thought at the time was a good price.
Caused all manor of problems and I suspect the whole batch was either
faulty or poor quality.
I bought some more at full price and had no problems.
If your two sets of replacements came from the same batch, it might be the answer
to your problems.
 
Sadly not. New set #1 came from Maplins so probably fresh stock, with an expiry of Mar 3013 but that well known brand of 'Golden Power'. This set (together) now show 3V!

Set #2 came from Sainsbury's and are Engergiser with an expiry date of Jul 2017 so I'd rate as 'good brand' and 'fresh'. These still give 5.5V.

Set #3 came from batteries4youdirecto.co.uk and are Maxell with an expiry/best before of Aug-2014. These also still give 5.5V. I'd put these in the 'good brand' and reasonably fresh camp.

I'd also wondered about a 10-pack I think of Panasonic...only £5-something and again good brand although as I didn't buy these I don't know the expiry. However...

boguing's tests seem to conclude that anything above 4.4V is good to drive the unit and I am seeing 5.5V on the PCB with both sets #2 and #3, so sadly, I donlt think it's batteries. This was my first thought, hence the numerous sets!
 
More disassembly madness

boguing, reading your note again I see you came to the conclusion 4.4V and upwards will power the unit and below the unit shuts down. This nicely ties in with my original battery set (Eveready) which give me 4.5V. This then suggests the unit would have been on the point of signalling low battery and so lends support to the idea the unit only wanted new batteries. Events since suggest otherwise, but anyway, your 4.4V figure is a very nice match with my old batteries. So, to my other news.

I decided to ask my ex-Brother-in-Law who is an electronics whizz and see if he thought it might be the LCD contacts. Just possibly the unit was running, but the display not displaying properly...just possibly... He explained about 'zebra strips' which are rubberised contact strips used to connect something like an LCD to a PCB and yes, they could be worth a clean. So remembering comments about condensation and capillary action, I thought I'd give it a go. I've attached some photos for anyone else daft enough to go this far and to generally add to the body of knowledge about these units. So...

The gray plastic unit that is screwed from the back is nothing but a retaining collar. So when you remove the 4 screws from the back of the PCB you lift off:

- First the grey plastic LCD retaining collar
- Next the LCD itself
- Finally a white reflector card and spacer

At each side of the LCD there are rubber edges that lift the LCD off the PCB and above the white reflector card. These are the zebra strips. On the PCB you'll see the output tracks from the processor splay out to either side of the LCD and tiny black surface contacts. The zebra strips sit on the black (I guess carbon) connector patches and with the pressure of the retaining collar, all make contact and (we hope!) work. You can see my unit in various degrees if disassembly to try and show what I'm talking about.

I cleaned my PCB contacts and zebra strips first with a tissue soaked in meths and gently rubbed both the PCB contacts and zebra strips and after that didn't work, with plain old photocopier paper (a tip from my ex-Brother-in-Law) which has just enough abrasiveness to clean the contacts without removing them completely!

Replacing all the pieces after both cleans; the tissue+meths and copier paper cleans, the unit worked briefly and then stopped...precisely as it has done before...and so my conclusion is I don't have a display problem. In doing all this I also snapped the fact the unit is powered by a Hitachi HD44795C22 CMOS 4-bit microprocessor - http://pdf1.alldatasheet.com/datasheet-pdf/view/129656/HITACHI/HD44795.html - not that knowing this really helps me :-(

Note on my LCD at least, there is a fleck in black edging of the LCD on the botton of the LCB. Note in the third picture this is shown toward the top of the unit. This is because the LCD has been turned over to show the zebra strips...so the flect goes to the bottom on reassembly with the zebra strip 'legs' down towards the PCB.

So what I now know is that:

- I have 5.5V to the PCB
- I have clean LCD contacts with no moisture under them
- The unit still behaves in the same way...you may get it to work for 2 mins, then it 'goes wonky' with silly displays and then shuts down and then usually plays dead

So I'm no further forward other than being a little nearer to believing the thing is just dead and ain't going to be revived, although for the life of me I can't see why it would just 'go bad' without good reason and I now have boguing's '4.4V finding' which nicely ties up with my original batteries, suggesting the unit may have died due to low battery and not because of some other reason while retaining plenty of power.
 
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A friend of mine had a problem with a Playstation. After a bit of Googling he found that there is a common failure involving dry joints on the pcb.

The cure is to take a heat gun at it.

I'm trying to get hold of him, so will ask how he got on.
 
My other half used to work temporarily,6months, at the Autohelm factory, and was responsible for checking all the lcd displays before they were assembled into compass units. She says that any of the displays that showed a fleck or mark in the display were binned, and not used. This possibly means that this is now the problem you have, and perhaps to be expected after such a long time. I showed her the photos of the compass dis-assembled and she recognised it, but could not help further.

ianat182
 
Heat gun?

My concern about the heat gun approach is that the components are surface mounted, so it's not the back of the board you'll warm to help the joints, but the face and the components will be subject to the same heat as the solder.

I have another theory. The board has a 32.768 Tuning Fork oscillator - http://www.supplierlist.com/product...0/Tuning_Fork_Crystal_Resonator_32768KHz.htm- and a 10V 100uF capacitor. I am wondering if the capacitor is leaking slightly given it's age. Hence the circuit works for a while and then the capacitor gets to the point where the circuit first plays up, then simply doesn't work and 'goes dead'. Leave it several hours, try again and it again works for a few minutes before failing. Successive attempts to use the unit go from 'daft' displays to dead unit in ever shorter periods at each attempt until the unit simply plays dead because by this time the capacitor issue has built up. This is precisely the behaviour I see, so I'm going to try a replacement capacitor. Hopefully the oscillator/clock will be okay as its solder points are more fiddly :-)

It seems Maplins have some in stock for £0.18 so here's hoping... :-)
 
OldHarry...is your 'bend the connectors' solution still working reliably? Just wondering.

Had my unit run for 14mins 50 secs today on timer only. Had been wondering if my problem was entirely related to use of the compass but as 14:50 the display 'went daft' then blank. But... nearly 15 mins is a whole lot more use that usually in trying the compass where the unit may work for 1-2 mins max before going through different forms of dying before giving no clue of life at all.
 
This is fast becoming a PBO scrapheap challenge. I just wish mine was broken so that we didn't have to have all the post production meetings over the final edit!

I did say that your capacitor looked a little dull compared with mine.

And I like your theory too.

Mine is now based on heat transfer. A dry (can mean any number of things) joint might become less reliable as it warms. I've also had them go the other way, cold bad, warm good.

The hot air gun was used on a pcb which was covered in stuff that I don't think I'd have dared use it on. But. It worked. Can't see that, as long as the lcd is off (along with it's housing) much would suffer, other than, perhaps, the film over the three switches.
 
Well without wishing to extend the scrapheap challenge it was my hope both that someone out there might have seen and solved this problem, although that sadly doesn't seem to be the case and that it might provide a resolution for others in the same position as me.

What does seem evident though is that my experiences aren't unique...others have reported the exact same problems on a battery change. So far the only resolution seems to be OldHarry and his battery spring bending. Sadly that doesn't seem to work for me :-(

Anyway to my theories...

The change in capacitor did nothing. Same 'work for a while then stop, leave for a few hours, then work again' behaviour. So the leaky capacitor theory is I think dead.

So too the heat theory. Chilling the board made no difference nor did attempts to provide localised cooling to components. This isn't too much of a surprise as with only 6v driving the circuit and what must be a tiny current, there wouldn't be a huge amount of heat that could build up...other than maybe *inside* one of the ICs

So having been away for a few weeks and the unit left to rest, reconnecting things and trying again today yielded:

- battery voltage of 5.5V
- everything working fine to start with...timer running...
- Now 1hr 20 later it's still running happily...but why? Is it just the 3 week rest?
 
Spoke to my X Box user pal the other day. He cured this known fault with a hot air gun at 300C a few months ago. It failed recently, and he's 'fixed it' again.

Has to be worth a shot? Just on the back of the pcb.
 
Sadly no master reset. It's a seal unit in its usual state and there not even anything like a reset on the board once you break it all open. But it's still working...which I don't like as if you've not found a fault you don't know the fault is cured. It all comes back to "trusting the volts".
 
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