Digital Clock

[wythet]

Hi folks,

Martin G kindly gave me a shifter plate with a hole for the digital clock (my '82 car didn't have a clock originally and I'm quite keen to put an original in). Obviously the clock doesn't work. I'm going to attempt a repair (transistor on the edge of the board is the most common issue apparently, which powers the illumination behind the LCD segments).

Just in case, would anyone have a working spare or know of where I might be able to obtain one?

Thanks!

Thomas.

[Rich H]

Hi Thomas

These are fully repairable.

The only thing that is terminal is if the display get cracked, easy to identify because the silvering at one end of the display turns white. In which case they should be saved for donor parts for other clocks!

Be very careful when removing/ refitting the plastic bezel, the 'bulb' at the end of the display has a little cut out where it sits - it's easy to shatter the bulb if not correctly seated.

[wythet]

Excellent, thanks!

I assume the transistor is at fault then. Any idea as to the spec of said transistor?

Thanks again,

Thomas.

[stunned_monkey]

It'll probably be a bad solder join on that transistor, not the transistor itself

[Rich H]

Quote:It'll probably be a bad solder join on that transistor, not the transistor itself

Agreed. Most probably, or bad solder around the diodes and resistors in that corner. All the ones I have seen have failed because an extremely thin power supply track has been corroded away due to moisture (drink spill)

Quote:I assume the transistor is at fault then. Any idea as to the spec of said transistor?

Can't remember the spec of the transistor off the top of my head, it's a BC something-or-other (BC327 springs to mind) if you PM the number on it and I'll sort you out

[Mrdashbo]

i recentley (after reading this post took out my clock to see if it can be fixed. it has a white dot in one corner of the display.

any ideas
Mike

[Rich H]

The silvering goes white on the inside of the glass.

Has the glass bulb been broken off the display at the end? Are there any cracks in the glass?

If the display has been broken, then it's u/s but can still be used for parts

[Rissy]

...After nearly 3 years of owning LEX, combined with the clock always bugging me being stuck constantly showing "12:00" and nothing else, no flashing, or dimming or anything, and then after talking to Rich H at the weekend, I finally got up the guts of removing my clock from my centre console for a look see.

Turned out my clock was ok, apart from the fact that it had originally been soldered by a blind, armless monkey in 1980 at manufacture.

De-soldered all the major, horrible looking, joints, cleaned up the HRS and MINS advance contacts after disassembly, and then cleaned up the board, and re-soldered all the de-soldered joints, and retested. Hey presto! working clock! All original functionality returned. Very chuffed!

Needless to say, it was a real careful time, making sure not to break the little glass nipple for the vacuum display etc.

I put the fault down to a combination of dry joints, and also suspected shorting out on the board. Some of the soldered joints were so badly done, that some contacts which are supposed to be isolated from one another, looked as though they were shorting out, although the gap (if any) was SO small, that they MAY have been ok, but now, their definitely ok.

[Chris Williams]

Thats great, I must say Rich repaired mine for me (and a good job he made too) it's nice to get something so little but so on show working properly!

Chris

[Nick H]

Hi Rissy,
Glad you sorted the clock. As I said at the weekend, it's a very satisfying repair. 8)
As Rich said more often than not it is a dry joint that causes the clock to fail.

Nick

[Rissy]

...I spoke too soon.

It's stuck again. Now showing "10:28". Static.

What is the most likely culprit for this? I hear some people mention a transistor, but there are two grey ones on the board.

Anyone know the details? ...if this is indeed the reason. I'm wondering if it was just the heat from the soldering iron last night which "loosened it off", only to return to what it was before, once cooled down again....?

[Nick H]

Sounds like a joint. If it worked while it was warm..

Here is link to some clock info. Replacing the guts with modern components.
http://delorean2109.blogspot.co.uk/

Regards
Nick

[Rissy]

Nick H Wrote:Sounds like a joint. If it worked while it was warm..

Here is link to some clock info. Replacing the guts with modern components.
http://delorean2109.blogspot.co.uk/

Regards
Nick

Hey Nick,

Yeah, I've seen this already. Very interesting.

I've once again, taken the clock out of the car and have started disassembling it carefully again. This time, I'm going to be even more thorough. I stopped last night after testing the resistors and the diodes and de-soldering EVERY SINGLE joint on the board. Tonight, I'll test the transistors to make sure they are working too (I'm not sure what to replace them with if they are not!?).

The only other thing then, is the chip, and the quartz crystal. Without making another circuit for the job, I can't test the crystal, and the chip, well, I think we both know there's not much can be done about the chip.

I'm hoping it is just a continuing problematic dry joint, and this is why I de constructed the board, by removing as much of the old solder as possible, this time replacing it with nice new modern and lead-free solder. As you say, it's strange how it all worked, for a time, potentially still feeling the affects from the heat of the iron. I'm very conscious that the soldering iron itself, with enough exposure, can damage the transistors, and possibly even the chip. I'm not sure if it's at all possible for a transistor to work fine for a bit, and then stop, and then be capable of working again in an on and off fashion, or whether it should simply work, then die, never to work again, which is more what i'd expect.....? if the contrary, then it still could be possible transistor issues the circuit is having. I don't know at this point if the transistors are being used as a switch, or an amplifier. I may never know with my knowledge of the board.

I'm handy to a certain degree with this stuff, but I definitely have my limits in capability for analysing circuits for diagnosing problems. I'll go as far as I can. Hopefully with some success.

[Rich H]

Like I said at Santa Pod, it's probably the crystal.

The transistor controls the display on/off so it won't be that.

The chips are expensive now, but can still be obtained

IIRC the crystal is bogo standard 32.768KHz and readily available...

Quote:with nice new modern and lead-free solder

It might be 'new' and 'modern' but it's certainly not 'nice' - Google 'tin whiskers' to see what I mean :roll:

[Rissy]

RichH Wrote:IIRC the crystal is bogo standard 32.768Hz and readily available...

Looking on the internet, there seems to be two different capacitance versions of 32.768kHz crystals. 12pF and 6pF. Which is it?

The only similar picture reference I can find, showing a crystal similar in appearance to the one on the board is this one:

http://forums.parallax.com/attachment.p ... 1309894236

On this link, the discussion seems to suggest that this model was not doing what the guy wanted, and was to replace it with a recommended replacement model:

http://www.parallax.com/StoreSearchResu ... fault.aspx

This one, is a 6pF. Does that give us any clue to the one in our clocks being 6pF and not 12pF?

It's pretty difficult to get underneath the display. Even with the soldered joints all de-soldered, it's hanging on there tight, meaning i'd have to be able to de-solder with the iron, on 36 points all at once in order to free up the display without risk of stressing it out, potentially causing a fracture!

Have you ever had a display off? Can you "wangle" it off bit by bit, by heating and reheating all the way round a bit at a time?