Sunwatch question

[digibloke]

I've been looking at a circuit board from an apparently dead synchronar sunwatch recently and have found this at the back near the oscillator crystal...



I'm far from sure but this looks to me like a diode which has a chunk out of it and a broken connection to the crystal solder joint.

I'm just guessing but perhaps it could be there to stop current drain from the batteries to the solar panels at night which would mean that there is now a gap in the circuit. Does anyone have any idea what this component is and what I should be looking to replace it with (just on the very slim chance that this could be a fixer).

[rewolf]

Looks more like a resistor to me.
22 Mega-Ohms, 5% tolerance
It is soldered in parallel to the quartz (telling from the photo).
This is part of the oscillator circuit, not unusal.
When the resistor is missing, the oscillator might fail or work unreliably.

[retroleds]

Striped item is a resistor...the stripes tell you the resistance. This URL
http://www.micro-ohm.com/colorcode/rescolor.html will let you delve into this simply. BAck in the 70's if you took an electronics class(like in high school), you were expected to memorize this - well, at least long enough to pass the test.

[leddwatch]

Times have obviously changed a great deal, when I did my Electronics degree back in the late 70's we were taught the following horribly racist saying, which has always stayed with me:

''Black bast***s roger our young girls, but virgins go without''

black, brown, red, orange, yellow, green, blue, violet, grey, white

0123456789

[digibloke]

Thanks very much for the pointers. I've been searching for about an hour now for a 22 Mega-Ohms, 5% tolerance resistor and I'm not getting anywhere (except horribly lost).

Could anyone give me an idea as to where I'd get hold of one of these?

I very much doubt it will bring the module back to life, but I'd really like to give it a try just in case.

[rewolf]

22M is hard to get, usually 1M is the top end, sometimes 10M
You can also use 2x 10M in series. 15M will quite surely also work.
SMD resistors will also do. Sizes 0805 and 1206 are easily hand-solderable.
Don't mind the tolerance, anything from 1% to 10% is ok.

Next, thorough cleaning from soldering flux residuals around the oscillator circuit is also a good idea. Isopropanol works fine. My experience with low power 32kHz oscillators (not in vintage watches though) is that even tiny amounts of flux can stop an oscillator circuit.

[Synchroserious]

ReWolf, as expected is right both about the type and it,s purpose.18-22M resistors are used and sometimes altering the value can change the voltage at which the crystal begins to function,but not really that much.

Over the years modules were taken apart for many reasons and on this one it is obvious to me that when it was opened the router sheared the resistor. The employee soldered the resistor in place sticking straight up or tilted outward which causes it to protrude outward from the PCB edge.When this happens it can give you a hang up on getting the top to fall down smoothly.


This unit is obviously one of the dilapidated ones my brother sold.


Isopropyl BTW is what breaks down the Gel.Problem is DON'T allow ANY to get near the chip area and the display because on many of the mass(40-50 per day) produced MK III,s they have an exposed IC and wires,covered only by the gel and the alcohol breaks down the epoxy used to mount the LED,s.One way to get a dim digit if you wanted one.



Digibloke, can you show a shot of the whole area? Does it have any corrosion? It may have been in a box of scrap evidence for so long this would be quite possible.If you see green lines by the IC you might as well give up now on that one.

[Synchroserious]

ReWolf, as expected is right both about the type and it,s purpose.18-22M resistors are used and sometimes altering the value can change the voltage at which the crystal begins to function,but not really that much.

Over the years modules were taken apart for many reasons and on this one it is obvious to me that when it was opened the router sheared the resistor. The employee soldered the resistor in place sticking straight up or tilted outward which causes it to protrude outward from the PCB edge.When this happens it can give you a hang up on getting the top to fall down smoothly and of course getting sheared when opened.


This unit is obviously one of the dilapidated ones my brother sold.


Isopropyl BTW is what breaks down the Gel.Problem is DON'T allow ANY to get near the chip area and the display because on many of the mass(40-50 per day) produced MK III,s they have an exposed IC and wires,covered only by the gel and the alcohol breaks down the epoxy used to mount the LED,s.One way to get a dim digit if you wanted one.



Digibloke, can you show a shot of the whole area? Does it have any corrosion? It may have been in a box of scrap evidence for so long this would be quite possible.If you see green lines by the IC you might as well give up now on that one.

[rewolf]

Isopropyl BTW is what breaks down the Gel.Problem is DON'T allow ANY to get near the chip area and the display because on many of the mass(40-50 per day) produced MK III,s they have an exposed IC and wires,covered only by the gel and the alcohol breaks down the epoxy used to mount the LED,s.One way to get a dim digit if you wanted one.

Ok, then better don't use Isopropanol . We use it at work to remove solder flux from prototypes, because it's better than Ethanol ("normal alcohol") as it doesn't corrode aluminium. Both alcohols don't do any harm to the expoxy coating of modern ICs, but this means nothing for vintage items...

[digibloke]

Hi, thanks again for the help. I just ordered five "22M ohms 1/4 Watt Resistor - High-Carbon Film - 5% tolerance" from the States.

Fingers crossed this is what I need to replace the broken component.

The circuit board looks very clean. It's got the exposed IC but the gel is still intact (except from where I've taken it off to get access to that broken resistor). I don't know anything about the history of the watch. I bought it on ebay as none working and it had been opened. I presume by the previous owner.

Here's a poor mobile phone pic of the whole board. It's even slimier than it looks...

[rewolf]

Hi, thanks again for the help. I just ordered five "22M ohms 1/4 Watt Resistor - High-Carbon Film - 5% tolerance" from the States.
Fingers crossed this is what I need to replace the broken component.

It's a perfect replacement for the broken component - might be a bit bigger than the original, but there seems to be enough room in the watch.

[Synchroserious]

Looks clean and now the only thing left to replace is the Q.C.This is a Mk III from around 1978 with the classic larger reed switches.Be careful working on that resistor because like the photo hints, it really is resting on the glass reeds.Pressing down to hard on the PCB while installing the new resistor can crack them if they are not already.One thing I notice is the display is the type with a protective cover and it is safe to roll the gel right off the display.Just like rolling carpet if you will.I myself have no problem doing this with other type displays but can't guarantee others will.The assumption people make is that the display wire bonds are going to break from the gel gripping and pulling them off.However this is only true for the IC wire bonds because the display is epoxy coated after wire bonding.In this case it is not a concern because it has the protective shield but it is still not a good idea to let Rubbing/isopropyl alcohol seap in from the backside through the little holes in the display PCB.


One more tip.

Don,t be afraid to use a clump of gel to attract and remove the bulk of other gel.Gel itself clings and removes the bulk and then you go with atleast 70% rubbing alcohol for fine cleaning arround the area of the QC and resistor.Best to do this stroking the tiny brush in one direction ,away from
the chip.

Mk I and MK II modules have a more solid gel and the clinging thing is not necessary.


Thats all for now.