06 Nov 2011, 03:50
Hi,
I have been collecting and working on 1940s to 1970s mechanical watches for a little while and being a child of the seventies have been after a LED watch for a while. Hard to come by in my price range though.... Plus I'm a little fussy.....
Anyhow, I managed to get a bargain on a lot including a Working Stainless Novus recently (this is the watch - http://www.ledwatches.net/photo-pages/novus6.htm). Unfortunately the Novus wasn't actually working when I received it but as I really like the case and want to get it going eventually I agreed a partial refund with the seller (who was really good about it) and so I've kept it.....
I've read through this and various other LED forums and this Digital Workbench area seemed like somewhere that I might pick up a few tips to help me along. So here I am....
The module is obviously a Nat Semi one (red dots / 29mm) and is in visibly good condition on opening. With new batteries there are some random static numbers (or not) when powered up. And the Set button does register occasionally by cycling through some rubbish. The command button does nowt. I did notice during the heiroglyphs that two of the dots - on different digits - were out. The pins on the buttons have impressed their brass contacts/tabs so the buttons have obviously been frustratedly hammered for a while.
So I'm going to order a new Xtal tomorrow and fit it on monday. I have removed the old one and its accompanying silicone strain relief. I did this with the PCB still in the black plastic chassis to guard the gubbins on the 'dial side'. And when I took the plastic chassis pieces off I'm so glad I did - no soft encapsulant. There was about a millimeter of lateral slip when I took the PCB out but I'm pretty sure I got it out without fouling any of the wirebonds on the chassis stand-offs.
The button issues seem to be down to some corrosion on the two button input tracks. The corrosion has grown either from water ingress at the command switch or nucleated on some leftover flux at the button tab soldering. On both tracks the corrosion has largely but not completely eaten the tracks to within about a milimeter of the wire bond point by the black coated IC. I managed to get all of the corroded track off the board with sharpened pegwood. A bit hairy with all of those naked wire bonds around.
I've cleaned up the rest of the tracks on the battery side but am doing as little as possible on the wire bond side. I think with some conductive epoxy I can reinstate all of the necessary tracking on monday when I do the new Xtal. I've also gently straightened out the button tabs - hopefully without critically fatiguing them.
So I have a couple of queries -
1/ What else might I try if I don't have basic operation after these simple repairs?
2/ From experience do you ever have issues with the Trimming Caps? I guess that if so the easiest fix might then just to drop it and fit an oscillator in place of the Xtal?
3/ The missing segments. So I've inspected all the wirebonds under limited magnification and they look OK. There doesn't seem to be a common address line to the two missing ones I saw so there's either multiple hard to see wirebond issues (quite possible with aging on these naked bonds...) or silicon problems. So I guess I could try and reinforce the apparently dead lines with some diluted silver loaded epoxy. I can't help thinking that with the naked wirebond nest and my limited equipment I will probably do more damage than good. So I think that eventually I will be looking for a new module because I do really like the case and want it to run properly as well.
4/ What batteries should this module take? It arrived fitted with dead sr44s. They're just a bit difficult to fit with the battery clamp/contacts on top - seem a bit high.Wrong batteries might raise the possibility of bowing stresses on the PCB. Ugh.
If it hadn't been free I'd probably be disgusted with this module. As it is it seems to have taken on the appealing charm of a destitute dog. For now at least.
Rgds,
Mark.
I have been collecting and working on 1940s to 1970s mechanical watches for a little while and being a child of the seventies have been after a LED watch for a while. Hard to come by in my price range though.... Plus I'm a little fussy.....
Anyhow, I managed to get a bargain on a lot including a Working Stainless Novus recently (this is the watch - http://www.ledwatches.net/photo-pages/novus6.htm). Unfortunately the Novus wasn't actually working when I received it but as I really like the case and want to get it going eventually I agreed a partial refund with the seller (who was really good about it) and so I've kept it.....
I've read through this and various other LED forums and this Digital Workbench area seemed like somewhere that I might pick up a few tips to help me along. So here I am....
The module is obviously a Nat Semi one (red dots / 29mm) and is in visibly good condition on opening. With new batteries there are some random static numbers (or not) when powered up. And the Set button does register occasionally by cycling through some rubbish. The command button does nowt. I did notice during the heiroglyphs that two of the dots - on different digits - were out. The pins on the buttons have impressed their brass contacts/tabs so the buttons have obviously been frustratedly hammered for a while.
So I'm going to order a new Xtal tomorrow and fit it on monday. I have removed the old one and its accompanying silicone strain relief. I did this with the PCB still in the black plastic chassis to guard the gubbins on the 'dial side'. And when I took the plastic chassis pieces off I'm so glad I did - no soft encapsulant. There was about a millimeter of lateral slip when I took the PCB out but I'm pretty sure I got it out without fouling any of the wirebonds on the chassis stand-offs.
The button issues seem to be down to some corrosion on the two button input tracks. The corrosion has grown either from water ingress at the command switch or nucleated on some leftover flux at the button tab soldering. On both tracks the corrosion has largely but not completely eaten the tracks to within about a milimeter of the wire bond point by the black coated IC. I managed to get all of the corroded track off the board with sharpened pegwood. A bit hairy with all of those naked wire bonds around.
I've cleaned up the rest of the tracks on the battery side but am doing as little as possible on the wire bond side. I think with some conductive epoxy I can reinstate all of the necessary tracking on monday when I do the new Xtal. I've also gently straightened out the button tabs - hopefully without critically fatiguing them.
So I have a couple of queries -
1/ What else might I try if I don't have basic operation after these simple repairs?
2/ From experience do you ever have issues with the Trimming Caps? I guess that if so the easiest fix might then just to drop it and fit an oscillator in place of the Xtal?
3/ The missing segments. So I've inspected all the wirebonds under limited magnification and they look OK. There doesn't seem to be a common address line to the two missing ones I saw so there's either multiple hard to see wirebond issues (quite possible with aging on these naked bonds...) or silicon problems. So I guess I could try and reinforce the apparently dead lines with some diluted silver loaded epoxy. I can't help thinking that with the naked wirebond nest and my limited equipment I will probably do more damage than good. So I think that eventually I will be looking for a new module because I do really like the case and want it to run properly as well.
4/ What batteries should this module take? It arrived fitted with dead sr44s. They're just a bit difficult to fit with the battery clamp/contacts on top - seem a bit high.Wrong batteries might raise the possibility of bowing stresses on the PCB. Ugh.
If it hadn't been free I'd probably be disgusted with this module. As it is it seems to have taken on the appealing charm of a destitute dog. For now at least.
Rgds,
Mark.
Yeah, the National Semi module is not to well armored against various damage, and looking throught the silicone over the wire-bonds of most of those is not very encouraging, since you might see the problem but have trouble getting to it - short of destroying everything else. You might get it orking, but when the damage is that extensive, you have to wonder how many fires you will have to put out before you have it under control. It's a very common module - you may just want to snag on in some hideous looking plain watch that is still working. And save that one for tinkering with.
![[img]http://img254.imageshack.us/img254/2752/novusmoduleside.jpg[/img]](http://imageshack.us/photo/my-images/254/novusmoduleside.jpg/){kind=link}
![[img]http://img510.imageshack.us/img510/3817/novusmoduletop.jpg[/img]](http://imageshack.us/photo/my-images/510/novusmoduletop.jpg/){kind=link}