So i got the like new cobra 138xlr radio today (ebay) and it is very nice, like new. Seller said it works perfectly and of course he lied, yaaayyy, scumbag. Anyway, the radio works 100% perfect except for lsb. In that mode it is completely dead. No transmit or receive. Usb and am are perfect. I have not looked around good inside yet. The mode switch is sealed and makes no noise when turned so it probably isn't that. Any clues or suggestions on where to look or what it could be?
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Cobra 138xlr dead on lsb only
- Thread starter groundwire
- Start date
It might be the 11MHZ crystal for lower side. Up by the PLL there are 3 crystals side by side. (X3, X4 and X6) X3 is upper side, X4 is lower side and X6 is AM. They should be in sockets. Try swapping X3 and X4 and see if lower side works and upper side quits. If so, you know the 11.2842 crystal is bad. Sometimes it's just oxidization and cleaning the socket/crystal pins with De-oxit will fix the problem.
Cool thanks, it is the xtal. Where can i find a 11.2842 xtal for sale? Searched online, nothing. None on ebay either
Cant find it on his site, which is very messy. I emailed him. We shall see. Kind of odd but the crystal i have, i flicked it hard with my finger like 6 times (why? Idk lol) and it is working fine now so far. Hahaha wtf? Im still gonna try and find a new or used one to buy
Shadetree Mechanic
Delaware Base Station 808
Maybe a cold or cracked solder joint or a cracked trace? I would reflow all the connections in the crystal area just because it's easy to do.
Edit:
I just re read your other posts. I assume the problem moved to usb when you swapped crystals?
Well, how deep do you want to find the quirk.
IF it were me, I'd just compare voltages to the other sections.
Although most would say "Xtal" !!! While that would work for most, only some of the time - and only if physical things were wrong - like that "Glue adhesive" etchant they put on back then.
Xtals can drift, and even fail, but no one bothers to check the regurgitated oscillator that the Xtal works with to put out something. A voltage check can reveal a drift of 1 to 2 volts of the load on the line can wreak havoc with the oscillator - they need pure DC, not a noisy power feed, they don't like jitters - or at least you won't like what they produce when they get those "jitters".
The other two work, might want to figure out the third using the others as the reference - it can help you later.
You said the "switch was sealed" means squat when it's this old. You still have the wiping action and lack of use issues plus the construction - let alone the "long term seating arrangement" of leaving a path in the carpet of the old homestead, shows up here on the switches too. (You did say you got it from "A Merchant That Identifies Itself as Electronic Stores")
Sealed switched does no good in high humidity and or left out in a Attic/Basement or mobile and not used often enough - worse than finding the old beast and saying "Hey - I wonder if this thing still works!" only to hook it up, apply power and Pop-pop - BANG - dead - "WTF - moment" and then opening it up you see it filled with funfetti from the Electrolytic caps that passed gas and woke up explosively.
Consider the Radios' age and be thankful that didn't happen - you just have a goofy oscillator.
IF it were me, I'd just compare voltages to the other sections.
Although most would say "Xtal" !!! While that would work for most, only some of the time - and only if physical things were wrong - like that "Glue adhesive" etchant they put on back then.
Xtals can drift, and even fail, but no one bothers to check the regurgitated oscillator that the Xtal works with to put out something. A voltage check can reveal a drift of 1 to 2 volts of the load on the line can wreak havoc with the oscillator - they need pure DC, not a noisy power feed, they don't like jitters - or at least you won't like what they produce when they get those "jitters".
The other two work, might want to figure out the third using the others as the reference - it can help you later.
You said the "switch was sealed" means squat when it's this old. You still have the wiping action and lack of use issues plus the construction - let alone the "long term seating arrangement" of leaving a path in the carpet of the old homestead, shows up here on the switches too. (You did say you got it from "A Merchant That Identifies Itself as Electronic Stores")
Sealed switched does no good in high humidity and or left out in a Attic/Basement or mobile and not used often enough - worse than finding the old beast and saying "Hey - I wonder if this thing still works!" only to hook it up, apply power and Pop-pop - BANG - dead - "WTF - moment" and then opening it up you see it filled with funfetti from the Electrolytic caps that passed gas and woke up explosively.
Consider the Radios' age and be thankful that didn't happen - you just have a goofy oscillator.
Yup. When i put the usb xtal in the lsb slot it works fine and usb dead with lsb xtal in its slot. So definitely the xtal. Its still working fine now after i flicked the lsb xtal a few times. Why idk? Still going to get a new one
If you can "flick" the crystal with your finger and get it to work, you might try heating the mounting pins ever so slightly with a soldering iron. This may damage the crystal, but it's toast anyway so give it a try.
Also, if you have a hard time locating a 11.2842 crystal, several Uniden CBs used an 11.2850 crystal which could be pulled down to .2842 during tune up. I saw several of these advertised after doing a Google search. Good luck.
- 399
Also, if you have a hard time locating a 11.2842 crystal, several Uniden CBs used an 11.2850 crystal which could be pulled down to .2842 during tune up. I saw several of these advertised after doing a Google search. Good luck.
- 399
http://nettyelectronics.com/crystals.html
Canadian site that has one listed. 2$ ? + $7 to ship it to USA in a padded mail envelope.
Canadian site that has one listed. 2$ ? + $7 to ship it to USA in a padded mail envelope.