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Message |
    
Lonestarbandit
Member
Username: Lonestarbandit
Post Number: 77
Registered: 10-2006
| | Posted on Friday, April 20, 2007 - 3:26 pm: | 
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hey lon im tryin to help an elderly cb aquaintance he has a recently given to him cobra 2000 base but the clock stays set untill the radio is turned off during which it STILL remains correct. then when the radio is turned ON it defaults to 12:00 id like to help the guy out but all i can think is a capacitor is bad or does it have a battery backup for clock memory thats dead? |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 2501
Registered: 9-2004
| | Posted on Sunday, April 22, 2007 - 2:18 am: |
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no battery backup in the 2000gtl.
most likely a bad elec. or tantalum cap in the freq. counter module.
must be VERY careful when soldering and desoldering on this board as it is double sided and plated through, meaning that there is a small brass tube in each of the PC board holes that provides continuity from the bottom of the board to the top.
if any solder is left on the cap when desoldering and pulling it, the chances are great of pulling the brass tube out with it, and ruining the board.
must use a desoldering iron with a hollow tip and a suction mechanism built in.
red bulb from radio shack wont cut it.
braid wont work either.
there's about 10 elec.caps to replace and a few tantalums.
sorry i cant direct you towards which one it is.
you'll have to re-cap the whole thing.
this is considered somewhat of a difficult repair and is best left for a tech.
thats up to you.
best of luck,
matt
anyone wanting a "clean signal", just look to the left and build one of these!!!
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2600
Advanced Member
Username: 2600
Post Number: 590
Registered: 7-2002
| | Posted on Sunday, April 22, 2007 - 4:19 am: |
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Weird troubles with the counter display and/or the clock mostly boil down to one or more failing filter capacitors in the counter/clock module. It has 9 or 10, depending on the the production version. Heat tends to determine the life of those parts, and the inside of the counter shield is the hottest part of the radio's insides. Makes the small electrolytics in the counter module fail first. Most common symptom is phantom flickering digit segments that should be dark, but aren't.
There are also a handful of 10-Volt rated filters on the main radio board that will probably start to fail soon after the radio goes back into daily service. Since the temperature of the main circuit board runs a bit lower than the counter, they take longer to get senile and cause trouble. If the radio has had a long shelf visit, one or more of these "Ten-Volt Blues" caps will shut down the first few weeks of regular use. Might kill all mike audio, or all receiver audio. Another one will kill all transmit, AM and SSB both. And yet another one causes a squeal in the AM mike aduio, especially when the carrier power is turned down.
Best and only real solution to a clock or counter problem is to replace every electrolytic in the counter module. You'll need a desoldering iron with a heated tip. The printed circuit board in the counter is what's called a "double-sided plate-through" pc board. This means that a tiny metal sleeve lines every hole in the board. Getting the solder removed with braid or a teflon-tipped sucker will just cause you to overheat foil traces and make them lift. Worse, if you pull a lead wire out of a hole and it's still soldered to that metal sleeve inside the hole, this may remove an important circuit connection from foil on the top (component) side of the board to the foil on the lower (solder) side of that hole. If that tiny sleeve pulls out of the board still attached to a component's lead wire, a tiny wire jumper must then be slid into the hole with the new part's lead wire, and soldered to both top and bottom foil pads on that hole.
The sucker with the heated hollow tip will reduce the risk of this quite a bit. RatShack has sold one for years pretty cheap, stock number 64-2060.
Got a list of the counter-module caps here somewhere. Probably on the 1992 pre-internet computer.
73 |
Lonestarbandit
Member
Username: Lonestarbandit
Post Number: 78
Registered: 10-2006
| | Posted on Sunday, April 22, 2007 - 8:19 pm: |
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lovely. thanks tons for all the info while i do have the skill to do the repair this sounds very time consuming and i dont have the free time to do all of that for no fee lol. guess ill let him know what the problem is so he can find someone to do the work if it really is that important to him. again thanks for all the excellent information. |
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