My cobra 2000 gtl

[red97k1500]

Red97,

when searching out bad parts remember that any semiconductor is automatically higher on your list than any passive component like a resistor or a capacitor.

it is MUCH more likely that a blown transistor or IC took out a passive than it is that a bad passive took out a transistor or IC.
yes, it happens, but semiconductors are just much more fragile devices.

so, when you find yourself narrowed down to a certain circuit or section, check the voltages of the associated transistors first before trying to measure the values of resistors and caps.
of course having good service information is key here so you'll know what "right" is.

also, when re-capping that frequency counter box, BE CAREFUL!!!

i can't stress enough just how easy it is to mess up those traces.
you may already know this, but that board is double sided and plated through, which means you can't just use solder wick. you'll need an actual desoldering iron in order to get the caps out.
if you don't get ALL the solder off of the leads, you run a good chance of pulling the sleeve out with the cap.
then you'll have to solder both top and bottom of the board to the lead to make sure the circuit works.
yes, you can keep the trace heated and pull the cap out like that, but it takes a lot of patience and maybe some good luck.
LC

Thanks for the advice about soldering on the counter. Sometimes I try to subscribe to the if it ain’t broke don’t fix it mentality, or is it if it ain’t broke fix it till it is?

But I think the counter really does need to be recapped, I want this thing to last a long time. And I remember reading somewhere that damaging the counter is a real possibility. I plan on using my radio shack desoldering iron with the solder sucker bulb on it. Also I will probably do this outside on the driveway, because I plan on using plenty of liquid flux while desoldering, in order to melt the old solder faster/ more completely.
With a little luck, I think I will be able to get it done with out damaging the board, or lifting any of those little eyelet things out since it’s double sided.

 

[nomadradio]

We found that what minimizes stress to the foil on the pc board is to first 'walk" an electrolytic cap's two leads with the soldering iron. Heat one pad, tipping the cap to pull that one out of the hole, then the other one. This leaves two holes filled with solder. The internal surface inside each hole has a metal sleeve called a "plate through". It serves to connect the foil on the top side of that hole to the foil on the solder side. Solder will stick to this metal sleeve.

After the cap's two leads are pulled out this way, the only heat needed is to suck the solder from the empty hole. Tends to take less heat than trying to remove all the solder that sticks to the component leads if you simply apply the sucker to the pad with the capacitor's lead wires still in it.

The less total heat exposure to a solder pad, the less chance of damaging it.

At least one capacitor has only a round "doughnut" pad on the solder side. The ground foil is on the top side. The doughnut tends to just float away from the heat. Laying the lead wire of the cap's ground side over to reach a nearby ground on the solder side will take care of this problem.

73

 

[loosecannon]

We found that what minimizes stress to the foil on the pc board is to first 'walk" an electrolytic cap's two leads with the soldering iron. Heat one pad, tipping the cap to pull that one out of the hole, then the other one. This leaves two holes filled with solder. The internal surface inside each hole has a metal sleeve called a "plate through". It serves to connect the foil on the top side of that hole to the foil on the solder side. Solder will stick to this metal sleeve.

After the cap's two leads are pulled out this way, the only heat needed is to suck the solder from the empty hole. Tends to take less heat than trying to remove all the solder that sticks to the component leads if you simply apply the sucker to the pad with the capacitor's lead wires still in it.

The less total heat exposure to a solder pad, the less chance of damaging it.

At least one capacitor has only a round "doughnut" pad on the solder side. The ground foil is on the top side. The doughnut tends to just float away from the heat. Laying the lead wire of the cap's ground side over to reach a nearby ground on the solder side will take care of this problem.

73

LOL nomad you are speaking my experience with these things pretty much exactly.

I fully agree that leaning the cap to one side to get the lead out, then heating the other lead and just pulling straight up on the cap is a great way to do it.

of course there will be times when you can't lean it due to component density, but for the most part this is a safer and faster method than trying to completely remove all the solder from the trace.

just to add to the words of caution when doing this type of solder work, make doubly sure that when you lean the cap over to get that first lead out of the hole, that you get it ALL THE WAY OUT.

if you don't, the tendency is to go for the other hole, and lean the cap the other direction, which will cause the first lead to try to push back into its hole.
if the solder in that lead is not all the way solidified yet, which it probably wouldn't be, it can push the foil trace right up off the board.
ask me how i know...

i tend to use a dental pick, heat the trace, bend the lead vertical with the pick, then either go for the desoldering iron, or bend the cap and pull the lead out that way.

yes that counter does need to be re-capped, and it needs it more than the rest of the radio due to the heat in that box.

i will say that investing in a real desoldering station is a life changing experience when you do this stuff often.
once you get one you can't go back!
LC

 

[guitar_199]

THAT is NO LIE right there!!!!!

i will say that investing in a real desoldering station is a life changing experience when you do this stuff often.
once you get one you can't go back!
LC

 

[red97k1500]

No matter what computer or phone I use, or from where. when I try to login to the website I get a security certificate error, security certificate has expired, just curious if anyone else is experiencing this problem?

I made some progress on it. tr34 was indeed bad, it tested bad using a digital multimeter. so I swapped it out and now the radio tx normally. I even got some radio checks from locals and they said the radio sounds great. so now that problem is fixed.

Now I need to find a factory display for the freq counter, if anybody has one or knows where I can buy one let me know.

I got the s/rf meter unstuck using the methods described in the mikes radio repair video.
I thought I got the the modulation meter unstuck, but when I hook it back up. and then I key the mic, with the switch in the mod position the needle on the meter swings backwards a lil bit instead of forwards, any ideas on the this? I went ahead and ordered a new modulation meter, just because its in worse shape than the s/rf meter, but also hoping it would fix my problem.

 

[Van Lifeson]

Sweet! always wanted one, haven’t gotten one yet.

 

[red97k1500]

Small update, the cap kits I ordered from Klondike mike came in the mail the other day, so I will get started on that when I get some spare time.

Does any one know any common faults as to why the modulation/swr meter doesn’t work.
I put a brand new one in it and it didn’t fix it.
I put red leds in the meter lights since the wheat lamps were burned out.

 

[357magnum]

I know one thing for sure ... NO Hammer that size ( or any size for that matter ) is getting Near my 2K !

 

[red97k1500]

Lol I’m trying to remember what I was using the hammer and punch for now,but it was not on a radio. I need to put them back in my tool box.

 

[Handy Andy]

SWR/CAL/MOD switch?

Make sure that was not used for the PLL extra channel jumper.

The SWR board has two wires to that switch in the "deck" of your control panel - a third one comes off the "AM Regulator" line close to the Final - that line uses a pot VR7 - as for the MOD trim for meter.

You normally should not have damaged meters - the coil should still be good.

See below...


MOD meter uses SWR/CAL but when "switched into MOD", the MOD portion only works in TX mode where TX bias is being sent to Driver and Final. TR40 acts as a simple switch to GROUND the SWR/CAL/MOD meter only when in TX mode and when the Switch is in MOD - Refer to the switch diagram above for details...

If you get SWR/CAL and can use the SWR CAL pot on the main console - you have part of the wiring, if nothing works, then suspect that they used the DPDT switch to do channel mods...

 

[red97k1500]

Thanks Andy. I will look into all of it, I will trace some of the wires going from the switch just to make sure nothing funky was done with any of the wiring. And I will test tr40. I can’t find any evidence of channel mods ever being done to this radio, it does not have an mb8719. And all the soldering in the pll section appears factory.

 

[Handy Andy]

WHEW, that's good. But there are those parts that MONITOR the AM Regulator line the goes to the Driver and Final.

TR40 - a simple NPN, powers that SWR/CAL/MOD side of the meter.

For if it were to quit, which is possible, you may want to check the parts in that area

• - the caps that are placed on the MOD line to gat the audio side of that Audio BIAS
• - can fail shorted and yes, it can blow the meter - so it's possible - but I've not seen it happen directly.
• - I have seen people "jumper" the final and lose the MOD meter but still have SWR / CAL
• - it's because they pushed straight DC into the Final and so therefore, it kills the MOD side of the meter even though you're not on SSB
• - remember it's by location of that tap, that if they jumper the Final to...Yes, it does, the MOD will disappear at all times.

So if they jumpered the Final - remember that 220 ohm resistor on the OEM 1419 AM Regulator - it was for the purpose of reducing the load on that TR41/TR42 pairing and extend it's life. If they've kept everything stock, it is my hope then the SWR/MOD meter is a victim of age and bad caps...

IF mods were done to the AM Regulator section - this will affect how that SWR/CAL/MOD meter will operate.

Now you say it looks more stock than if anyone's worked on it, ok - then to lose that SWR/CAL/MOD meter tells me - you will need a re-cap then too.

Check those parts - for if the parts listed in the previous graphic are bad, the MOD line goes dead - but if the SWR CAL side of the meter has any damages like cracked parts or otherwise needs work - the whole mess shuts down.

Best to Check TR40 and then look for and repair anything looking suspicious in the SWR bridge area - once that is done, you prolly' find your SWR meter is back. And you may not have needed to replace that side of the dual meter element - but it's always nice to have a spare...

I did that graphic and I didn't put in the Meter Movement schematically, just remember the wires are going to the meter off that harness. As I get more time I'll do up the graphic with the meter in line so you don't have to "guess" - but the lines are for routing of the switch to help you more than the meter wires - they're part of the mess but I did not want to add more in case you did find trouble down the road.

 

[red97k1500]

You da man Andy! I changed tr40 and the swr and modulation function both work now.
Now I just need to recap the whole entire radio, which to be honest im not really looking forward to, but its the next thing that needs to be done.

 

[Handy Andy]

Final Revision of SWR/CAL/MOD reduced schematic...

​

You're welcome...Had fun with learning how to re-draw that...

Be sure to Grab a Cup of Coffee and a Doughnut and you're more than welcome to mingle with the crowd here and not have to worry about communicationable diseases like COVid-19 or even a headache, which are up to you if you really wanted to have them.

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[guitar_199]