Uniden Washington dead transmit and receive.

[nomadradio]

When someone posts that his radio has no receive, or no transmit it's easy to assume that there is just one fault behind this failure.

When a radio has no transmit AND no receive, this points to a fault in a circuit shared by both the radio's receiever and transmit circuits.

But sometimes it's NOT just one failure.

This 1995 Uniden Washington was totally deaf, and had no transmit power at all. A look at the green/red LED on the front shows red when the mike is keyed. This tells you that the PLL is not out of lock. A look with the 'scope at the output from the PLL showed that the signal level was incredibly weak. That will do it.

The output coil L14 from the PLL branches off feeding into the transmit mixer and the receiver mixer. A look with the 'scope showed a peak with the tuning slug DEAD EVEN with the rim of the hole in the top of the can. This is a clue that the capacitor inside that coil has died. The apparent peak at this "flush" position is not really a peak. Just looked like one. And the output level from L14 was still really weak. Sure, plucking L14 out and replacing it with a new one will fix this failure, but there is a more-economical hack. Replace the function of the failed internal capacitor with an external trimmer cap, soldered across the two pins of L14 where the internal cap is connected.

With the trimmer adjusted to take the place of the failed internal cap, the slug of L14 now showed a proper peak, about three turns of the slug below the rim of the hole in L14.
Just one problem. Still no receive and no transmit.

Long story short, I found FIVE more slug-tuned coils with this problem.
One at a time.

Once every slug in the radio exhibited a proper resonant peak on the tuning slug, it came completely back to life.

Just goes to show that sometimes it's not "just one" thing that has failed in a dead radio.
73

 

[OldTech03]

I just put a cobra 2k back in service that the owner sent elsewhere to be tuned, it came back tuned for NO Transmit no receiving and found essentially the same issues a hacked variable resistor and a receiver so far out of tune it threw me for a bit they tried to tune-it-up and turn it up! I have seen these hundreds of times come across the bench as I'm sure you have. And I still to this day don't understand the process of handing or sending a unit back that don't work and acting like it does?

73 as well

 

[sunbulls]

Problems like that will make a person lose their hair. Cap failure inside modern IF cans are usually the last thing one thinks about. One would think they would use a better quality cap in such a critical circuit nowadays. This type of repair is commonly done with early tube radio restoration. The silver mica caps inside those cans were prone to crack or break down with age. Fortunately, those cans are large enough to think about repairing internally. “Silver Mica Disease” inside IF cans and dried up electrolytes are leading issues when it comes to restoring old tube radios. It appears they’re trying to make history repeat itself.

 

[nomadradio]

This is where the calibrated eyeball can save the day. That "dead even flush with the rim" position of the small tuning slugs is something I have learned to look for up front, even before touching a single adjustment.

73

 

[kaos513]

I have a question why not just replace the cans with new ones?

 

[Low_Boy]

I know I have asked this before but can not find the answer. So if I was to keep some of the variable capacitors on hand what would be a good size or sizes to stock up on?

 

[sunbulls]

I have a question why not just replace the cans with new ones?

I know I have asked this before but can not find the answer. So if I was to keep some of the variable capacitors on hand what would be a good size or sizes to stock up on?

Myself, I would only apply an external variable as a conformation test. At any instance where I have concluded that the internal fixed capacitor is bad, I replace the can. I prefer to use the same correct combination of capacitance and inductance that the manufacture recommends. The only practical way to do that is direct replacement. Schematics rarely state the inside cap value in those cans. Also, in many cases a bad capacitor will still have some unknown lower value. When you place it in parallel with a variable to make up the difference, who’s to say that no further deterioration will occur. My fear is that it will degrade even more at some point. Removing the tiny cap inside is not a practical option. If you go that far, you might as well replace the entire can. As far as trimmers go, I mainly use yellow. Those are in the 2.5pF to 40pF range and will cover a wide range of uses.

 

[nomadradio]

Make no mistake, replacing a 'can' that has gone bad with a new part is the very-best solution.

Always.

But a repair decision like this is driven by what the customer wants.

The radio in the example belonged to a horse trader who intends to sell it. His incentive is to minimize the expense of making the radio sellable again.

The customer's objective drives the "fix or replace" question.

And if the only part you can find that matches the old one is a "junkyard" part from a junker radio, the "patch" solution looks better.

These small IF, RF transformers and coils all look the same, but there is a vast variety of internal specs. The replacement must match the failed part. No internal details of the windings or internal capacitors can be found, as a rule. Makes judging what you can or can't substitute tough to judge accurately.

Some of them are still available. Year by year, more of them become unavailable as a new-replacement part. If you just can't get the part, and your choice is to "patch" the failure with a trimmer cap or junk the radio, this fix looks pretty good.

73

 

[OldTech03]

Make no mistake, replacing a 'can' that has gone bad with a new part is the very best solution.

Always.

But a repair decision like this is driven by what the customer wants.

The radio in the example belonged to a horse trader who intends to sell it. His incentive is to minimize the expense of making the radio sellable again.

The customer's objective drives the "fix or replace" question.

And if the only part you can find that matches the old one is a "junkyard" part from a junker radio, the "patch" solution looks better.

These small IF, RF transformers, and coils all look the same, but there is a vast variety of internal specs. The replacement must match the failed part. No internal details of the windings or internal capacitors can be found, as a rule. Makes judging what you can or can't substitute tough to judge accurately.

Some of them are still available. Year by year, more of them become unavailable as a new replacement part. If you just can't get the part, and your choice is to "patch" the failure with a trimmer cap or junk the radio, this fix looks pretty good.

73

A-men Brother, At one time I had over 20K invested in parts and about 5K in parts provided by companies that set me up as warranty repair and would still not have the part I needed sometimes. Now I'm collecting old radios in hopes they may provide me with the part needed, but I will modify it or the circuit with any means needed to get it working as long as the customer is okay with it. Just the way it works these days.

73's again

 

[357]

that picture shows a cracked solder joint

 

[dozerman]

that picture shows a cracked solder joint

Right leg? Looks like rosin to me..

 

[nomadradio]

Yeah, reheated it after I saw the pic blown up like you see. Too lazy to shoot a prettier pic afterwards

Gets the idea across, just the same.

73

 

[357]

I have a 451 you can have if its the same board you can take the inductors off.
Also C66 has given me trouble in the past