Uniden Zachary T no tx or rx?

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zinger827
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Uniden Zachary T no tx or rx?

Postby zinger827 » Monday 11th Feb 2013, 8:16

Radio Make and Model: Uniden Zachary T
PCB Number: PC-407AD
PLL Number: 2816
Test gear available: vom/freq. counter
Symptoms: No tx or rx

What is working: The PA does work.

What has been tried: nothing yet.

Did it suddenly happen ?: Got it this way but looks clean untouched inside.
Anything else that may be of help?: I can faintly hear myself on the speaker like talkback when modulating.

lbcomms
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Re: Uniden Zachary T no tx or rx?

Postby lbcomms » Sunday 17th Feb 2013, 0:48

The most common problem with these 80's / 90's Unidens (except for the golden screwdriver syndrome) is the "10 volt blues".
There will be 15 to 30 light grey 10V electrolytic capacitors, these fail (start to conduct DC, something an electrolytic must not do) after 10 to 20 years.

Replacing ALL of them - a process known as "recapping" - is the only way to make these sets reliable.

Usual symptoms of bad caps: no TX/RX but PA works. Trying to transmit gives faint audio on the internal speaker.
Other caps cause different failures: no TX, no Tx audio, low or distorted Rx, or no / very dim channel display.

The radio will look perfect inside (i.e. nothing looks burned out).

Hope this helps...

zinger827
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Posts: 35
Joined: Saturday 5th Apr 2008, 4:16
Location: Maine

Re: Uniden Zachary T no tx or rx?

Postby zinger827 » Sunday 17th Feb 2013, 1:15

How could I test for a bad cap? Would I have to pull to test first? Thanks.

lbcomms
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Re: Uniden Zachary T no tx or rx?

Postby lbcomms » Sunday 17th Feb 2013, 16:44

zinger827 wrote:How could I test for a bad cap? Would I have to pull to test first? Thanks.


From an electronics and communication engineer with 16 years experience: you don't.

Replacing ALL of them is the only way to make these sets reliable.

If we get in any pre-2000 Uniden chassis for repair, we now insist on replacing all the 10V electros BEFORE doing any other repairs. If they don't agree they are quite welcome to take it elsewhere.

Reason: The set will not be reliable if this is not done, and when it invariably fails, it will be us (as in "you fixed this last week and it doesn't work again, you did a c**p repair" type complaint) that gets the bad reputation, not them. So as far as we are concerned, it's replace them all or please go away.

Search Ebay for uniden electrolytic capacitor kit for a new set of caps and more info on why you need to replace them.

Edit: These were the ones removed from an SSB version (President Grant) earlier. All were replaced before attempting any other repairs (three quarters of the time, replacing the caps was all the radio needed):

Image

And make sure you get them all. Missing just one could leave the radio in an unreliable state.

zinger827
Dead Key
Dead Key
Posts: 35
Joined: Saturday 5th Apr 2008, 4:16
Location: Maine

Re: Uniden Zachary T no tx or rx?

Postby zinger827 » Monday 18th Feb 2013, 0:20

Ok looks like have to get me a capacitor kit. Thanks.


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