uniden pc 66 XL no power

[Handy Andy]

Er, did you check the R84 power supply issue?

Channel Display power is thru Q18. So check it's feed...39 ohm 2W - and the Audio Amp branch.



Channels are thru front panel BRT/DIM switch

Hope this helps!
Regards!
:+> Andy <+:

 

[kaos513]

R84 reads 8volts on both sides

 

[Handy Andy]

Last hope - CB / PA switch - condition ok?

Long shot, does the radio receive? Like hit the Channel 9 switch, and find another radio to key up next to it on channel 9 a go - NO go situation. YES for RX (hurray)- then the display problem may be a voltage fed line broken - that problem lies in one of two places, the main PCB or with the Rotary BCD switch PCB to display board..

No display may indicate broken 90 degree Piggy board work, Use your DVM to see if you get continuity from the output of TR18 onto the Channel display board - it's a bit of finagling but the trace from the main PCB, goes up into the ribbon header into the channel selector - PASSES the selector and goes to be the COMMON ANODE feed to the display.



We may have fixed the display - but we still have a potentially dead PLL - Shoot..

Else...we rushed to help - provided quite possibly the first ever total repair work of a PC66 XL ever on the net - and the patient dies at the hospital - even after an attempted transplant...

Guess that, by indications - you're PLL has failed then too....but then you'll need to verify the D13 Zener, it will need repair. first. Something spiked this section - 8 volts now regulated down to 5 so proceed with caution.

You should get 7~9V on one side, with 5V only on the other. So the PLL may have failed. Otherwise you can check TP 2 - but if the PLL is not working - you don't get RX on channels - the speaker died - to let the operator know there's something wrong.

This may be as far as we can go unless you can swap in another PLL...

Regards!
:+> Andy +:

 

[kaos513]

there is power going to the channel 9 switch and also through the channel selector.

 

[kaos513]

will do more testing later on the pll

 

[Handy Andy]

Remember - the PLL has already a regulated 5 volt supply thru D13 - shown earlier. So if it's 8 volts, it means the regulator has stopped working.

The PLL would have taken current even at 8 volts. So with it NOT dropping any power across R84, indicates PLL or VCO behind it, is not consuming any current - period - possibly DOA - plus a lot of other issues.

So with you mentioning the negative voltage readings, I had to post what I usually see - to you.

For it (lack of voltage drop) - tells me that reversed leads inside the radio killed this - the PLL is only the start of this - the Zener was/would be forward biased in this reverse condition and would have popped like a fuse to the draw - it's only 1 watt but the parts behind and ahead in the circuit it powers are not necessarily protected from reverse biasing like that done at the power input.

And did you get any "funfetti" from blown electrolytics? If they're spiked in reverse, they blow, if not bulge due to the gassing...you should check for it anyways, because if this was handed to you - it may have been someone else's "baby" they threw out with the bathwater...so shorts may still exist.

Reversed leads? And the D17 polarity diode gone? nothing to keep it from getting cooked - at whatever voltage that was run in reverse (albeit forward inrush current) thru it. Knowing what I see normally - truck drivers and their floating ground between two batteries for only moment - in my own experiences was what spiked radios' like this with 24 volts - believe me - it kills them ... sad...

If you can restore it fantastic. I am not able to right at this moment.

:+> Andy <+:

 

[kaos513]

negative porlarity went away when i replaced the positive torroid wire

 

[Handy Andy]

But...R84 8V both sides...sigh...D13 - you said was ok, it should be working and giving/setting 5.0 volts to the PLL and all other support including Xtal 10.240 osc Q15 and associated. Which in itself - would show a current draw in use across R84 - so if the "Bead blew" and working - well, you have a lot more to work on, looks like D13 is on permanent vacation. ...

Add more to help...



Do you or did you not - perform a continuity check from R84 to Pin 1 of the PLL and was C104 - it's power filter - you said was ok? Hmmm...ok I await to see...


:+> Andy <+:

EDIT: Updated Graphic to show NOR (Normal Operation / Channel 9) CH 9 HEADER...NOR side highlited with Arrow

 

[kaos513]

i took the bead out and put a piece of red hook up wire on the positive side of power connector, thats how i got the radio to power up, as for r84 and pin 1 on the pll will be testing it soon and report back .

 

[kaos513]

r84 to pin 1 of the pll has continuity,also when radio is on i get my 5volts on pin 1 of the pll

 

[Handy Andy]

Just no display?

Status of TP2 - L15, the wax-covered - adjust this can for 3.5V (up to 4V) if you're on 40 - if you can get it there. Otherwise, you can try and see about "rotating the BCD" to see the steps, once you get to 40 - TP2 is at it's highest, then "dips" down to about 2.65~2.85 thereabouts for Channel 1 then "creeps back up" as you rotate the BCD.

This helps me when I'm dealing with bad segmented (broken display) LED's and I am locating the extremes Channel 1 and 40.

It can also help when "dialing blind" to tune RX to both ends and the health of the BCD "wafers'".

:+> Andy <+:

 

[kaos513]

Its Alive! bad channel 9 switch repair completed

 

[Handy Andy]

Quick - put "fixed" in the message header somewhere before it (radio) changes it's mind!

Congrats!

:+> Andy <+:

 

[kaos513]

Thank you andy and others for helping me oit.

 

[Handy Andy]

Do I need to edit the "gloom and Doom" or should I leave it in there for emphasis...?