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Uniden Pro 810e power supply question.

Discussion in 'General CB Services Discussion' started by Emperor, Jan 5, 2018.

  1. Emperor

    Emperor Member

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    Hello everyone,



    I'm a new guy here and this is my first post. Would someone who is familiar with the Uniden Pro 810e, kindly share their knowledge base and steer me in the right direction, regarding my problem.

    The transceiver has poor receive performance and weak (less than 1 watt) RF output. I checked the DC voltage of the built-in power supply and the voltage is 7 volts. It should be around 13.8 volts.

    My question is; What is the likely component(s) on the power supply (B801 PA-241AB) board that would be suspect? I purchased the rig new and in spite of my avatar, the unit has not been modified.

    Thank you for any help.
     

  2. Robb

    Robb Yup

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    http://www.cbtricks.com/radios/uniden/pro_810e/index.htm

    Test output voltage of the power xformer with a DMM for ~18vac. Be VERY, very careful since you are dealing with AC! Test it at the black rectifier block; two ends should read in AC about 18v; and the opposite two will read about 17vdc.

    The rectifier block should be marked with two "~" symbols for the AC in side; the other two are rectified DC out side.
    Be very careful; or pass on doing this.
    Best to test that DC voltage where the two wires from that rectifier block connect to the voltage regulation board - IMO.

    If that checks out OK; then move to the PA-241 voltage regulation board. Examine it for poor solder joints, failed electrolytic caps, and burned resistors for starters . The voltage regulator is mounted both to the side of the case and to that board. If you aren't seeing 13.8v on one of its pins to ground; then it is either at fault or the fault is still upstream from it . . .

    Service manual:
    http://www.cbtricks.com/radios/uniden/pro_810e/graphics/uniden_pro810e_sm.pdf
     
    #2 Robb, Jan 5, 2018
    Last edited: Jan 5, 2018
    338_MtRushmore likes this.
  3. Emperor

    Emperor Member

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    Thanks for your help, Robb. I'll be careful and check those areas tomorrow.
     
  4. Robb

    Robb Yup

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    Here is a schematic of the power supply circuit. There is also a 5.6v 1/2 watt zener diode (D801) and a few other parts that should be checked out as well. Never worked on this radio myself; so please keep us posted on your findings. Had a 510e mobile radio with the same radio chassis; but not the base version you have.

    supply sch.PNG
     
    #4 Robb, Jan 5, 2018
    Last edited: Jan 5, 2018
  5. Emperor

    Emperor Member

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    Thank you for the schematic, Robb.

    I'll check things over and report back. Thought it may be the radial lead 35v electrolytic, but it could be anything and need to check with a DMM. Will take it safe and slow...

    Thanks for your input.

    Doug
     
  6. 357

    357 Walkin' the dog

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    just make sure you unplug the radio when poking around.
    The power switch doesn't really turn off the power supply, just kind of puts it in standby.
    I fried one before and it sucked.

    there is and adjustment, maybe it needs to be worked back and forth to clean the connection.
    Seen that before
     
  7. Emperor

    Emperor Member

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    Thanks 357,

    Yes, I have been unplugging the unit before poking around. Capacitor C802, a 25 volt electrolytic, is showing an output of 8 volts. C804, is a 35 volt electrolytic and its output is 25 volts. Unfortunately, VR801 does not increase the 7 volt output voltage, unless it's opened fully. It will then show over 22 volts. There is no voltage from Q504, the voltage regulator. Still investigating, when my time schedule permits.

    I will post my findings when the unit is repaired...

    Doug
     
  8. Onelasttime

    Onelasttime Well-Known Member

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    That is kind of strange these supplies are super simple. Normally they are insanely easy to find the fault cap, diode or the transistor doing the regulation. Usually fairly straight forward.

    Usually if a radio is more than 12 years old and the power supply is wonky before I do much else new cap's, rectifier and transistor. If it is 16 years old or older I recap the entire radio before I even think about giving it an alignment.

    If a cheap consumer piece of gear has been sitting around for a long time and is also old you can be chasing your tail for a while if a few caps are close to being nonfunctional or way out of spec.

    That thing does not have that many devices in the power supply and all of them are dirt cheap to replace. You are looking at less than $5. Nothing is worse than old filter caps in the power supply area in terms of noise in the system.
     
  9. Emperor

    Emperor Member

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    Thanks for you insight, Onelasttime. I had recently ordered some electrolytic capacitors and we're awaiting their arrival. Hopefully, that does it. If not, it's back to the schematic that Robb had graciously supplied and looking at other possibilities. Perhaps, Q504, a diode or resistor... we'll see.

    -Doug
     
  10. Staybolt

    Staybolt Well-Known Member

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    Id just run it off of 12 volt. Most power supplies in radios suck anyways.
     
  11. nomadradio

    nomadradio Analog Retentive

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    People ask if we fix power supplies. I generally reply "Not often, but we do a lot of autopsies on them".

    Reason is the labor-intensive part of repairing them. If you don't test every part that COULD have been damaged during a breakdown, you'll miss one. Result of this is that it won't work, or work properly. This tends to make the price to repair an external power supply roughly equal to the replacement price, sometimes more. When the customer hears the estimated price to fix it, the estimate becomes an autopsy.

    Doesn't matter how many (or how few) parts are in a power supply. If they don't *ALL* work, it won't either.

    This rule applies to the one in the radio. If you have a way to check every zener diode, rectifier and transistor, you should be good to go. Any resistors that look dark or have faded color bands could have been damaged and need to be replaced.

    Nothing mysterious about power-supply repair. You just have to make sure that EVERY SINGLE part in the circuit is good.

    If they are, it will work.

    73
     
    Robb likes this.

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