Uniden 2830 help req

[flash22]

Have recently picked up a uniden 2830 and wondering if any one could help

The radio works fine on rx but there seems to be a fault on the tx side. I have tested both output transistors (in and out of circuit) and thay seem to be fine (2SC2166 and MRF477)

I dont know if it related but S/Swr meter doesnt work on tx but is fine on rx (apart from when you drop the key it goes to about s7 for split sec)

Any help would be most appreciated

 

[Rogerbird1]

Hello

Did I send you an email regarding this already?
If not Email me. Rogerbird @ netscape.net
(Remove spaces)
Or use the link on my webpage, http://Rogerbird.tripod.com

I am thinking its a shorted Cap or bad TX Switch transistor.

Roger

 

[flash22]

Hi rog yes I did send you a Email

No luck as of yet i'm afraid voltage on IC104 was fine the caps where a bit duff so I changed them as You suggested Q125 and Q136 were dead so thay where also changed

The radio just seems dead on tx and i wondering wether or not its worth throwing any more time/money at it.

 

[Rogerbird1]

Next step

Ok. the next step would be to check the Bias voltages.
That will help determine if the final or driver or Bias Diodes are bad

A bad final may be $$ to replace, but if its a Driver or other minor parts, I would say it is worth getting fixed.

Let me know If I can be of help.

Roger

 

[flash22]

Thanks again roger

This radio is driving me mad everthing seem to check out ok I have replaced the 2sc1622 as you say its only the final that can be at fault I am in the uk and the MRF477 is a hard part to source (most radio parts are hard to get hold of) as for cost the MRF477 is £36.95 ($68.00) so i think i will wait till another radio comes up or stick it on ebay as spares

 

[Rogerbird1]

troubleshooting steps.

Ok, Not knowing the steps you have taken, and the things you have found, here are some things to check...

You did not mention what the bias readings were, but you said you tested the finals in and out, so for now I will assume they are ok.

Check C119 (in front of the Final next to Vr112) I have seen those short out and even explode and cause final probs.


You stated Q125 ans Q136 were bad and replaced, they are the TX regulated voltage line (What sends the key-up sig to the transmitter) If they were both bad then that is where you should be looking in the key-up ckt.

Assuming you now have 8v tx voltage on Q125's emitter when transmitting.. This voltage is fed to the Bias pots, and the Pre-Driver Q134. You need to check the transmit voltages (in AM ) the Collector of Q134 should be about 4.3Volts (see http://www.cbtricks.com/~rogerbird/2510/2510_trans.htm )
the base of Q134 should be 2.2v.
The base of Q133 should switch to 2.2v on TX.
The base of Q132 should switch to 0.4v on TX.

If these are correct voltages, Check D101 and D102 (probably have to lift one side of each and diode check them, I have see a shorted D101 load down the TX output - these are the Receiver Rf attenuators.)

If any of these voltages are way off, you should inspect the associated caps and resistors for damage, Bias controls, Bias Diodes, supply resistors, coupling caps etc.

I just had a radio where the TX was severely loaded due to a lightning hit, the Finals were good, but several of the coupling caps to the Receiver and Meter ckt were shorted causing no output power.

You sound like you are close, so maybe just a few more checks and you are there..

Let me know how you make out,

Roger