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Overvoltage to Ubitx - now no receive

sumit basu
 

Hello,

My Ubitx ver 4 does not receive anything now. It was working fine till i tried fiddling with an AGC addon and an external audio amp. I was experimenting with the voltage supply and turned up the knob of my variable supply to increase voltage, at around 19~21v suddenly every thing went silent with a light 'pop' sound on the earphones. I went back to the original v4 audio setup minus all the addon's - but no sound at all.

It seems the transmit chain is working properly, as i can transmit to a dummy load and observe waterfall from a nearby SDR receiver, i can see and hear sending  with my cw key as well as my voice on the SDR receiver but with cw there is no sidetone volume at the ubitx speaker at all. Everthing is just quiet. I had the KD8CEC ver 1..2 installed and that part seems to be fine, i can PTT, send cw, voice and all menus are available and seem like woking, i can change all menu options and verify them using the ubitx manager as well as upload other versions. But no sound.

I tried the raduino diagnostic by VK2ETA and the tests are OK. I am trying to figure why the sidetone volume could not be heard , the only faint clicks i hear on the speaker are when my multimeter leads are touching the leads on Q72, Q73.

Could i have fried the Q72, Q73 as well as Q71 or any other transistor. I have some basic skills in electronics and i have checked resistor values in the audio amp section and they seem OK, also continuity from R250 till the base of Q71 is OK. Also, it seems to me Q72, Q73 might have failed as resistance values across all junctions seem very low. I had also tried  bypassing the audio section by connecting a speaker between the R250, R251 junction and ground - but again no sound of the sidetone.

I am trying to get the sidetone sound up first and then check the other receive sections - any help would be useful.

Sumit Basu

ajparent1/KB1GMX
 

Sumit,

You grossly over voltaged the LM386 audio amp.
Other parts are likely suspect but start  there.

Start at the speaker and work back.

FYI: the only parts that would tolerate more than 15-16V would be the finals IRF510.

Allison

MVS Sarma
 

I do work T 19v using a laptop adopter selected for low ripple. But , I DO TAKE CARE  that a 12v 2 amp regulator supplies to blance circuitry other than the final IRFs. There also the current is adjusted to say 80mA.
If the due care is not taken , obviously components would fail. Om Bose might take a cue from Allison's advise.

Satma vu3zmv



On Sun, 15 Sep 2019, 6:54 pm ajparent1/KB1GMX, <kb1gmx@...> wrote:
Sumit,

You grossly over voltaged the LM386 audio amp.
Other parts are likely suspect but start  there.

Start at the speaker and work back.

FYI: the only parts that would tolerate more than 15-16V would be the finals IRF510.

Allison