uniden ax-144 diagnosis

[zcapri4me]

Hey all! I have a uniden ax-144 that the am/lsb/usb lights do not illuminate in any position. The display for the channels works/changes when turned. Keying the mic causes the transmit/receive light to turn red and when released, turns green. No meter movement when keyed. Light noise in speaker on receive. Caps appear ok, radio has been in climate controlled storage for awhile. Has anyone had anything similar or any ideas where to look first. Just starting to look over the service manual. Any help would be greatly appreciated. Ron.

[2600]

I would check the center pin of TR35. Should be around 9 Volts DC.

Here's the schematic and layout from the Wayback Machine:

web.archive.org/web/20190127091809/http://www.cbtricks.com/radios/uniden/ax_144/index.htm

Just making sure TR35 is soldered securely may be important.

73

[zcapri4me]

Thanks 2600, I will check that in the morning. Thanks for the quick response. Ill post the results. Ron.

[zcapri4me]

Hey 2600, Im having problems finding the transistor you were asking me to check. I see it in the schematic, but cant find it on the board and I cant find a component locator illustration of the board and parts. Any idea what this transistor is close to? Thanks, Ron.

[2600]

The layout diagram for that radio is a bit grubby. Doesn't seem to show TR35. If you can find the uPC1182 audio power chip, TR35 is a TO-220 transistor on the same heat sink, mounted forward of the audio chip. Schematic says it's a 2SA473. Would be marked only "A473".


Pretty sure. Haven't looked inside one of these in a while.

73

[zcapri4me]

Thanks, Ill check in the AM. At least Ill know roughly where it is, I should be able to track it down. Ron.

[zcapri4me]

Found TR35 ! Center leg reading 8.6V. Went ahead and resoldered all 3 legs of TR35. No change. I dont understand why the leds for am/lsb/usb dont illuminate. Possible PA/CB switch problem? no voltage to that part of circuit? I wish the schematic had voltage test points, maybe could isolate fault. Any suggestions greatly appreciated. This was my first ssb radio, so I have sentimental attachment. LOL.

[zcapri4me]

If anybody else has any ideas, jump on in. I found a voltage chart for ax-144, transistor voltages of all the transistors, so Im going down that road until I narrow it down or somebody comes up with a better suggestion. Thanks to all that read this and any help that they may give.

[zcapri4me]

All transistors seem to be reading in limits. I dont understand the lights that indicate am/usb/lsb not illuminating. That has to play into the problem somehow. Any ideas out there???

[Sandbagger]

Jul 27, 2022 0:09:20 GMT -5 zcapri4me said:

All transistors seem to be reading in limits. I dont understand the lights that indicate am/usb/lsb not illuminating. That has to play into the problem somehow. Any ideas out there???

Either you are lacking a source voltage driving the bulbs, or missing the ground side, or the bulbs are all burned out. Shouldn't be too difficult to determine which it is.

[2600]

The schematic shows the 'hot' side of the LED circuit switched through section 1 of the mode selector. If there is 8.4 Volts on TR35 collector, it's getting lost before it can reach the LEDs.

Or R422, the ground side of all 3 LEDs is bad.

Or the contacts in the mode selector are so crusty the LEDs can't get current.

Or all 3 LEDs are blown?

Finding R422 on the circuit board with the LEDs is where I'd check for voltage first.

Next I'd probe the anode of each LED while the mode selector gets twisted.

73

[zcapri4me]

Thank you so much for looking and relaying the testing info. I will check them and give an update as to progress and hopefully a repaired radio. 73's