Parting out Realistic DX 440 Receiver

Status
Not open for further replies.

Fast1eddie

Member
Joined
Mar 4, 2004
Messages
568
Location
Crafton Pennsylvania
My 440 refuses to power up on internal or external DC, however the display is fine so the fault is somewhere on the DC/DC converter board.....I do not have a service manual and my vision is going so it makes it difficult for me to see the detail I need for a component level repair. My instincts tell me a IC went, thinking this takes external DC, regulates it and breaks it down for various voltages needed for the main receiver board. My loss is your gain, as the used car salesman says.....I am offering the radio for parts, perhaps someone can use it, or repair it for me. Although a older radio, I loved the sensitivity and have enjoyed using it over the years....I'll wait a reasonable time for a taker, if not she goes to the trash.

Classic Collins she ain't.

Good cosmetics, main board is intact and good.

I will even pay for the shipping!
 

Boombox

Member
Joined
Sep 2, 2012
Messages
929
Dumb question time: have you tried to jiggle the molex connector between the logic board and the main receiver board?

From looking at a 440 schematic it seems all the power from the positive side of the battery / AC jack goes to the main receiver board from a two wire, molex connector, so it's probably a thin one.

Or spray it with contact cleaner? It might be easier to see than components, and maybe there is an outside chance that it just got oxidised or a bit off from age.

Just a thought.

73. Boombox.
 

Boombox

Member
Joined
Sep 2, 2012
Messages
929
RE: my previous post:

I was wrong about which connector seems to carry the power to the receiver PCB. After taking a second look at the schematic, the one I described just goes to the power button. Because that part of the schematic (the wiring of the molex cables) is a bit hard for me to decipher, it's difficult for me to tell how the receiver board gets its power.

But there's got to be another connector cable that carries the power to the receiver board. It may be worth it to check / spray all of the connectors & cables, just in case.

Hope you can get your radio fixed before trying to part it out. DX-440's are great sounding SW radios. Especially through a set of headphones. Nice performers, too.
 

Fast1eddie

Member
Joined
Mar 4, 2004
Messages
568
Location
Crafton Pennsylvania
I located a smoked transistor, believe it is Q103 from the schematic, identified as a 2SB808F/G. From the schematic, my interpretation is it functions as a switch when external DC is used, possibly as a first line overprotection/reversed polarity device. And honestly, that's what I did....forgot the 440 calls for 9VDC, I plug it into 12VDC....hey, we're only talking three tiny volts here....it worked before without issue. Now to locate the part, NTE has a good cross reference but since it is a switch, I'll look through my stuff. Wishing my eyes were that of a 17 year old!

You're right, the 440 is a sweet radio and does a nice job processing the signals.....Although it has some quirks, it remains a excellent performer.

Thank you for your help!
 

Boombox

Member
Joined
Sep 2, 2012
Messages
929
I have a service manual, but the schematic I found on the DX-440 Yahoo eGroup was clearer.

But the service manual has a block diagram, and I just looked it over.

Q203 is one of the voltage regulator transistors, so it makes good sense. Tracing the connectors as best I can (which is very shaky) it also affects the power to the receiver board, and has a connection to the DC jack. (DC jack through R309 to pin 8 on Molex connector L; pin 8 on connector L to pin 1 on connector B; pin 1 on connector B to the collector or emitter of Q203. The output (?) of Q203 seems to hit one leg of the RF gain control, and then the receiver board).

Glad you were able to find the problem, and good to hear you are going to try to keep the 440 going. :)
 
Status
Not open for further replies.
Top