crt 3900 EPT360014b SWR switch wiring

[RussJH]

Radio has swr/cal pull switch to open up the bands.

Has anyone a picture of this switch so we can work out how to wire it please ?

[cb4ever104]

I don't have any pictures of it . Maybe Claude does . I presume it just removes the +8V to the band switch , defaulting the radio to the FCC band . To bypass it will be an easy job to do . All you'll need is a DVM . Find the 2 wires that are connected to the switch (+8V and band switch) . Disconnect them and then solder them together .

Sammy

[RussJH]

Thanks Sammy, that's useful, the problem is the switch was removed and the photo taken has corrupted, so we have 7 wires floating about ..

[cb4ever104]

7 wires Russ ? So the whole SWR/CAL with the switch has been removed . Even so , the EPT boards are really well marked . Most of the wires will go to the JXXX connectors at the front , and they're all labelled on the pcb . The band switch wire is usually purple , although I can't remember how it's marked on the JXXX connector . The +8V is marked "+8V" I think . I'm away from home just now as well , so I can't open up my radios to have a look . There's a decent diagram of the 14B I think on cbtricks.com . If you can't figure it out then let me know and I'll try and find it .

Sammy

[RussJH]

7 wires Russ ? So the whole SWR/CAL with the switch has been removed - Correct !

Ideally would like to rewire the switch, however if not, then will try the bypass.

Much appreciated Sammy

[cb4ever104]

Hi Russ . The variable SWR control needs 3 wires . Earth wire to one side of the pot and the center and the other one pin wires go to the RF/SWR switch . I've attached a diagram . You'll need to figure out which one's which . If you tell me where the remaining wires go , and any pcb labels , then I should be able to tell you how to wire the band switch part .

Untitled.jpg

Cheers

Sammy

[14CS06]

Hello

please look at this pics











Schematic



@+
Claude

[cb4ever104]

Thanks Claude

[RussJH]

Superb, many thanks to you both.

[RussJH]

The mystery continues. We can't seem to get it to bypass by connecting 8v(purple) and the green that goes to the band switch. Radio is still stuck on mid block, which is odd.

We have the following :-

Blue wire (goes to 10 kc shift)
Green wire ( goes to "TONE" on board)
Yellow wire - goes to J104
Orange wire (has diode) - goes to J104
Purple wire (to B+ - this is 8v)
Green wire (goes to band switch)
Red wire (goes to "AMP" on board)

Any ideas please ? Our small brains are getting a bit frazzled now.

Many thanks

Russ

[cb4ever104]

Is there a little jumper on the board near the front ? If so then it might need moving ? I don't have a photo , but it's in the middle section near the front .

You need to make sure that the +8V is entering the band switch and being sent out onto the pins marked A,B,C,D,E,F on JXXX .

Sammy

[RussJH]

Just to clarify, it was working fine previously to removal of the swr switch

[cb4ever104]

Ah . Well , no need to look for the jumper then . It's hard for me to know what's been done to it without seeing it . The purple wire leaving B+ should normally be the input to the band switch . If yours is stuck on the MID band then it means that your feeding 8V to pin "D" of J104 and the switch is doing nothing .

[cb4ever104]

I'm looking at the picture Claude posted . The purple is the key . It looks as if the green and yellow are connected to the same pin . If the radio is on FCC with the switch pushed in then it looks as if the +8V purple is connected to green and yellow when on the MID band . So solder the yellow and green together and the purple should be soldered to the orange wire with the diode to open up the bands .

[14CS06]

Hello

Thank you to display your pictures to be able to help you

@+
Claude