President Jackson No TX No RX switching

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timrim
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President Jackson No TX No RX switching

Postby timrim » Thursday 4th Dec 2008, 8:18

Radio Make and Model: President Jackson
PCB Number: PB042
PLL Number: MC145106P
Test gear available: Full lab setup
Symptoms: No TX and RX Switching

What is working: It lights up

What has been tried:
Tested TR31, TR32, TR33,
D59, D61, D66 check ok on ohm meter
Pulled and tested R187,R202,R168,R203,R175


Did it suddenly happen ?: Customer brought radio in that way

Anything else that may be of help?:
Voltage checks on the following transistors:
TR31 E=7.7 B=8.3 C=8.8
TR32 E=0 B=.65 C=8.4
TR33 E=8.8 B=3.2 C=2.5
The voltages do not change from receive to transmit at all

I am getting 8 volts receive and 0 volts on TX on the cathode of diodes D59 and D61

Voltages on IC4 as follows

1.-8.6
2.-4.7
3.-4.7
4.-4.7
5.-0
6.-1.8
7.-8.8 Receive 2.8 Transmit
8.-1.4

On the above IC, only pin 7 changes on transmit

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Rick
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President Jackson No TX No RX switching

Postby Rick » Thursday 4th Dec 2008, 10:48

What is the voltage at Pin 8 of the PLL (IC5)?
What happens if you unhook one end of R171?
Rick.

timrim
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President Jackson No TX No RX switching

Postby timrim » Thursday 4th Dec 2008, 12:08

0 volts on pin 8, so that means the PLL is unlocked

I did not suspect that, because when I got the radio TR 33 was bad and I replaced it, so I assumed the problem had to be in switching...Another lesson learned!

Unhooking 1 end of R171 allows the receive light to go out when I press transmit, but no transmit or receive. With R171 hooked up, the receive light stays on all the time.

timrim
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President Jackson No TX No RX switching

Postby timrim » Thursday 4th Dec 2008, 12:21

I just found out why the PLL was unlocked, C97 was shorted (10volt cap)

Radio now receives, transmit not working, transmit light not working.

Voltage on pin 8 of PLL is now 8

OK now for the new voltage readings on the following:

TR31 E=7.7 Rx 0volt Tx B=8.3 Rx 0 TX C=8.8

TR32 E=0 B=.8Tx 0Rx C=8.4Rx 0Tx

TR33 8.8 B=3.2Tx 0Rx C=2.5Rx 0Tx

On receive the roger beep tone is constantly playing, and heard in speaker.



EDIT: Radio is now fixed!
Thanks Rick for the clue, thats all I needed!

timrim
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President Jackson No TX No RX switching

Postby timrim » Thursday 4th Dec 2008, 17:06

Has anyone else discovered that the schematic calls for a 2SD355E for TR31 and a 2SB525 for TR33, but yet the radios actually come with 2SD355E installed in both locations, apparently they had TR33 in backwards with a 2SD355E, and it must have worked, but I simply replaced TR33 with a 2SA473, and it fired up.
The odd thing is, both of the 2SD355E transistors are NPN, but TR33 on the schematic is a PNP.

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Rick
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President Jackson No TX No RX switching

Postby Rick » Thursday 4th Dec 2008, 21:37

TR33 must have been change at some time for the wrong one, as NPN would be switch on all the time and RX/TX would be in conflict.

I have seen the TR33 fitted in the wrong way round a few times, after the transistor as failed.

I use a 2SA1282 in most radios, which use this form of RX/TX switching.

A word of caution using a 2SA473 as the TX switch is not a good move, if the TX line ever went short it will take out the track on the PCB and could also take out the main regulator.
Rick.

timrim
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President Jackson No TX No RX switching

Postby timrim » Thursday 4th Dec 2008, 21:50

Thanks for the reply Rick, I have some 2SA1282's so I will swap that out to keep things safe.

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President Jackson No TX No RX switching

Postby SuperBad » Thursday 8th Jan 2009, 9:53

Did you ever get this running. I have one that my Dad inherited & is doing the same thing. Some times it works for a few mins till it warms up. Then it quits. Strange thing that if you turn it to the freq a it will key, but anything higher it will not. Every now & then it will come on and talk on all channels. But not often. Any suggestions? Thanks

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President Jackson No TX No RX switching

Postby timrim » Thursday 8th Jan 2009, 17:11

Yes, it was fixed. I replaced TR-33 and C-97.

In your case, it sounds like the VCO may need adjustment.

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President Jackson No TX No RX switching

Postby SuperBad » Friday 9th Jan 2009, 2:35

Weird thing is. When I key it up & its not working. I get talk back thru the speaker. Does this still sound like the VCO & if so how do I adjust it?

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President Jackson No TX No RX switching

Postby timrim » Friday 9th Jan 2009, 19:14

Well if your radio only keys on the a band, or if you start going up in frequency and the transmit drops out, it could be the VCO. Does the radio receive ok on all bands and channels? If so, than the VCO should be ok, then I would suspect an alignment issue between the TX mixer and output stages.

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President Jackson No TX No RX switching

Postby SuperBad » Saturday 10th Jan 2009, 2:13

Well I found it last night. I broke out the old pencil & started poking with the eraser. And found a cold solder. It was around the 3 ic chips on the left side of the radio that are all right there together. But she is a talking now. 10-4!!!! Thanks. :D

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President Jackson No TX No RX switching

Postby SuperBad » Sunday 11th Jan 2009, 11:06

K I have another question. Everything is working fine. And I guess maybe the VCO might be out on the a.m. a little don't know. On the am side if someone is in close range the sounds sounds garbled or warrble. But if they are a good distance I can hear them fine. If I turn down the rf I can hear someone close. This is only on the am side. Nt ssb or fm. What can I do to resolve this?

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Re: President Jackson No TX No RX switching

Postby SawzAll » Friday 26th Jul 2013, 15:25

Got a SS /JA radio; which is almost the same radio as the Jackson.

It also has the SAME TX problem here. RX is fine; but if I key the mic the TX indicator doesn't light.

PLL voltage is OK; The TX switch transistor is OK too.

New to fixing radios and a bit stumped here; any other things to look at?

Like this forum and this is my first post!


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