Galaxy DX2517 10.240Mhz osc off frequency

[Tolteca]

Ah duhhhh. Did not realize that was the tap they were talking about. Stupid me hahaha.

Alright so that has been adjusted but unfortunately though power did go up a tad bit the problem remains.

What other radios use this same board? I also have a problem with the roger beep and can't quite figure out where that is. The roger beep stays stuck.

Edit: Just saw that other radio info, thanks!

I tried with another mic just to confirm it wasn't low audio from the mic and it acts the exact same. So we have a bit of low tx and rx on side band.

 

[Handy Andy]

ITs funny you ask about Roger Beep...



Roger beep was way back in the old days - they kept it in for some reason.

Now, you have CW in that radio too - but they added in thru the Audio chip for your listening pleasure (VR8 controls its volume).

Roger beep adds in thru the MIC amp and hence the days of yore' - the NASA Space Cadet Candidate...

:+> Andy <+:

 

[Tolteca]

This roger beep thing is driving me nuts. I can't figure out this keying circuit.

Here is the problem. When the roger beep is on, it has the normal duration. When the roger beep is off it stays stuck until i turn the radio off then back on again or switch modes into side band. Before it was staying stuck even when the roger beep was on the on position but changing the duration cap seems to have solved this issue. Now it just stays stuck when it's on the off position.

Now for some reason it doesn't actually produce the roger beep tone anymore and the radio just stays keyed up as described above.

EDIT: Got it to beep again, transistor I moved while checking over somethings was shoring out together with a cap.

I've also discovered that when I touch the negative side of the duration cap or a few of the pins on the 4558 IC the tx becomes unstuck. Almost as if I was discharging a mosfet through my finger.

 

[Handy Andy]

May mean a blown diode - look at the schematic above for a diode D66 - may be blown - so it's "stuck".

The radio also has power coming into it from the ECHO board. So it is my fear that the TX/RX switching side of the 4558 may be weak. The latching up is a good indicator of damage in the TX switching area.

One more thing to check, How's Q60 - the darlington that switches in the limiter - if the "Beep" is pretty bloody, then that MAY MEAN THE POWER TO THE 4558 is affected too. The 4558 may be "Stuck on" due to D59 or D66 - check them real quick - Q60 should only have power to the base when in TX mode in PA mode - turns off the limiter. IF D59 blew, then the limiter is always working - and hence the roger beep too.

But that may also mean the TX / RX Toggle section Q30, Q31 and Q33 are possibly damaged too.

Check Pin 7 of the 4558 - TX it's one state - RX is another - if its' steady no matter what - then check the "power good - lets' go" is it gone? Like - check status of RX and TX lights - if they toggle - fine, moving on...

Audio and beep all the time? Eww - then Q33 may have failed if you're getting "talkback or beep" all the time it's the MUTE for the Audio Amp chip along with Q36.

Lots to look at but were checking for toggle function.

:+> Andy <+:

 

[Tolteca]

It seems the problem is somewhere around the inputs of IC7. Pins 5 and 6 do not correspond with the voltage chart posted earlier. The chart says the following

PIN 5 RX=2,54 TX=4.47
PIN 6 RX=2.40 TX=7.63

Instead I get

PIN 5 RX=3.85 TX=3.24
PIN 6 RX=3.30 TX=3.30

I tried changing the actual IC and though it worked perfectly for a moment, the fault ended up coming back. That's the other thing, sometimes it works fine and sometimes it doesn't .


That weird effect I talked about earlier is still there, it happens when I touch certain pins of IC7. For example if I touch either pin 6 or 7 with the probe of my mutlimeter to try and measure their voltages, the fault goes away completely. As soon as I take the probe away it goes back to it's old habit of getting stuck while the RB is off and working normally when the RB is on. On the other hand if I touch pin 5 with the probe of my multimeter, the RB gets stuck on both RB switch positions. Keep in mind again that the roger beep only sticks when the roger beep switch is set to off. The voltage output at Pin 7 is normal and toggles accordingly once the radio is done transmitting or receiving.

It's almost like something oscillates or is sensitive to a bit of capacitance. I'm gonna check diodes related to pins 5 and 6 of the IC.

Am I right to assume that the way this circuit works is by using that half of the 4558 as a comparator? Then at the ouput of that the high low signal is used to toggle the other switching transistors?

I checked the diodes you mentioned and they seem to be fine.

 

[Handy Andy]

Yes, the 4558 is a comparator...1/2 of it anyways... Pins 5 and 6 to toggle 7.

Hows the PLL doing? The 4558 - when it goes "undecided" where pin 5 and 6 ARE EQUAL the PLL is out of lock. It uses the status of POWER GOOD - AND-ing the inputs to make sure the PLL is in lock, and there is a locked frequency.

PIN 6 of the PLL - so we may be onto something. ALSO Check power supply feed to Pin 9 of the PLL when you RX and TX - make sure it's STEADY and roughly 8 volts.

Also - "jiggle the channel selector" it's got a cam on it that has to have a switch short to ground for good output from the selector for the AND gates to properly set the PLL programming pins...This is Pin 1 of the channel selector and the ground of the channel selector header the only one that "grounds" the whole mess...

:+> Andy <+:

 

[Tolteca]

Hmmmm. Are you maybe thinking of a different PLL? According to the datasheet Pin 8 is the lock detect of this PLL and Pin 1 is VDD. I checked both and they stay fairly stable. I noticed a slight drop of about 0.10v when transmitting but that's about it. If it was the PLL lock detect it wouldn't let the radio transmit at all no?

 

[Handy Andy]

You're correct, sorry got busy over here - but yes. Same. Pin 8

And how that works, if the PLL can't go to the frequency, that pin "sinks" current, forcing low. So the PLL when it's out of lock you're readings are low - note the 7.5 nearly 8V on the pin 6 of the 4558 when it "Works" - once the PLL is in lock, that PLL Pin 8 floats high - tells the 4558 chip thru Pin 6 powers ok - RX enable. TX? How - to TX enable - not only does the condition on pin 6 is met, pin 5 goes LOW (PTT engage) to switch pin 7 high. This is an invert function to set TX mode only. (This is a toggle output the AND-ing comes from Pin 6 and the Pin 8 of the PLL both being high - and so RX turns on too - SQ function restored to set state on front panel)

:+> Andy <+: