I am trying to repair a galaxy dx2517 with the newer mosfet board. I originally start troubleshooting it because it was outputting almost no power and could not properly adjust bias voltage or current either way I tried. and at some point along the way, it started to switch into tx on its own even in rx after being powered on for about 20 seconds. I'd let it cool off and turn it back on and it did this consistantly after being on for 20 seconds. And now when you power on the radio it immediately tries to switch into rx and tx at the same time and the rx/tx led on the front looks like the red and green light are on together. I've been going through checking parts in the rf driver and final sections, the regulator section near the q37 regulator, and in the tx,rx switching circuit around the q30 through q33 switching transistors and have not found a problem yet. after checking most of the components in these areas I have yet to find a shorted part or problem. I've started replacing a few electrolytics, regulator transistors, a few diodes. I've reflowed some of the areas of solder and have not seen a cold solder joint. I have been careful in soldering and using another galaxy board to compare and haven't found any bridged connections. No dark burnt components. I do have a temperature gun to check for hot areas, I'm hoping someone more knowledgeable can offer some advice and point me in the right direction of where/how to trace the problem. I do not want to give up on this radio since I am learning how to troubleshoot as a hobby. I have minimal experience under my belt and hoping to fix this one to learn something from it. I am new to this forum and hoping I'm in the right place for some coaching. I'm hoping to fix the tx switching problem so I can go back to troubleshooting the bias voltage issue. I can check voltages or anything else at someone's request. The driver and finals are removed while I've been troubleshooting, hopefully that's not a problem. thanks in advance!
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Galaxy DX2517 Troubleshooting Help
- Thread starter Junkyarddog76
- Start date
What if the bias board, the driver, and both finals are already removed and it still does this? I think I’ve even tried removing q54 regulator and changing it and it does not fix it.
I found the thread where I broke down the keying circuit on a 55v. I think it is the same. Check it out if you want to know how to troubleshoot that part of the circuit.
The first thing I would check is the KB362 diode (D71, its two diodes built into one package). I will skip the detailed explanation as it is already in the linked thread.
The first thing I would check is the KB362 diode (D71, its two diodes built into one package). I will skip the detailed explanation as it is already in the linked thread.
This is the keying circuit redrawn to make it easier to see whats going on.
There is a reason Cable Guy asked about the voltages on pins 5, 6 and 7. Let me explain how this circuit works.
R166 and R169 form a voltage divider to provide a reference voltage of 38.4% of the regulated supply and feeds it to the op amp for comparison.
R167, R171 and R168 also form a voltage divider that changes value depending on whether the PTT is pressed or not. R168, being at the output of the op amp (which goes high and low) is effectively switching between being in parallel with R167 and...
There is a reason Cable Guy asked about the voltages on pins 5, 6 and 7. Let me explain how this circuit works.
R166 and R169 form a voltage divider to provide a reference voltage of 38.4% of the regulated supply and feeds it to the op amp for comparison.
R167, R171 and R168 also form a voltage divider that changes value depending on whether the PTT is pressed or not. R168, being at the output of the op amp (which goes high and low) is effectively switching between being in parallel with R167 and...
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That diode was famously vulnerable to getting toasted by touching ground on a loosened mike socket in mobile radios with that circuit board. Even briefly touching grounded metal would pop it. We adopted the habit of lap-soldering three 1N4148 diodes in series, to replace D71. For some reason just two of that diode would not always behave properly. Three of them always seemed to. A plastic sleeve over the series string would prevent a repeat of ground contact.
I suppose the original KB362 could be had, but with plenty of 1N4148 on hand, just couldn't justify the time and cost of stocking it. A diode test of that part should read around 1.3 10 1.4 Volts or so.
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I suppose the original KB362 could be had, but with plenty of 1N4148 on hand, just couldn't justify the time and cost of stocking it. A diode test of that part should read around 1.3 10 1.4 Volts or so.
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I've been studying that thread to understand the circuit better. I cant check voltages for rf and tx because it's stuck in tx or both. But the voltages on IC7 are:I found the thread where I broke down the keying circuit on a 55v. I think it is the same. Check it out if you want to know how to troubleshoot that part of the circuit.
The first thing I would check is the KB362 diode (D71, its two diodes built into one package). I will skip the detailed explanation as it is already in the linked thread.
This is the keying circuit redrawn to make it easier to see whats going on.
There is a reason Cable Guy asked about the voltages on pins 5, 6 and 7. Let me explain how this circuit works.
R166 and R169 form a voltage divider to provide a reference voltage of 38.4% of the regulated supply and feeds it to the op amp for comparison.
R167, R171 and R168 also form a voltage divider that changes value depending on whether the PTT is pressed or not. R168, being at the output of the op amp (which goes high and low) is effectively switching between being in parallel with R167 and...
Pin 1: 4.95v Pin 8: 8.95v
Pin 2: 4.95v Pin 7: fluctuates heavily from about 0.8 to 2 volts or so
Pin 3: 4.95v Pin 6: 3.6v fluctuates very slightly from 3.4 to 3.6v
Pin 4: 11mv Pin 5: fluctuates heavily from about 1.8 to 3.6 volts
A few other measurements were:
R169- 9.55v on the left lead from the top, 9.25v on the right lead from the top
R167- 0v on either lead from top
R168- 0v on either lead from the top
Here and there I'll hear a little static trying to come on and off like maybe it's trying to switch back and forth. I've been checking diodes and transistors when I can and I have not found a shorted diode or transistor yet. I also can't check certain things on your hand drawn schematic because I cannot for the life of me find q38(while I can see q37 on the heat sink and q39 on the board) and I also cannot find R166.
Can anything be determined from these measurements to help direct me in the right area? I don't understand why there is 9 volts on either side of R169 when one end is supposed to be grounded and the other end meets pin 6 of IC7 when there is 3.6 volts right on pin 6, not 9 volts like at R169.
I also noticed q35 was burning up after I replaced factory D72 with 2 series 4148's so I listened to what one of you guys said and tried adding a 3rd diode in series and it stopped getting hot. So I guess for the rest of those diodes I replace I'm going to just start using 3 in series which got me like 1.7v drop.I found the thread where I broke down the keying circuit on a 55v. I think it is the same. Check it out if you want to know how to troubleshoot that part of the circuit.
The first thing I would check is the KB362 diode (D71, its two diodes built into one package). I will skip the detailed explanation as it is already in the linked thread.
This is the keying circuit redrawn to make it easier to see whats going on.
There is a reason Cable Guy asked about the voltages on pins 5, 6 and 7. Let me explain how this circuit works.
R166 and R169 form a voltage divider to provide a reference voltage of 38.4% of the regulated supply and feeds it to the op amp for comparison.
R167, R171 and R168 also form a voltage divider that changes value depending on whether the PTT is pressed or not. R168, being at the output of the op amp (which goes high and low) is effectively switching between being in parallel with R167 and...
Before i get too far into reading this, I think I should point out that the component numbers in my schematic are for the 55v, not the 2517. For instance, R169 in a 2517 is the supply for the balanced modulator, so reading rail voltage there is expected.
I think I should re-draw the switching schematic to show the part numbers used in the 2517.
I think I should re-draw the switching schematic to show the part numbers used in the 2517.
Ohhh okay haha that would make complete sense I just assumed it was the same. If you were able to do that, that would be awesome then I could try taking a second look at it with the new schematic and maybe be less confused.
I'm accustomed to just pulling out Q30, 31 and Q33 to test each. D70 and 71 can be tested in circuit. The voltage on IC5 pin 5 has to be higher than pin 6 to make the radio receive. This should put at least 8 Volts onto pin 7. If the voltage on pin 7 is too low, Q33 will partially turn on, activating transmit circuits while the radio should be receiving.
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