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Uniden Washington
- Thread starter Ben Hebert
- Start date
Next thing to check is L22, just to the right of D33 in the pic above. The green wire should feed 8 Volts DC into L22, out the other end of L22 into the anode (not banded) end of D33. You should then have about 6/10 of a Volt DC less than that on the banded (cathode) end of D33. The solder pad where the green wire solders to the pc board should have 8 Volts DC in USB only. If it doesn't, this points to a bad mode-selector switch.
73
73
The crystal for USB X2 is also used for AM transmit (only). Can't be a bad crystal if the radio transmits on AM.
I would check the exposed lead (cathode) of D27, since it is the last stop in the current path that selects X2 to run in USB mode.
You should have between 6 and 7 Volts DC more or less in both SSB modes while receiving. The voltage should drop to about zero in AM receive, and then show about the same DC voltage as SSB while in AM transmit.
If this reading drops in a big way in USB mode, we have narrowed it down to a mode-switching problem in the carrier oscillator.
73
I would check the exposed lead (cathode) of D27, since it is the last stop in the current path that selects X2 to run in USB mode.
You should have between 6 and 7 Volts DC more or less in both SSB modes while receiving. The voltage should drop to about zero in AM receive, and then show about the same DC voltage as SSB while in AM transmit.
If this reading drops in a big way in USB mode, we have narrowed it down to a mode-switching problem in the carrier oscillator.
73
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I think we are running out of simple stuff that can be checked with just a volt meter alone.
Do you have any kind of shortwave or ham receiver that can tune in to 7.8 MHz?
Could be that my assumption that the 7.8 MHz oscillator is shutting down in USB mode is not quite right. Just the single most-common way to make one sideband mode go dead.
If you put a coax jumper on the receiver and unthread the shell of the plug on the far end back down the coax, you now have a half-inch long 'sniffing' antenna on the end of the jumper. Holding it close to X2 and X3 should allow you to hear a carrier at 7.8015 MHz in USB mode, and 7.7985 MHz in LSB mode.
If both of those can be heard, the problem lies elsewhere.
73
Do you have any kind of shortwave or ham receiver that can tune in to 7.8 MHz?
Could be that my assumption that the 7.8 MHz oscillator is shutting down in USB mode is not quite right. Just the single most-common way to make one sideband mode go dead.
If you put a coax jumper on the receiver and unthread the shell of the plug on the far end back down the coax, you now have a half-inch long 'sniffing' antenna on the end of the jumper. Holding it close to X2 and X3 should allow you to hear a carrier at 7.8015 MHz in USB mode, and 7.7985 MHz in LSB mode.
If both of those can be heard, the problem lies elsewhere.
73
So, here's the dilemma.
The radio works for LSB and AM modes. This crosses a lot of suspects off the list, since they would cause trouble on the two modes that DO work.
The crystal used for USB must be okay, since that crystal is used for AM transmit.
The 'cans', coils used to trim the crystal frequencies when changing modes are only in the circuit for the other two modes. In USB mode, both the 11.1125 MHz crystal and the 7.8025 USB carrier crystal have only a switching diode in the circuit. Those coils are in the circuit ONLY in the other two modes, the ones that work. In USB mode, only a diode is in line with either crystal.
An open diode would disrupt the DC-voltage readings that he took, so that seems unlikely. He checked the voltage at the resistor that completes the ground return for the switching diode for D27, D29 and D33 so you can't blame them. An open diode would disrupt that measurement.
Makes my theory that the 7.8025 crystal is shutting down in USB mode seem questionable. Next thing I would have done is to look for that 7.8025 carrier with a 'scope, to see that the level is okay, and listen for it with the SDR to see that it's on frequency.
And that's where we left off. He doesn't have the tools on hand to eavesdrop on the 7.8025 and confirm if it's alive or dead in USB mode.
73
The radio works for LSB and AM modes. This crosses a lot of suspects off the list, since they would cause trouble on the two modes that DO work.
The crystal used for USB must be okay, since that crystal is used for AM transmit.
The 'cans', coils used to trim the crystal frequencies when changing modes are only in the circuit for the other two modes. In USB mode, both the 11.1125 MHz crystal and the 7.8025 USB carrier crystal have only a switching diode in the circuit. Those coils are in the circuit ONLY in the other two modes, the ones that work. In USB mode, only a diode is in line with either crystal.
An open diode would disrupt the DC-voltage readings that he took, so that seems unlikely. He checked the voltage at the resistor that completes the ground return for the switching diode for D27, D29 and D33 so you can't blame them. An open diode would disrupt that measurement.
Makes my theory that the 7.8025 crystal is shutting down in USB mode seem questionable. Next thing I would have done is to look for that 7.8025 carrier with a 'scope, to see that the level is okay, and listen for it with the SDR to see that it's on frequency.
And that's where we left off. He doesn't have the tools on hand to eavesdrop on the 7.8025 and confirm if it's alive or dead in USB mode.
73
certainly not trying to derail Nomad's efforts, but can't find in the thread where D33 is confirmed good.
Did i miss that?
Ben, if you haven't already, could you measure the voltages on both sides of D33 while in USB mode?
the voltages you listed here seem odd.
the "green wire pad" should have the exact same voltage as L22 as they are connected.
the L22 side of D33 should have the 8 volts on it, and the other end of D33 should have about .6 volts DC less than that.
if you can confirm that D33 does indeed work, it will at least shut me up long enough for Nomad to get his point across LOL.
LC
Nomad, it was here in reply number 16
IF YOU CHECKED - both the trace LEADING TO D33 and the one from D33 to L22 - and the ONE TO D33 FROM THE FRONT OF THE BOARD, SHOWS 7~8Volts - then it means D33 is gone to lunch or the coil can it feeds is open..
So it may have blown open - hence his problem.
Replace D33 with a 1N4148 50PIV 500mA.
Then I see this...
So, once I thought we had it - now I don't know either - unless the coil is open
9 volts? Yikes, sounds like either he moved the ground test lead to another location or there is a separate issue of open line back to the mode switch.
:+> Andy <+:
IF YOU CHECKED - both the trace LEADING TO D33 and the one from D33 to L22 - and the ONE TO D33 FROM THE FRONT OF THE BOARD, SHOWS 7~8Volts - then it means D33 is gone to lunch or the coil can it feeds is open..
So it may have blown open - hence his problem.
Replace D33 with a 1N4148 50PIV 500mA.
Then I see this...
So, once I thought we had it - now I don't know either - unless the coil is open
9 volts? Yikes, sounds like either he moved the ground test lead to another location or there is a separate issue of open line back to the mode switch.
:+> Andy <+:
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Ok sounds better! Whew - when you "See" voltage that is higher than the source voltage itself, you need to recheck your measurement points - like the old adage, measure twice cut once...applies to electronics as well.
Ok, there is something new too, L22 voltage is higher - I'm presuming you're measuring, but where though - to get this reading?
Why? When you draw DC current thru a wire - the wire itself has a built in resistance or drop as ohmic resistance along it's length - meaning the longer the distance the wire is from the source of DC, the higher it's voltage drop. Meaning, if you're measuring from a long distance away from the source, it shows less voltage arriving to the end of your test leads.
So , L22 "gained" voltage back - but how?
Means we have to see if the other modes are supplying power to the section at the same time.
So that means you'll have to verify the voltage from the mode switch is going to where it should - and not doubling back on itself due to an issue with wiring or isolation problems caused by bad diodes that steer power thru the board while it's in that mode.
Nomad, you have more of the datasheets on this radio that I do - so I can only go so far in helping.
Sorry to interrupt.
:+> Andy <+:
Ok, there is something new too, L22 voltage is higher - I'm presuming you're measuring, but where though - to get this reading?
Why? When you draw DC current thru a wire - the wire itself has a built in resistance or drop as ohmic resistance along it's length - meaning the longer the distance the wire is from the source of DC, the higher it's voltage drop. Meaning, if you're measuring from a long distance away from the source, it shows less voltage arriving to the end of your test leads.
So , L22 "gained" voltage back - but how?
Means we have to see if the other modes are supplying power to the section at the same time.
So that means you'll have to verify the voltage from the mode switch is going to where it should - and not doubling back on itself due to an issue with wiring or isolation problems caused by bad diodes that steer power thru the board while it's in that mode.
Nomad, you have more of the datasheets on this radio that I do - so I can only go so far in helping.
Sorry to interrupt.
:+> Andy <+: