Thanks! Those didn't turn up when I was searching for 12 Volt relays. You'd think Amazon would make it easier to for them to get at your money.
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TRC-449 repair
- Thread starter TM86
- Start date
Really. Sometimes I think that Amazon is brain-dead. I search on Amazon, " spst relay 12vdc coil." Good little relays. I use a lot and never had one fail. Mount them with double-sided tape.
J. J. 399
Got into the signals around the VCO today. Found TR35 collector at 5 Volts. Sam's says it should be 1.75 Volts or so. Hoping for an easy fix, swapped it out. Didn't help. I also noticed pin 4 on the PLL is also sitting at 5 Volts. Since that's supposed to be an active filter output that's probably not a good thing. Sam's tells me it should be about 2.76 Volts.
I'm going to open the gates for suggestions here because I really don't want to swap the PLL.
I'm going to open the gates for suggestions here because I really don't want to swap the PLL.
TM86 -
If you have a scope, you can use it to look at the PLL and VCOs outputs. The TRC458 service manual is on the forum and shows PLL's waveforms on page 9. https://www.worldwidedx.com/threads/realistic-trc-458-factory-service-manual.239907/
458 is the same as 449 except on board power supply. Check out pages 9 - 12. Great explanation of the 858PLL circuit. Also a block diagram where you can see where everything is going.
TRC449 Schematic is on CB tricks, and is the FACTORY Schematic which I trust over Sams.
If the rig has been recapped, I would first check that the polarities of all the caps is correct. Then do a complete alignment of the PLL circuit, and see if the unit will lock up. If you can't get it to align, you can come back here and then we can figure out the problem. The 858 AM/SSB sets are high quality, and major component failures are rare. Usually problems are due to screwdriver jockeys not knowing what they're doing. Good Luck
- J.J. 399
If you have a scope, you can use it to look at the PLL and VCOs outputs. The TRC458 service manual is on the forum and shows PLL's waveforms on page 9. https://www.worldwidedx.com/threads/realistic-trc-458-factory-service-manual.239907/
458 is the same as 449 except on board power supply. Check out pages 9 - 12. Great explanation of the 858PLL circuit. Also a block diagram where you can see where everything is going.
TRC449 Schematic is on CB tricks, and is the FACTORY Schematic which I trust over Sams.
If the rig has been recapped, I would first check that the polarities of all the caps is correct. Then do a complete alignment of the PLL circuit, and see if the unit will lock up. If you can't get it to align, you can come back here and then we can figure out the problem. The 858 AM/SSB sets are high quality, and major component failures are rare. Usually problems are due to screwdriver jockeys not knowing what they're doing. Good Luck
- J.J. 399
Original Service manual and schematics here. Cause I love a good mystery (& 858 radios).
Start the popcorn please. I will watch from my front row seat!
73
David
Start the popcorn please. I will watch from my front row seat!
73
David
For both the collector of TR35 and PLL pin 4 to be at 5v, either TR35 is not working, R146 at the emitter is open, R150 at the base is open, or the VCO is shorted between the varactor/base and 5v supply. I think the VCO can be eliminated because it is outputting a signal consistent with an out of lock condition, besides, the diagram for it doesn't even make a short to hot look practical.
You swapped the transistor with no change, so that leaves two resistors to check. Either the base is not getting the 5v (present on pin 4) because R150 is open (R150 fails test if TR35 base is at 0v) or because R146 is open keeping the emitter floating (R146 fails test if of it ohms open). R149 becoming a dead short could do it too, but very unlikely.
Edit: I originally said to check the emitter voltage, but thats not the best way.
You swapped the transistor with no change, so that leaves two resistors to check. Either the base is not getting the 5v (present on pin 4) because R150 is open (R150 fails test if TR35 base is at 0v) or because R146 is open keeping the emitter floating (R146 fails test if of it ohms open). R149 becoming a dead short could do it too, but very unlikely.
Edit: I originally said to check the emitter voltage, but thats not the best way.
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R150 and R149 form a voltage divider that, with the correct PLL voltage, supplies .9v to the base, which would put .3v on the emitter.
With 5v from the PLL, the divider puts 1.5v at the base and .9v at the emitter.
If there is .9v at the emitter and 5v at the collector, either the collector is open or R146 is open. I can say that for sure because with .9v at the emitter, there would be .3mA through R146, and therefore .3mA through R147, and since that would drop more than the supply across R147, the collector would drop like a rock and be under 1v. The presence of 5v there suggests no current is flowing through the transistor because any current at all would pull down the other side of R147. The trick is to figure out why no current is flowing through TR35 (no base voltage, no emitter path to ground, or a bad transistor)..
With 5v from the PLL, the divider puts 1.5v at the base and .9v at the emitter.
If there is .9v at the emitter and 5v at the collector, either the collector is open or R146 is open. I can say that for sure because with .9v at the emitter, there would be .3mA through R146, and therefore .3mA through R147, and since that would drop more than the supply across R147, the collector would drop like a rock and be under 1v. The presence of 5v there suggests no current is flowing through the transistor because any current at all would pull down the other side of R147. The trick is to figure out why no current is flowing through TR35 (no base voltage, no emitter path to ground, or a bad transistor)..
Thank you for the links to the service info.
Attempted to start PLL alignment, stuck at step 2. Can't get TP7 down to 2 Volts from 5 anywhere in the range of L7 adjustment.
Checked R146 out of circuit. 2699 Ohms. Checked TR35 in circuit, power off, with cheap Chinese component tester. It came back as functional.
VCO is putting out 34.5943 MHz.
Coming out of TR30 that's down to about 730kHz. Which is way too low for any channel.
PLL pin 1 is at 3.361 Volts. Looking at it on a scope it resembles data, so the DC voltage is obviously an average.
PLL pins 2 and 3 are at 0 Volts, with tiny noise spikes. PLL pin 4 is at 5 Volts, with a little bit of noise on top.
The rest of the waveforms on the PLL look correct, or at least pretty darn close.
I have checked that the capacitor polarity agrees with the markings on the board in the PLL section, and around the 7.8 Mhz crystals as well.
TR35 Voltages. Emitter, 0 Volts. Base, 5.4 milliVolts. Collector, 5 Volts. Did notice that the three pads for TR35 appear to no longer be physically bonded to the circuit board. Electrical connections check good with an ohmmeter.
Based on these readings I also looked at R150, 31.65 kOhms in circuit.
And now, a WTF moment. As I was rechecking things, because these readings don't make sense, PLL Pins 2 and 3 are now at 5 Volts, and Pin 4 is now at 17 milliVolts. The VCO is now putting out 34.6010 MHz.
Nothing like a symptom change in the middle of troubleshooting to throw you for a loop. Too bad it's not phase locked.
I did take another look at the other waveforms. The downmix loop frequency is now about 740 kHz, but no other obvious changes.
Went back and checked against what I had posted yesterday, and saw that the downmix loop then was 2.5 MHz.
Yeah, this is going to be a fun one.
Attempted to start PLL alignment, stuck at step 2. Can't get TP7 down to 2 Volts from 5 anywhere in the range of L7 adjustment.
Checked R146 out of circuit. 2699 Ohms. Checked TR35 in circuit, power off, with cheap Chinese component tester. It came back as functional.
VCO is putting out 34.5943 MHz.
Coming out of TR30 that's down to about 730kHz. Which is way too low for any channel.
PLL pin 1 is at 3.361 Volts. Looking at it on a scope it resembles data, so the DC voltage is obviously an average.
PLL pins 2 and 3 are at 0 Volts, with tiny noise spikes. PLL pin 4 is at 5 Volts, with a little bit of noise on top.
The rest of the waveforms on the PLL look correct, or at least pretty darn close.
I have checked that the capacitor polarity agrees with the markings on the board in the PLL section, and around the 7.8 Mhz crystals as well.
TR35 Voltages. Emitter, 0 Volts. Base, 5.4 milliVolts. Collector, 5 Volts. Did notice that the three pads for TR35 appear to no longer be physically bonded to the circuit board. Electrical connections check good with an ohmmeter.
Based on these readings I also looked at R150, 31.65 kOhms in circuit.
And now, a WTF moment. As I was rechecking things, because these readings don't make sense, PLL Pins 2 and 3 are now at 5 Volts, and Pin 4 is now at 17 milliVolts. The VCO is now putting out 34.6010 MHz.
Nothing like a symptom change in the middle of troubleshooting to throw you for a loop. Too bad it's not phase locked.
I did take another look at the other waveforms. The downmix loop frequency is now about 740 kHz, but no other obvious changes.
Went back and checked against what I had posted yesterday, and saw that the downmix loop then was 2.5 MHz.
Yeah, this is going to be a fun one.
Two voltage extremes from the PD, but very similar VCO frequency, 34.5943 to only 34.6010 with a total 180 of the phase detector, that's odd. I would be tempted to isolate pin 5 on the VCO and drive it with an external 1-4v DC and see if the output frequency tracks the DC voltage. Unless they put a jumper there that isn't on the schematic, it looks like TR35 and R147 would have to come out.
Edit, just realized: yet the downmix moved.... somethings definitely strange here. VCO don't move, but PD voltage and downmix does. Did the tripler crystal learn an impossible trick, is there a bad solder joint on a more significant binary input? What the heck...
Edit, just realized: yet the downmix moved.... somethings definitely strange here. VCO don't move, but PD voltage and downmix does. Did the tripler crystal learn an impossible trick, is there a bad solder joint on a more significant binary input? What the heck...
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It already is LOL
So many times when there is a problem like yours it is a mechanical defect, not an electrical one. If the solder pads for TR35 are lifted, maybe there is an open circuit path, poor solder,or a bad connection elsewhere caused when the caps were changed or when a previous tech was working on it. I would get an mag glass or an eye loupe and give the solder side of the board a good close look.
J.J. 399
Had little more time today. The good news is no symptom changes.
I've checked the connections to and around TR35. Joints look OK under magnification, They show continuous connection via ohmmeter readings, even when pressure is applied in different directions. I didn't push that too much as I can see the traces flexing a little.
I did yank R147 to see how the VCO reacts to 0 Volts in on pin 5. It dropped to 32.5 MHz. Reconnected R147, right back to the 34 Mhz range. I then tweaked L7 to get to the right VCO frequency for channel 40 (35.205), because that's where I happened to have the dial set.
No change, still getting 5 V on PLL pins 2 & 3, 17 milliVolts on pin 4, same voltages on TR35.. So at least it's settled into a consistent state of failure.
I also took a look around at the rest of the solder side. Found a spot that I'd missed cleaning up where the Sony bond had corroded the solder. Fixed that, of course. Did not see any cracked joints, though.
I've checked the connections to and around TR35. Joints look OK under magnification, They show continuous connection via ohmmeter readings, even when pressure is applied in different directions. I didn't push that too much as I can see the traces flexing a little.
I did yank R147 to see how the VCO reacts to 0 Volts in on pin 5. It dropped to 32.5 MHz. Reconnected R147, right back to the 34 Mhz range. I then tweaked L7 to get to the right VCO frequency for channel 40 (35.205), because that's where I happened to have the dial set.
No change, still getting 5 V on PLL pins 2 & 3, 17 milliVolts on pin 4, same voltages on TR35.. So at least it's settled into a consistent state of failure.
I also took a look around at the rest of the solder side. Found a spot that I'd missed cleaning up where the Sony bond had corroded the solder. Fixed that, of course. Did not see any cracked joints, though.
Almost forgot. I ended up buy the relays you recommended, JJ. It was either 10 for 10 bucks or 25 for 15 bucks. I went with the value sized option. At what works out to 63 cents per relay they were cheaper than anything else I had looked at.
Can't figure out why the vendor puts them in regular styrofoam, wraps that in plastic cling wrap, then puts the whole thing into a sealed static bag. I don't think they actually took a class on ESD. Sure, it's relays so no harm done, but still.
Can't figure out why the vendor puts them in regular styrofoam, wraps that in plastic cling wrap, then puts the whole thing into a sealed static bag. I don't think they actually took a class on ESD. Sure, it's relays so no harm done, but still.
OK, PLL is up and running again. I had swapped it just to be sure, no change. I checked the loop filter caps, both good. Which meant it had to be TR35, since all the passives around it tested good.
But TR35 also tested good in the cheap Chinese component tester. So could it be? Nahhhh... but it was. Darn thing was installed backwards. Base and emitter leads were swapped. Second radio I've run across with a transistor in backwards like this. Which I guess is why they're cheap on fleaBay.
Once I got that installed correctly I was able to adjust L7 to get TP7 to 2 Volts on AM channel 1 just like the service manual says. I'm going to let this cook for a while and start over on the alignment procedure to see how far I get before the next problem crops up.
But TR35 also tested good in the cheap Chinese component tester. So could it be? Nahhhh... but it was. Darn thing was installed backwards. Base and emitter leads were swapped. Second radio I've run across with a transistor in backwards like this. Which I guess is why they're cheap on fleaBay.
Once I got that installed correctly I was able to adjust L7 to get TP7 to 2 Volts on AM channel 1 just like the service manual says. I'm going to let this cook for a while and start over on the alignment procedure to see how far I get before the next problem crops up.
- No one is chatting at the moment.