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Post by Deleted on Dec 15, 2010 18:26:17 GMT -5
I picked up a new - old stock TRC-451. From what I read, these have superior receive, and great modulation.
One question. The caps. They have some of those old 10V caps. Should I replace all the caps, or just leave them be?
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Post by Tombstone (R.I.P.) on Dec 15, 2010 19:17:36 GMT -5
If the radio is running well I'd leave the caps alone for now but it's just a matter of time before caps start failing. Just my opinion.
Tombstone
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Sandbagger
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Post by Sandbagger on Dec 16, 2010 9:12:24 GMT -5
I would agree. Unlike tube rigs where high voltage and leaky caps can lead to small explosions, cap failures in solid state rigs tend to be far less dramatic. As long as the rig works ok, I wouldn't worry about it. If those 10V caps start to short, malfunctions will surface, and then you can start replacing bad ones.
The TRC-451 is one of my favorite mobile rigs. It has a really nice receiver with a low noise floor, a very effective noise blanker, and smooth audio on both AM and SSB. It's not a good candidate for channel expansion, but if all you want is a good performing 40 channel radio, it's a good one.
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Post by Deleted on Dec 16, 2010 10:36:07 GMT -5
No channel expansion. Not interested in it. I could get away with single channel CBs. Thanks for the info! Will let it go.
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Post by Deleted on Dec 21, 2010 9:42:59 GMT -5
Well, I received it. Looks new. Have not opened it up yet. SR/F meter is dead on both receive and transmit. Radio check are reporting a squeal.
Also weird, a buzzing noise when you turn the volume all the way down. It is only there when the antenna is connected. It was real loud and then got much lower as the radio warmed. Now only hear it when the volume is all the way down. But it is there.
Also, when I unplug the mic, the modulation LED seems aluminated about half way, and goes away as soon as I plug the mic in. I found that this is related to the buzz, as I disconnect the antenna, the LED goes out completely (with mic unplugged).
Any advice before I dive in?
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Post by Deleted on Dec 21, 2010 9:58:05 GMT -5
OK. I opened it up. First thing is that some long insulating strips fell out, so I need to find where they go. That could be the buzz problem.
SR/F meter is in series with C28. The schematic shows a 22uf - 10V cap. Damn, I'll bet it is the 10V blues!
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Post by Sandbagger on Dec 21, 2010 12:54:35 GMT -5
OK. I opened it up. First thing is that some long insulating strips fell out, so I need to find where they go. That could be the buzz problem. SR/F meter is in series with C28. The schematic shows a 22uf - 10V cap. d**n, I'll bet it is the 10V blues! Nothing is ever easy with you is it? ;-) I doubt that the cap is in series with the meter. DC can't pass through a cap. IIRC there is a cap ACROSS the meter leads. The insulating strips were probably glued to the case where it meets the front panel. The glue dried up and they fell off. Not a serious issue I would think. Also, the TRC-451 is a little unusual in the mic connection department. Where most electronic switched radio will lose receive audio when the mic is unplugged, the 451 will actually lose complete receive (including meter indication) when the mic is unplugged. Make sure you're testing with the mic connected. It is entirely possible (and likely) that there are a few caps in there giving your grief, although I find it interesting that my radio has been working fine for the 15 years that I had it, while yours is NIB and never used and has issues. I guess inactivity is far worse for caps than regular use.
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Post by Deleted on Dec 21, 2010 14:55:58 GMT -5
LOL. Nothing is easy with me. ;D
The insulation came off of the back. I might have a stash of caps. You are right about C28. It is actually part of the TR11 circuit. The cap is not in series.
The receive works well, as does transmit and modulation. I am DKing 4 watts and swinging about 10 or so. So functionally, it is fine. Meter is dead for both, though.
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Post by Sandbagger on Dec 21, 2010 20:17:56 GMT -5
LOL. Nothing is easy with me. ;D The insulation came off of the back. I might have a stash of caps. You are right about C28. It is actually part of the TR11 circuit. The cap is not in series. The receive works well, as does transmit and modulation. I am DKing 4 watts and swinging about 10 or so. So functionally, it is fine. Meter is dead for both, though. Those meters do stick with age and use, but I would think that a NIB unit would not have a problem. You said something about a squeal, what happened to that?
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Post by Deleted on Dec 21, 2010 23:27:06 GMT -5
Dave,
Good news. I have ironed out all the problems except the meter is still DOA. All hums and noises are gone. Radio checks are superb. Will work on the meter problem. Can I manually test the meter by connecting a DMM across the pins?
Question on the dim pot. This is the dual pot with the squelch. Does the dim part go all the way around, without stopping at the limits? Mine does.
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Post by Sandbagger on Dec 22, 2010 8:00:18 GMT -5
Dave, Good news. I have ironed out all the problems except the meter is still DOA. All hums and noises are gone. Radio checks are superb. Will work on the meter problem. Can I manually test the meter by connecting a DMM across the pins? Question on the dim pot. This is the dual pot with the squelch. Does the dim part go all the way around, without stopping at the limits? Mine does. What did you do to eliminate your hum and noise issues? Yes you can manually test the meter with a DMM. It should show resistance. Actually a VOM would be better as the small amount of voltage present in the resistance modes will deflect the S meter to prove that it will respond. The dim pot should NOT rotate completely around. Looks like the stop is broken in that pot.
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Post by Deleted on Dec 22, 2010 9:20:55 GMT -5
I replaced several caps, mostly 10V variety. did all 3 on the mic amp PCB. Sound great.
Looks like I will need a new dual pot.
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Post by Deleted on Dec 22, 2010 19:40:09 GMT -5
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Post by Sandbagger on Dec 23, 2010 11:48:13 GMT -5
Is it possible to repair the "dim" pot? Yes, you can pull it apart and see if you could replace the broken stop. But chances are that unless you have "pot parts" handy, you might be better off just looking to replace it. As for the clarifier mod, yes, you don't have to replace the varactor diode unless you want super extended range. But just as a matter of note, when you eliminate R422 and run the low side of the clarifier pot to ground, you will pick up some extended range. But the center slot will be off and you will have to realign L's 16,17,and 18 for center slot again.
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Post by Deleted on Dec 28, 2010 0:07:40 GMT -5
Dave,
More progress. I removed the meter and loosened the screw to free it. My VOM pegged it. I hope pegging it didn't damage it.
I removed the dim pot, and disassembled it. The stop is there, and appears to be normal. It does not appear broken. Are you sure the dim pot is not supposed to turn all the way around without stopping?
Also, I want to upgrade the NB and detector with 1N5711 Shottky diodes. Let me know if you think that is a bad idea.
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Post by Sandbagger on Dec 28, 2010 10:46:38 GMT -5
Dave, More progress. I removed the meter and loosened the screw to free it. My VOM pegged it. I hope pegging it didn't damage it. I removed the dim pot, and disassembled it. The stop is there, and appears to be normal. It does not appear broken. Are you sure the dim pot is not supposed to turn all the way around without stopping? Also, I want to upgrade the NB and detector with 1N5711 Shottky diodes. Let me know if you think that is a bad idea. So the meter was just stuck? Looks like you might have fixed it. The dim pot does not rotate all the way around. When you're looking for the stop, make sure you're looking at the dim pot and not the squelch. The NB on that radio is very effective as is. Replacing the diodes might improve it, then again, it might screw it up. This is one of those cases where "if it works, don't mess with it".
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Post by Deleted on Dec 29, 2010 11:01:22 GMT -5
Dave,
Weird thing. Must be a typo in the Radio Shack service manual. I am doing a PLL alignment, and the parts to adjust the freq for L16, L17, L18 looks wrong.
L17 says TP3, yet L16 and L18 say TP1. I cannot measure anything at TP1. So I go back to TP3, and sure enough, all is good. Curious, I went to the CBtricks Cobra 146 page, and their service manual states TP3 for all those adjustments.
I just wanted to make sure I was not seeing things, and wanted to check with you.
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Post by Sandbagger on Dec 29, 2010 11:46:37 GMT -5
Dave, Weird thing. Must be a typo in the Radio Shack service manual. I am doing a PLL alignment, and the parts to adjust the freq for L16, L17, L18 looks wrong. L17 says TP3, yet L16 and L18 say TP1. I cannot measure anything at TP1. So I go back to TP3, and sure enough, all is good. Curious, I went to the CBtricks Cobra 146 page, and their service manual states TP3 for all those adjustments. I just wanted to make sure I was not seeing things, and wanted to check with you. Service manuals are written by humans. Humans make mistakes. I've found several mistakes in SAMs manuals over the years, and I got into a big argument with good ol Frank over a typo in another manual some years back. TP1 is in the noise blanker circuit so that can't be right. TP3 makes far more sense.
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Post by Night Ranger on Dec 30, 2010 8:43:14 GMT -5
Dave, Weird thing. Must be a typo in the Radio Shack service manual. I am doing a PLL alignment, and the parts to adjust the freq for L16, L17, L18 looks wrong. L17 says TP3, yet L16 and L18 say TP1. I cannot measure anything at TP1. So I go back to TP3, and sure enough, all is good. Curious, I went to the CBtricks Cobra 146 page, and their service manual states TP3 for all those adjustments. I just wanted to make sure I was not seeing things, and wanted to check with you. I have the service manual for a TRC-451. I'll look at it when I get home. It seems like I remember the USB/LSB adjustments being reversed in the service manual, but I could be confusing it with another service manual.
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Post by Deleted on Dec 30, 2010 8:46:17 GMT -5
The USB/LSB adjustments are reversed.
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Post by zman on Dec 30, 2010 16:34:24 GMT -5
Do a peak and tune and that radio will scream.
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Post by Deleted on Dec 30, 2010 20:45:24 GMT -5
I cannot get the LSB adjust to read 10.6975. I can only get it as far as 10.6955. Any ideas? All other adjustments fall right into place.
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Post by Sandbagger on Dec 30, 2010 21:35:39 GMT -5
I cannot get the LSB adjust to read 10.6975. I can only get it as far as 10.6955. Any ideas? All other adjustments fall right into place. The crystal is probably out of tolerance. As a quick bandaid fix, you could try lowering the value of C103 to 10pf or possibly lower if need be.
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Post by Deleted on Dec 30, 2010 22:48:59 GMT -5
I got it. Don't know if my freq counter was flukey. Great reports on AM. Both SSB appear to be on from my friend Icom 746. Will align receive tomorrow.
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Post by Deleted on Dec 31, 2010 19:21:22 GMT -5
OK guys. Many thanks to you. Alignment was fairly routine, once I figured out the errors. I left it stock, aside from an open clarifier. The modulation was set to slightly over 100%, with nothing clipped. Radio reports are great.
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Post by Sandbagger on Jan 1, 2011 1:15:47 GMT -5
OK guys. Many thanks to you. Alignment was fairly routine, once I figured out the errors. I left it stock, aside from an open clarifier. The modulation was set to slightly over 100%, with nothing clipped. Radio reports are great. The mod pot set at max is just over 100% and the audio is just wonderful. One of the smoothest sounding solid state rigs I have. The only mods I've done were the open clarifier, and I reassigned the dim pot to be variable carrier power on AM. Makes it easier to "dial-in" an amp......
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Post by Deleted on Jan 1, 2011 11:21:32 GMT -5
Dave,
Quick question on the S meter. It seems to be a swinging meteron RX. My TRC-455 seemed to be a average meter. The TRC-455 would show a firm signal with no swing on RX. The TRC-451 shows it swinging with the receiving modulation. Also, one of my locals comes in with typical audio, and no S reading. I am going to recalibrate the meter. 100uf at S9. Does yours behave the same way?
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Post by Sandbagger on Jan 1, 2011 15:09:53 GMT -5
Dave, Quick question on the S meter. It seems to be a swinging meteron RX. My TRC-455 seemed to be a average meter. The TRC-455 would show a firm signal with no swing on RX. The TRC-451 shows it swinging with the receiving modulation. Also, one of my locals comes in with typical audio, and no S reading. I am going to recalibrate the meter. 100uf at S9. Does yours behave the same way? Well, the meter on my TRC-451 is fairly typical of the Uniden-based radios. It's very loose on the lower end (a 3db change in signal will jump almost 2 "S" units) between S1 and S5. It starts to tighten up between S7 and S9. So people giving me low signals will show far more swing than those who are S7 or better. How is the receive on your radio? How low can you drop the generator and still hear a signal. Mine will go down to .1 uV and I can still hear it. I get S meter deflection before I hit 1 uV. I also set my S9 reading using 50 uV. I've seen some procedures that call for 50 uV and some that call for 100 uV. I'm not sure why there is a difference in "standard", but I chose 50 uV for my standard. It's unusual to have a radio show no swing on signals. Especially today with so many "super swing" stations out there. Most of my radios will show some additional deflection with modulation, the best are those which correctly discern backward and forward swing as appropriate. The worst is my SBE Console II which shows radical backswing for any signal with modulation. Someday, I'd like to see if I can correct that, but I don't have the time as of now. Sometimes you can dampen the meter movement by increasing the capacitor value in parallel with the meter.
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Post by Deleted on Jan 1, 2011 19:13:50 GMT -5
Dave,
This meter is weird. I will have to get back to you on if 1 uV deflects it. The meter itself might be bad. I think a standard Cobra 148 meter should work.
Anyway, I can hear down to .3 uV, and I seem to lose it at .2 uV. I am not sure if that is withing spec or not. But it appears it goes down to .2 uV.
Quick question. Is there a high impedance analog FET VOM that I can use to align the receive? This DMM fluctuation is driving me nuts. I purchased a VTVM from a hamfest, and sure enough it was no good.
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Post by Sandbagger on Jan 1, 2011 22:12:40 GMT -5
Dave, This meter is weird. I will have to get back to you on if 1 uV deflects it. The meter itself might be bad. I think a standard Cobra 148 meter should work. Anyway, I can hear down to .3 uV, and I seem to lose it at .2 uV. I am not sure if that is withing spec or not. But it appears it goes down to .2 uV. Quick question. Is there a high impedance analog FET VOM that I can use to align the receive? This DMM fluctuation is driving me nuts. I purchased a VTVM from a hamfest, and sure enough it was no good. You can use a scope, or you can just tune by ear or the S-meter. Just make sure to keep the signal level as low as you can and still be able to see a usable signal. If you are using an AC voltmeter from the audio output, a standard VOM will work. I like to use a scope right at the detector output. That way I can make sure there is no distortion from an improperly aligned IF.
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