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Post by Deleted on Jan 26, 2013 19:12:23 GMT -5
TRC-422A. I just got 5 "new" 10.240 crystals from a UK vendor and they are measuring 10.235 in circuit. I have 30 your old crystals that are closer in frequency. Am I screwed?
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Post by Night Ranger on Jan 26, 2013 22:42:07 GMT -5
I just got 5 "new" 10.240 crystals from a UK vendor and they are measuring 10.235 in circuit. I have 30 your old crystals that are closer in frequency. Am I screwed? Change the capacitance from one of the crystal leads to ground and you may be able to shift it back to 10.240 MHz. This is a schematic of a Realistic TRC-422a. www.cbtricks.com/radios/realistic/trc_422a/graphics/trc_422a_sch.jpg Find the 10.240 MHz crystal attached to pins 11 and 12 of IC1 (LC7130). Notice the capacitor C36 that goes from one leg of the 10.240 MHz crystal to ground. By changing the value of that capacitor you can alter the frequency of the crystal oscillator in the circuit. You can try the same thing in your circuit as well. If it does not have a capacitor to ground from one leg of the crystal then add one. You will have to experiment with different capacitor values to find the right one. You can also use a small trimmer capacitor to ground if your circuit does not already have one. Night Ranger |
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Post by Deleted on Jan 26, 2013 22:43:41 GMT -5
Will do, Mike.
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Post by Night Ranger on Jan 26, 2013 22:47:27 GMT -5
I updated the previous post after you responded. Night Ranger |
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Post by Deleted on Jan 27, 2013 17:00:19 GMT -5
OK. That worked. I aligned the RX and the RX audio sounds terrible. Sounds distorted. I removed the antenna and put in an audio signal threw the audio chain and seems pretty clean, so I want to rule out the audio chip.
I did not have this problem when I put it away many years ago. I recapped it and it appears the problem emerged. I used new caps. I am wondering if one of the caps was bad.
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Post by Night Ranger on Jan 27, 2013 18:16:14 GMT -5
OK. That worked. I aligned the RX and the RX audio sounds terrible. Sounds distorted. I removed the antenna and put in an audio signal threw the audio chain and seems pretty clean, so I want to rule out the audio chip. I did not have this problem when I put it away many years ago. I recapped it and it appears the problem emerged. I used new caps. I am wondering if one of the caps was bad. You'll probably need to walk the "IF" chain to find the bad part. If you have a shortwave receiver you can use it to sniff each stage of the receiver. If the IF frequencies are 10.695 MHz and 455 kHz then tune the receiver to each IF frequency and trace the circuit along the receiver chain. Change to the 2nd IF frequency once you hit the mixer stage for the second IF frequency. Be sure to use a small ceramic disc capacitor to block DC voltage from the radio you are testing back to the listening shortwave receiver. You may not even need to make a direct connection between the listening shortwave receiver and the radio you are testing as simply placing a coiled up insulated wire connected to the listening shortwave receiver next to each IF section may be able to sniff out the IF at that stage from the radio in question. The "sniff" method is preferred over the direct connection as it eliminates the possibility of damage to the listening shortwave receiver front end. Night Ranger |
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Sandbagger
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Post by Sandbagger on Jan 28, 2013 6:42:59 GMT -5
OK. That worked. I aligned the RX and the RX audio sounds terrible. Sounds distorted. I removed the antenna and put in an audio signal threw the audio chain and seems pretty clean, so I want to rule out the audio chip. I did not have this problem when I put it away many years ago. I recapped it and it appears the problem emerged. I used new caps. I am wondering if one of the caps was bad. What kind of radio is this? In most rigs the audio chip is shared on TX and RX, so if the TX audio is clean, then the problem is not in the chip. Distorted receive can occur if the I.F. is misaligned. I've run across radios where you can peak the receiver with an unmodulated signal for best meter strength/sensitivity, and then the audio sounds distorted. You have to align with a modulated signal for cleanest receive audio. Sometimes this results in a difference in sensitivity. If the difference is more than slight, it may mean that a crystal or mechanical I.F. filter has drifted off. |
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Post by Night Ranger on Jan 28, 2013 8:39:28 GMT -5
OK. That worked. I aligned the RX and the RX audio sounds terrible. Sounds distorted. I removed the antenna and put in an audio signal threw the audio chain and seems pretty clean, so I want to rule out the audio chip. I did not have this problem when I put it away many years ago. I recapped it and it appears the problem emerged. I used new caps. I am wondering if one of the caps was bad. What kind of radio is this? In most rigs the audio chip is shared on TX and RX, so if the TX audio is clean, then the problem is not in the chip. Distorted receive can occur if the I.F. is misaligned. I've run across radios where you can peak the receiver with an unmodulated signal for best meter strength/sensitivity, and then the audio sounds distorted. You have to align with a modulated signal for cleanest receive audio. Sometimes this results in a difference in sensitivity. If the difference is more than slight, it may mean that a crystal or mechanical I.F. filter has drifted off. Nice info. I've always used an modulated carrier to peak the IF chain. I'll have to switch to the modulated signal next time. Night Ranger |
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Post by Deleted on Jan 28, 2013 9:47:32 GMT -5
What kind of radio is this? In most rigs the audio chip is shared on TX and RX, so if the TX audio is clean, then the problem is not in the chip. Distorted receive can occur if the I.F. is misaligned. I've run across radios where you can peak the receiver with an unmodulated signal for best meter strength/sensitivity, and then the audio sounds distorted. You have to align with a modulated signal for cleanest receive audio. Sometimes this results in a difference in sensitivity. If the difference is more than slight, it may mean that a crystal or mechanical I.F. filter has drifted off. Nice info. I've always used an modulated carrier to peak the IF chain. I'll have to switch to the modulated signal next time. Night Ranger TRC-422A. Used a 1 KHz 30% signal. If the filter has drifted, what should I do? |
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Sandbagger
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Post by Sandbagger on Jan 28, 2013 11:27:16 GMT -5
Nice info. I've always used an modulated carrier to peak the IF chain. I'll have to switch to the modulated signal next time. Night Ranger TRC-422A. Used a 1 KHz 30% signal. If the filter has drifted, what should I do? If the filter is off, then replacing it is the best option. Best place to find them is in a "parts" radio. But try re-aligning the I.F. first for best clarity. If you can, kick the signal generator's modulation up to 90%. That way the distortion becomes much easier to see on a scope, or hear with your ears. |
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Post by Deleted on Jan 28, 2013 11:32:26 GMT -5
That little black box with murata?
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Post by Night Ranger on Jan 28, 2013 13:12:34 GMT -5
That little black box with murata? Probably. Do you have a shortwave receiver you can tune to the IF frequencies and walk the receiver IF chain with? If so that will say you alot of guess work, and alot of part swapping. Night Ranger |
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Post by Deleted on Jan 28, 2013 17:50:55 GMT -5
I do not. I had one and sold it.
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Sandbagger
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Post by Sandbagger on Jan 28, 2013 18:08:38 GMT -5
That little black box with murata? That would be it.......  |
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Post by Deleted on Jan 28, 2013 19:44:36 GMT -5
Well, it appears something drifted. TX audio was reported good. The very string signals distort. I tweaked T7 and it appeared to improve dramatically. I can retune for a different IF of like 456 or so.
Mouser has these filters. Would you know what the impedance is on these?
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Post by Sandbagger on Jan 28, 2013 20:50:51 GMT -5
Well, it appears something drifted. TX audio was reported good. The very string signals distort. I tweaked T7 and it appeared to improve dramatically. I can retune for a different IF of like 456 or so. Mouser has these filters. Would you know what the impedance is on these? I do not know the exact specs on the filter, that's why I suggested scavenging one from a similar radio. If there is a part number on the filter itself, you might be able to cross it that way. Also, make sure that your first L.O. and 2nd L.O are both on-frequency. If those are off, then the conversion will be too. You can test the 455 khz I.F by simply injecting a 455 khz signal into the output of the 2nd mixer and see if you can tune those cans for the proper frequency without distortion. If those work ok, then you have an issue with conversion frequencies. But If it's still "off" when you try it with the 455 Khz signal,then you have an issue with the filter or some other part of the 455 Khz I.F. chain. |
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Post by Marc on Jan 29, 2013 11:36:13 GMT -5
Most of them are the 455h or 455ht 2000 ohm impedance.
The HT filter has a steeper skirt.
marc
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Post by Night Ranger on Jan 29, 2013 13:26:11 GMT -5
Most of them are the 455h or 455ht 2000 ohm impedance. The HT filter has a steeper skirt. marc I've only see one radio that had the 455 kHz filter go bad, and that was after the radio was submerged under water for several days after a pipe burst in the basement and the home owner's were out of town. My guess is the problem lies somewhere else. Night Ranger |
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Post by Marc on Jan 29, 2013 15:49:19 GMT -5
No they don't go out very often. I have replaced only one because of damage one leg was broken.
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Post by Deleted on Jan 29, 2013 17:06:47 GMT -5
You guys may be right. I just noticed that my ANL virtually shuts off receive audio when switched on. You can barely hear audio with the volume all that way up. When it is out, the receive volume sounds normal.
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Post by Sandbagger on Jan 29, 2013 19:05:48 GMT -5
You guys may be right. I just noticed that my ANL virtually shuts off receive audio when switched on. You can barely hear audio with the volume all that way up. When it is out, the receive volume sounds normal. Then you may have bad detector diodes. If they're off, they might clip your detected audio and introduce distortion. The ANL clipper diodes reduce hash noise be deliberately clipping the noise peaks. This action results in a bit of audio distortion (which is why I like to run with the ANL off). But if the audio is nearly cut completely off when the ANL is on, then something is off in that circuit. If not the ANL diode (or in the case of this radio a transistor), check for the presence of 10V electrolytics in the nearby circuit. Those are trouble in any radio. |
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Post by Deleted on Jan 29, 2013 19:17:35 GMT -5
Way ahead of you. The caps were all replaced. I swapped the detector diode. No change. I am thinking the quad op amp.
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Post by Sandbagger on Jan 30, 2013 8:53:13 GMT -5
Way ahead of you. The caps were all replaced. I swapped the detector diode. No change. I am thinking the quad op amp. That should be easy to test. If you inject a pure audio sinewave, like a 1khz tone, right after the detector, and into the input of the op-amp, and the signal is distorted, then you know your problem is in the audio chain. If it's clean at that point, we're back to the I.F. / detector/ANL stage. You did say before that you were able to improve it by tuning one of the I.F. cans. That's why I keep thinking that the problem is there. As another thought, have you checked the AGC action? If the distortion only occurs with very strong signals, this could be a sign of a non-working AGC, especially considering that the ANL transistor ties in with it, and you said that activating the ANL killed most of your audio. If your S-meter or squelch is not working properly, that's another clue. |
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Post by Deleted on Jan 31, 2013 20:02:13 GMT -5
Fixed it!
While recapping the electrolytics, I had one of those multi-lead solder pads where I had a meeting of like 5 components. One of those was C31, a Mylar cap. The lead slipped below the solder pad and was not connecting. Having you guys tell me to poke around the detector with a signal, helped me find it. While injecting the signal and moving grabbers around, I heard the signal change pitches. I then started to poke around with a metal screwdriver and saw sparks (OK, that is a joke). I really poked with a plastic tuning tool. I hit C31, and it changed pitch and sounded distorted. I thought it was bad, so when I went to remove it, I saw it was not in the pad!
I have my childhood radio up and running ! Thanks so much to everyone.
Mike (Night Ranger), if you can do me a favor and take a cover off and tell me the board values of C63 and C65. Mine had a 330 and 100, but the schematic should 470 and 47.
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Post by cbrown on Feb 1, 2013 9:30:34 GMT -5
Glad you got it working!
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Sandbagger
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Post by Sandbagger on Feb 1, 2013 15:46:33 GMT -5
Fixed it! While recapping the electrolytics, I had one of those multi-lead solder pads where I had a meeting of like 5 components. One of those was C31, a Mylar cap. The lead slipped below the solder pad and was not connecting. Having you guys tell me to poke around the detector with a signal, helped me find it. While injecting the signal and moving grabbers around, I heard the signal change pitches. I then started to poke around with a metal screwdriver and saw sparks (OK, that is a joke). I really poked with a plastic tuning tool. I hit C31, and it changed pitch and sounded distorted. I thought it was bad, so when I went to remove it, I saw it was not in the pad! I have my childhood radio up and running ! Thanks so much to everyone. Mike (Night Ranger), if you can do me a favor and take a cover off and tell me the board values of C63 and C66. Mine had a 330 and 100, but the schematic should 470 and 47. Somehow I knew it would come down to caps........ Glad to hear you got it working.... |
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Post by Deleted on Feb 1, 2013 17:17:46 GMT -5
Dave,
The procedure for RX alignment asks to adjust the T9 output for the local oscillator to maximum. But it lists no tests point. Just says to use 20 mV as reference. Should I measure the output on the base of Q3?
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Post by Night Ranger on Feb 1, 2013 18:13:07 GMT -5
Fixed it! While recapping the electrolytics, I had one of those multi-lead solder pads where I had a meeting of like 5 components. One of those was C31, a Mylar cap. The lead slipped below the solder pad and was not connecting. Having you guys tell me to poke around the detector with a signal, helped me find it. While injecting the signal and moving grabbers around, I heard the signal change pitches. I then started to poke around with a metal screwdriver and saw sparks (OK, that is a joke). I really poked with a plastic tuning tool. I hit C31, and it changed pitch and sounded distorted. I thought it was bad, so when I went to remove it, I saw it was not in the pad! I have my childhood radio up and running ! Thanks so much to everyone. Mike (Night Ranger), if you can do me a favor and take a cover off and tell me the board values of C63 and C65. Mine had a 330 and 100, but the schematic should 470 and 47. Those capacitors are connected to the audio chip. They probably just affect the tone. I can look the next time I am by the radio. Night Ranger |
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Sandbagger
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Post by Sandbagger on Feb 1, 2013 22:59:27 GMT -5
Dave, The procedure for RX alignment asks to adjust the T9 output for the local oscillator to maximum. But it lists no tests point. Just says to use 20 mV as reference. Should I measure the output on the base of Q3? That would be as good a place as any. Just make sure you have a high impedance probe. |
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Post by 2600 on Feb 2, 2013 17:58:06 GMT -5
Um, too lazy to look at the schemo right now.
Look for a small-value electrolytic capacitor in the ANL circuit. If this radio has one, it could cause this trouble if it fails.
73
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