| Author |
Message |
    
Scarecrow
Junior Member
Username: Scarecrow
Post Number: 13
Registered: 1-2021
| | Posted on Saturday, January 21, 2023 - 11:48 pm: | 
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I have a PC 66 XL that has had R38 and D9 clipped by previous owner. I think D9 is clipped to bypass VR5, but i would like to know why R38 was clipped.
Any help is greatly appreciated, TY |
Ke0koy
Member
Username: Ke0koy
Post Number: 57
Registered: 12-2018
| | Posted on Saturday, January 28, 2023 - 2:17 am: |
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I am looking at the PC66 schematic, not sure if it is the same as the PC66XL.
If the schematics are the same, cutting D9 disables the ALC.
The schematic I have is very poor resolution. What resistor is R38? Is that the one between the 54MHz trap and the antenna jack (that provides DC ground for static dissipation and shouldn't have been cut), or are you talking about what looks like R58 between D9 and the base of Q14 (which is part of an RC filter to smooth the negative ALC voltage that is no longer present and therefore shouldn't have been cut either)? |
Scarecrow
Junior Member
Username: Scarecrow
Post Number: 14
Registered: 1-2021
| | Posted on Saturday, January 28, 2023 - 11:28 am: |
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R38 is located in the rear of the the board, in between the L20 trim pot and the antenna jack/lead.
Hope that makes sense. lol
I dropped a tiny amount of solder on it to reconnect it.
Thank you very much for your time and response. |
Ke0koy
Member
Username: Ke0koy
Post Number: 58
Registered: 12-2018
| | Posted on Tuesday, January 31, 2023 - 12:41 am: |
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Yep, that resistor is the one for dissipating static buildup. Antennas blowing in the wind can quickly pick up a charge if there is no DC path to ground. |
Scarecrow
Junior Member
Username: Scarecrow
Post Number: 15
Registered: 1-2021
| | Posted on Tuesday, January 31, 2023 - 10:44 pm: |
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Thank you very much for the help and education.
I'm just one of those guys that takes a look at radios that have quit on people, not a tech by any stretch, so your guidance is greatly appreciated. |
Ke0koy
Member
Username: Ke0koy
Post Number: 59
Registered: 12-2018
| | Posted on Thursday, February 02, 2023 - 2:34 am: |
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Same here. I like to think that I am starting to understand this stuff, but it's slow going and I learn something new every day.
Right now I am working on a Royce 1-621 that a friend bought online as "untested". I tracked the problem down to the PLL, but uunfortunately, nobody has a schematic for it (or nobody is willing to share it). So, I pulled it out of the radio and spent the better part of today putting the parts and the traces on the same piece of paper just as they are on the board (112 comonents worth if I remember correctly). Now that I have a crude schematic for it, I have to turn that into a neat looking schematic (probably another half day at my pace). I was going to send this thing back to it's owner, but I figured it would be a great learning tool with it's PLL unit being such a mystery.
Last week I learned how to match the low impedance of final transistors to 50ohm with a smith chart. I've been messing with smith charts for a while, but I fell down the rabbit hole because Lou Franklins book "Understanding and Repairing CB radios" stated that the L match and half wave filter are calculated seperately, but then he shows an example where that strategy was clearly not followed. A week before that I learned how to tweak the components in a simplpe oscillator circuit (by using my VNA to look into the base) to adjust the range of frequencies with negative resistance for reliable startup at overtones. That was on my bucket list for years.
I'll just keep pushing forward until the day comes I feel confident enough to print CB repair business cards. I just want to be absolutely sure that when I do, I am not one of those chop shops that screw stuff up. I want fixing radios to be my retirement plan... |
Scarecrow
Junior Member
Username: Scarecrow
Post Number: 16
Registered: 1-2021
| | Posted on Thursday, February 02, 2023 - 11:04 pm: |
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Wow. Way above my pay grade. Lol
Have fun with your efforts to refine the craft of electronic repair, I'll just keep trying to avoid starting a component or circuit fire on my next experiment.
Thanks again, and I'll keep looking for your posts |
