#38 Icom IC 745 part 2 PLL repair and 2nd LO upgrade
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- Опубликовано: 28 авг 2024
- I decided to post this coming weekends video a bit early for some rest and relaxation.
In this video we finally have our parts to repair the VCO trimmers on the PLL board. We also will upgrade the 2nd local oscillator board to help the stability of this fine unit.
Parts needed for this repair:
4610000100 (6pf) 2 pieces.
4610000110 (12pf) 3 pieces.
24pf NPO disk capacitor 1 piece.
My website
gokarters.com/s...
I can't thank you enough for posting these IC-745 videos, Buddy. Our club has two of these great radios in its collection. One already has the RAM board failure (so the radio is somewhat of a brick), and other is exhibiting signs of the trimmer cap failure. I started troubleshooting the first radio back in October of last year but other projects got in the way so it was pushed aside. Since then, your greatly informative videos have appeared and have given me the encouragement to bring both of the IC-745s back to life. Hopefully you'll be uploading the RAM Board Replacement video shortly. Can't wait to see it. Best 73s. Aaron
+OldHamRadio Thanks Aaron for that wonderful comment. Those ram boards can be a pain. I am trying to put something together that is more modern and can be created in a lower skill requirement. It is taking a while to develop but maybe want be too far down the road. Thanks for watching and stay tuned.
The ground on the board is a large common area in between each set of capacitors. You state the flat is the rotor and should go to ground but you installed the flats to the outside. The ROUND side is the rotor! The INSIDE edges of the board is where ground is. I am doing an IC-751A and it is built in the VCO basically the same as your 745, even the capacitors are labeled the same C numbers! You DID install them correctly but state the flat side is the rotor when the ROUND side is the rotor. Hard to believe nobody has commented on this. 73, Dan W7RF
Icom used the same circuit topology on their IC-740's through the IC-765's, that is, if you look closely at the schematics such as in the PLL boards, they are nearly identical. I have two IC-745's and one IC-765, still terrific radios.
2 in one day bonus thanks again for the fantastic videos always interesting to watch. one of my hobbies is electronics and watching these videos pushed me to get my ham license not to long ago. (oct,2015) 73's Noah AC9MS
+preludelinux Thanks for the kind words Noah. If we had tools like RUclips when I was growing up imagine how simple things would had been. Just doing my part to help others. Electronics is a fun hobby. 73 Buddy
One other thing in the IC-745 to check is R1 on the little regulator board. The R1 resistor changes value and the +8 VDC supply voltage will drift. Change out that resistor maybe with a 1/2 watt size. The IC-745 will do strange things when that 8 volt supply is wrong. Spent 11 at Icom America doing technical support for their products. Been gone for 15 years so cannot remember the value of R1 but it was accurate on the schematic.
Gary
Thanks for that tip Gary. Always helps to know these things.
A very informative way of modifying and improving on the current design. It is clear that you and Paul think alike when it comes to repairs and improving on the manufactures designs, "well done"
+John Cunningham Thank you John. That was a very nice comment. Most id just practical thinking really. Always several ways to do things, the issue is finding the correct way. Then again if you are building something that you want to fail then that is what this radio is like. Paul is awesome, his creativity and knowledge is mind blowing. Another person mentioned not long ago that he would love to see Paul and myself tackle a project together.
I think that would be an excellent idea; when you have two minds working together there is no telling what will come of it. But, as you said there is a lot of ways to approach how you tackle repairs, especially very difficult ones. Electronic repairs is a craft that few people possess, you and Paul are in that category.
I could watch you all day, thanks Buddy
Hey Buddy ,great job can not wait till you get back on the kenwood 940 ,got one with same problem,driving me nuts thanks for all your hard work
+joel hall Thanks joel. Think I am going to have to call a priest to perform an exorcism on this one. Naw, we will get it...
Great upgrades Buddy! I have been working on a video (for too long now) that almost echo's your modifications, but in a different receiver. It's nice to see the parallel thought pattern. I would have done those mods the exact same way you did.
Take care!
+Mr Carlson's Lab Thanks for the conformation Paul. After looking that circuit over I was like what were they thinking? Way too much tuning and not enough fixed capacitance. Thanks for stopping in my friend. Lots to catch up on and your tech tip video to watch tonight.
Don't ya just hate it when the new parts bag has stuff missing..
Nice video Buddy
Cheers
John
+orbiter8 (John) Hi John, Yes I hate it when suppliers toy with me like this. Sort of ruined my weekend plans. How it goes at times. Thanks for stopping in my friend.
I just realized we're 40 miles apart! I'd love to hang out and learn some tips sometime. 73 de N4RMT
+ShooterReady Now that is pretty cool. I see you are in Elm city, Perhaps one week end we can get together.
Another great video Buddy ! Always this little crappy plastic caps.. Had a lot of those radios with vario probs... Take care 73
+TRXBench Hi Peter and thanks my friend. I see you notice it seems to always be capacitor problems also. Hard to use plastic and capacitor in the same sentence because we can see failure. Some company penny pinchers I guess. Thanks again Peter.
Great video good repair very good
I see a spare fuse taped to in line fuse holder I would worry about heat from radio making tape soft and drop fuse on PCB and cause proplem
+DENNIS N Thanks Dennis. Yes, that fuse there has to go. Good point!
Thanks so much for these videos! I don't understand how the trimmer and parallel capacitor values relate to stability. Why is the new combination preferable to the original?
Also, I have a 745 that gets very unstable (+/- 1kHz on 7MHz) after being on for a while. Do you think the 2nd LO could be the culprit?
The old trimmers are made out of plastic. The new trimmers are made from ceramic. Over time plastic moves around, warps and you no longer have a stable trimmer. Your problem sounds just as this.
@@TheRadioShop right, I'm wondering about c5 in the LO. Why is a larger fixed capacitor and smaller trimmer more stable?
Buddy - I had a heck of a time removing the RF shield, which was heavily soldered onto the board. How did you do this?
Mark, I use hot air with a very small nozzle. Works great.
I like that you make a series of it. Some people put so many issues in the video that i can not remember where i saw it. Good job. It's to bad that some people write (stamp) there call into the radio. You don't do that with your car? Oke keep the series coming. Is putting the crystal case to ground always a good thing or are there exeptions. I see it somtimes in radio's but not always. I see you next time. Best 73
+FEY Thank FEY. I like doing the series parts. Much easier on folks. Like a good tv show, always goes off right before the best part :) And I really hate seeing call signs or any marking in units. That is why the put serial numbers on them. No two are a like. Some old vintage stuff is ok. Tells a story. As far as grounding the crystal, well that depends on the circuit it is in. In the 745 we want to keep unwanted signals from entering the oscillator. As you know all the crystal is a piece of quartz suspended by two clips with a can over it and the bottom is just a holder. We also want to keep stray capacitance off. All done by a simple ground. Another by-product is this also secures the crystal case from vibration and snapping off at the base. See you in the next :)
Buddy do the 745 and the 751A share the same PLL board!?
nice video :)
+DJ Caverna Haroldo Bradaschia Neto Thank you very much sir.
Why they use 10v caps on a 16v circuit. I use larger when there is room.
Nice job Buddy. Tying the crystal down reminds me of a similar fix we used to do for the Drake twins VFO adding a mechanical flexible that really helped out on stability. Real radios glow in the dark! 73 - Dino KL0S
+Dino Papas Thanks Dino. One day I will own another Drake radio. Just have to find one. Would love to have a set of Drake twins. Wonderful AM rigs. But will take any Drake I can get. Grounding that crystal will do a lot of good there. Thanks for stopping by my friend.
Good Stuff
+S Robins Thank you Sue. Very glad you approve. I know you know these radio fairly well.
when you set the vco, do you ever have a problem like you can't reach the voltage listed?
I got a 765 and I can't get 6.5 volts on 2 trimmers. I can only get 5.8 and 6.3 on another, the other 2 are 6.5. (this is following correct procedure, and frequencies listed.)
thanks
Hi, Yes common problem. If the trimmers are the plastic ones then they need to be changed to ceramic replacements. C11, C20, C29, and C37. The plastic ones change in value over time. Don't forget the wax they used on some of these rigs becomes contaminated and needs to be removed and cleaned up. Make sure C226 is adjusted correctly. Also inspect the LPL board for cracked and dry solder connections. This is notorious on these. Hope some of this helps.
Thank You for posting this repair video! I am going to wait until i see the complete series of 745 vids before tearing into my 745. I don't have a reliable way to align my 745 here, but maybe something will work out later down the line. Thanks Again!
de kc5ngx
+jstrunck Thanks for watching. I will post another series on this probably next week. Depends on the work load here. I usually use a scope to align the VCO trimmers. I am sure we can find a different way.
+The Radio Shop Might be able to come up with a loaner Tektronix 465b oscilloscope.
+jstrunck Now that will work!
+The Radio Shop Excellent!
excellent video, love your work!
73
+su pyrow As always thanks my friend. You know this is easy ;)
+The Radio Shop yup... im shopping for a camera right now, cant afford the one you have, have to feed the family first.
I understand that bro. I like a new one also. Not that anything is wrong with what I have, just want more flexibility.
+The Radio Shop having trouble deciding whether i want to buy a non working camera and repair it or buy working... kind of cherry picking the best broken camera i can. lol
+The Radio Shop ohh im thinking of getting fishing line and a drop of krazy glue for the dial cord any suggestions?
Just wondering if you have had a chance to work on the Icom ic745? I still have my ic 745 here. I may just send it to you for a going over (yep..., vco trimmers crapping out) when time permits. It is a backup to my sr8t. No biggie. May use it hf mobile one day.
Thanks for all you do, and have done over the years. I am sure others feel the same way also.
John
KC5NGX
Hi John. Thanks for the kind words. If you like, order the trimmers and ship it to me. If you are not in a big hurry. It is a simple fix.
Thanks a lot for the great video!
So I try to get the trim capacitors 6pF and 12pF.....unfortunately without success (via Icon or dealer both negativ)
Can you give me a procurement address or help, where i can get the parts ? 73 DL9MEM Robert
Mine came from California Icom center. I will see if I can find the info
@@TheRadioShop Hello Buddy - do you have an adress for me?
why not try coating those variable caps in wax and see if that does the job first?
Icom actually did that in later production. The wax would help with microphonics. But it brought on other issues with the PLL circuit due to contamination. The wax then had to be removed. But in all once those plastic trimmers go bad thre is no reviving them. As the plastic ages the rotor becomes loose.
@@TheRadioShop I just bought one last night at auction. I hope I dont have to do that job. Removing that shield from the bottom is a real bear im sure. I dont have a vacuum desoldering tool which is what that requires.. My R71A has no stability problems and I think the circuitry is very similar no:?
Thanks for the videos btw, Most useful and enjoyabke
Another great video Buddy ! Always this little crappy plastic caps.. Had a lot of those radios with vario probs... Take care 73
+TRXBench Twice is nice :) he he
+The Radio Shop did not know if you noticed but there were two identical post from you. RUclips does strange things at times
+The Radio Shop Ja, I have seen it after you answered... You are right sometimes it is funny.. all the best and 73