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Replacing bi-polar capacitors Kenwood KR-5150

jpreza

jpreza

Active Member
I'm finishing up restoring a Kenwood KR-5150. Love those tusks!! I finally replaced the burned out bulbs and she's looking pretty.

Anyway, I noticed that the IF board (UA1224K3) has a couple of 3.3uF 25V marked as bi-polar capacitors. The parts description list of the service manual describes as "electrolytic tubular" capacitors, no different than the others. Before messing with the IF board capacitors, is it wise to replace these?

One other thing that's bugging me is the fine tune meter - the light is out but it actually works, as I can see the needle moving. I replaced the 33uF capacitor but it made no difference.

TIA....JP
 
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Those are likely to be bipolar electrolytic capacitors, not transistors. You can get something like the Nichicon ES series.
 
To answer your question, I avoid replacing items in tuners, as it might change the operations enough to require an alignment, and I’m not equipped to do that.

If the tuner is fine, leave them be. They get pretty light duty.
 
Semanon said:
To answer your question, I avoid replacing items in tuners, as it might change the operations enough to require an alignment, and I’m not equipped to do that.

If the tuner is fine, leave them be. They get pretty light duty.
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I don't have the necessary equipment either to do a tune alignment. I've heard that there are iPhone/Samsung apps that can be used but I haven't seen anyone do that or post about it on AK.
 
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Replacing the capacitors, resistors, transistors and diodes in a tuner circuit is perfectly ok... you just have to very careful

  • replace with exact matches
  • replace with lots of care (get help here if you don't know)
  • don't change the components in the frontend... as that will necessitate realignment

That said, avoid replacing or adjusting the variable capacitors and variable inductors... as that will likely necessitate realignment.

FM alignment requires quite a bit of extra, specialized gear... and great instructions or experience. "Just an app" will not do what you need done. Here are some links I've used in past if you care to dig in deeper:

 
dlucy said:
Replacing the capacitors, resistors, transistors and diodes in a tuner circuit is perfectly ok... you just have to very careful

  • replace with exact matches
  • replace with lots of care (get help here if you don't know)
  • don't change the components in the frontend... as that will necessitate realignment

That said, avoid replacing or adjusting the variable capacitors and variable inductors... as that will likely necessitate realignment.

FM alignment requires quite a bit of extra, specialized gear... and great instructions or experience. "Just an app" will not do what you need done. Here are some links I've used in past if you care to dig in deeper:

Click to expand...
Thanks dlucy for your input!

When you say "replace with exact matches" do you mean for example if it's a 47uF 25V, is it okay to replace with a 47uF 50V?

When you say "the frontend" I'm not sure what you mean by that. I'm somewhat of a newbie on the audio "slang" :rflmao:
 
jpreza said:
Thanks dlucy for your input!

When you say "replace with exact matches" do you mean for example if it's a 47uF 25V, is it okay to replace with a 47uF 50V?

When you say "the frontend" I'm not sure what you mean by that. I'm somewhat of a newbie on the audio "slang" :rflmao:
Click to expand...

Yes, 47 uF 25 V cap is the same capacitance as 47 uF 50 V. You've got it right.

What is the RF frontend? Wikipedia explains it (for my purposes) really well: https://en.wikipedia.org/wiki/RF_front_end

In your KR-5150, this is the "frontend":


Kenwood KR-5150 FM frontend.png

You can carefully replace the components in the frontend... following those guidelines above (remember, I'm no E.E.; just commenting from firsthand experience). Don't replace or adjust any of the variable or tunable components (e.g. CTnn), but the normal non-tunable components (e.g. Cann and Rann) are fine to replace... with exact matches.
 
dlucy said:
but the normal non-tunable components (e.g. Cann and Rann) are fine to replace... with exact matches.
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Very dangerous, the Front End is extremely sensitive to the smallest of capacitance changes. That coupled with the heat of soldering and the possibly slightly different size replacements and their placement, could trigger that dreaded re-alignment, of the Front End at least. In my opinion some of the Cbnn are safe to replace, but only some. ;)
 
I ended up "lifting" all the capacitors on the IF board to see if any of them were leaking. There was one, Cb35 47uF 16V, that was totally bulging at the bottom with yellow stuff coming out of it. I went ahead and replaced just this one. Afterwards, there is slight drifting in the stereo signal. To demonstrate, I picked up the strongest FM station around me. Whenever the fine tune meter is dead center, the stereo signal lights up, the tuning meter signal is around 3.5, but there is definitely distortion. If I move the tuning needle slightly to the left, the stereo signal bounces on and off, the tuning meter signal goes to 4.75-5, and there is no distortion, but the stereo separation is minimal. Any suggestions?

TIA...JP
 
this has done wonderful things on a few tuners on my bench

How to clean a tuner (analog)

1. Vacuum out all the dust you can from the interior. Don't touch the fins on the tuning cap! 2. Blow the dust out of the fins with compressed air. Don't touch the fins. 3. If you examine the tuner cap, you will see brass contacts at each point where the shaft passes through the metal housing...
audiokarma.org

i'd replace all the electrolytics on the tuner board personally.
 
jpreza said:
I ended up "lifting" all the capacitors on the IF board to see if any of them were leaking. There was one, Cb35 47uF 16V, that was totally bulging at the bottom with yellow stuff coming out of it. I went ahead and replaced just this one. Afterwards, there is slight drifting in the stereo signal. To demonstrate, I picked up the strongest FM station around me. Whenever the fine tune meter is dead center, the stereo signal lights up, the tuning meter signal is around 3.5, but there is definitely distortion. If I move the tuning needle slightly to the left, the stereo signal bounces on and off, the tuning meter signal goes to 4.75-5, and there is no distortion, but the stereo separation is minimal. Any suggestions?

TIA...JP
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Odd. Cb 35 seems to be part of the AM RF amp and should not impact FM. Did you note the problem before? Did you measure the new and old caps?

Suggestions…Put the old cap back? Check the installation to make sure it’s right? Take it to a shop for alignment? That’s the problem with tuner sections. Sometimes changes make no difference. Other times they go wonky.

Just a thought, The yellow stuff may have been glue, not electrolyte. Electrolyte discolors the board and IME is pretty clear and does not have a color. Was this stuff opaque and hard?
 
Semanon said:
Odd. Cb 35 seems to be part of the AM RF amp and should not impact FM. Did you note the problem before? Did you measure the new and old caps?

Suggestions…Put the old cap back? Check the installation to make sure it’s right? Take it to a shop for alignment? That’s the problem with tuner sections. Sometimes changes make no difference. Other times they go wonky.

Just a thought, The yellow stuff may have been glue, not electrolyte. Electrolyte discolors the board and IME is pretty clear and does not have a color. Was this stuff opaque and hard?
Click to expand...
It definitely wasn't glue. The bottom of the cap was completely exposed and it looked like a rocket, as if the bottom had opened up. I'm going to clean the fins and see if that helps.
 
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