Publikované v: Technique
Hello
I have an older Kenwood 850 TRX and I plan to replace all
electrolytics. Most (especially smaller capacities) I have new tantalum capacitors. The question is whether it is possible to replace them for electrolytics. It mainly concerns the RF and IF boards, possibly the microphone part. Thank you for your response.
Everything is possible, but it would definitely need a schematic to determine what that electrolytic is actually for.
Tantal is basically an electrolytic but has some 'enhanced' properties. Better capacity per cm3, lower leakage. But they also have worse properties. During reverse polarity, they get damaged more than the classic ones, and especially when exceeding the rated voltage, they tend to rupture or explode sooner.
Reverse polarity could only be managed by replacing the electrolytics used for filtering voltages or managing operating points where there is a clear DC component, and certainly not to use them when they are used, for example, to separate stages where an AC component is transmitted or it is not clear if it could appear there.
Exceeding the rated values can only be maintained if you use tantalum at a voltage with sufficient margin.
If it only concerns filter capacitors and you are willing to invest in a more expensive component than actually needed, then I see no problem.
Otherwise, I don't understand why everything for tantal. They are mainly used for energy-efficient devices where minimal dimensions and mainly minimal energy requirements for the device are needed. Personally, I would replace classic with classic and wouldn't put tantal there just because someone said they are 'better' than classic electrolytics.
Thanks for the reply
Some I have already replaced with electrolytes and the old ones were even below 50% value. The worst part is that even the new 10uF electrolyte measures 8uF after testing and it hasn't even been in operation yet. Even though it's not critical, I wouldn't want to do this again in a few years.
In the trx, I think there are no voltages higher than the power supply of 14v except for the output stage. Tantalums are rated at 25 and 35v in values from 1 to 100uF. Overvoltage is not a concern and I assume that most are filtering, some coupling between stages. Overall, there are 113 of them, so it won't be a joke.
One seller of the kit on eBay states that after re-capping with electrolytes, no adjustments are needed except for the VOX:
“There is no retuning of the radio required as the capacitors being changed are not RF related. Minor adjustment of the VOX controls may be required when new capacitors are installed.”
but I will set it again according to the manual.
As for the price, it is a clearance sale for the same or better price than the electrolytes.
So I don't know, try to advise.
This is how Russian televisions Šilelis or Elektronika used to be repaired. If the radio works, there is no point in changing the electrolytes because 'Western' electrolytes are definitely better than Eastern ones. One should look for a fault or a reason for such an action.
I looked at what kind of radio it is, and I almost flipped over that operation. And that's one of the reasons why everyone should introduce themselves under their nickname in this forum.
As an example, I will mention my experience from 1961 when 'EXPERTS' went to the TV repair shop where we had a tube tester and brought 16 tubes for testing. The fee for testing one piece was 1 Kčs, which is about 33 cents today. Of course, I asked about the fault and only measured the bottles that were connected in the fault circuit.
In conclusion, you need to stop thinking about yourself and see if there is a radio club in the area that is still functioning, or a radio amateur who would advise on the basic steps. After all, it's total bullshit to start replacing ALL electrolytes. Even if it succeeds, there is a risk of damage to the circuit boards.
If there is a defect, take it to the service and it will be cheaper, or give me the radio and I will thank you.
I understood it more as modernization (or better written as an attempt to extend electrical longevity).
If you were to go into it, definitely don't do it all at once. Replace 5 pieces and test functionality. It will be easier to find the problem if something goes wrong.
Measuring capacitance is not that rosy. The classic has a tolerance of +/-20% without problems. So having 8uF instead of 10uF is completely normal. The second issue is the measurement itself. You certainly won't measure electrolytic capacitors accurately with a DMM because the principle of measurement simply doesn't allow it. Also, you measure at a certain voltage, temperature, and that's another problem. Otherwise, an electrolytic (if it's new and hasn't been used) needs to be formatted (especially larger capacitances) and measured before installation. It's possible that you install an electrolytic and it charges suddenly in the circuit and boom, the capacitance drops.
Personally, I wouldn't go into it. If the benefit is only that modernization, then it’s not worth the price of the problems that may arise. If there's a problem in the form of ripple (for example, at TX), then just replace the filtering in that specific circuit, and whether you use tantalum or classic is up to you (provided you follow the conditions from my previous post).
When something breaks over time, you only replace the faulty component.
If you dare, go for it. One learns best from one's own mistakes, even if it sometimes costs a fortune.
I replaced the electrolytes in the TS850 on the DDS board. Out of ten replaced, 8 were completely without capacitance. The main reason for the replacement was that some leaked electrolytic and started to destroy the PCB. Then the frequency started to jump during transmission and other delicacies. On the Repair page about TS850 (http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=14552)
there's nothing about this problem, but somewhere I googled that you need to change electrolytics if the original ones have blue markings. Black marked ones are OK.
Otherwise, the replacement is no walk in the park, and I wouldn't attempt it at all without a hot air station. Desoldering the original electrolytics with a contact soldering iron without damaging the PCB is, in my opinion, impossible. They are soldered onto large copper areas, not from the side, but from underneath.
As a replacement, I put the same, but quality SMD types there. There is probably no room for saving here.
73 Petr OK1AYU
Thank you for the responses and greetings to Dusana CVV (Patince2001)
The previous owner was a tough user. Replacing the electrolytics after 17 years of hard operation certainly won't hurt. The radio has some minor issues: AGC occasionally flies, the ALC value changes slightly with heating, and when turning the antenna on the rotator, the signal drops on reception for about 2 seconds and you need to retune the tuner to the new position. (Could it be that the tuner has an RX mod done?) Also, the microphone input needs a lot of corrections from an external equalizer to get the modulation as it should be.
I once had it disassembled when I changed the swollen electrolytic on the IF board. It's a bit labor-intensive, but the TRX is made well. I plan to do it gradually by boards.
Since I certainly do not plan to buy a new 'entry-level' radio, I am trying to get the radio into decent condition, which I think it deserves.
Total investment of 8 euros for Jamicon 105C electrolytics and tantalum.
for AYU:
I have successfully replaced those SMD electrolytics for about a year. Mine also had blue printing and it was already at the eleventh hour. Moreover, I put adhesive heatsinks 2x2cm on the DDS chips. They are used on frames in graphics cards. I still have older DDSs YM6631, but so far they are working without problems.
please tell me, what kind of forum is this?
just Anonymous, xxl, datam, sabados, and similar...
I thought this was a radio amateur forum where everyone has their own nickname and logs in with it. So that everyone knows who they are communicating with.
Don't be offended, but on the forum CQ.SK it reminds me of chatter on CB - from
Pepa from the depot and not as it is grandly called here: European HAM portal.
I took the liberty of putting my invented name too, what it can probably bear.
sincerely Anonymous XXXL
First of all, unlike someone, I apologize for the off-topic but I must respond. What if that Pepa from the depot has more experience and knowledge than someone who has a brand? I've been on this forum for 3 days and there's so much negativity towards CB and the public that, although they don't have a license, they are interested in the topic that it must make a normal person sick. If this is a closed forum, then sorry for the intrusion into privacy.
two posts for consideration from our OMs
-the first advises him to take it to service, or give him a radio
😆
-the second one moralizes and is bothered that the nickname on the forum and the brand on the label are not the same, as is usually the case. The use and publication of personal and easily accessible information on the internet is still a personal matter for everyone. Even if it may not be polite, it should be respected!
😳
Such tuned posts only evoke unnecessary emotions. It probably needs more understanding and HAMSPIRIT.
73 Your ERROR
@datam wrote:
What if that Pepa from the depot has more experience and knowledge than someone who has a brand?
If this is a closed forum, then sorry for the intrusion into privacy.
ad 2.) The forum is not closed at all, so welcome to this forum and present your thoughts. The admin allows everything and everyone.
sincerely, your Pepa from the depot alias Fero from Dolná Horná
I surfed a bit, good article about elyts:
http://www.aldax.cz/index.php?tab=3&myordnum=&userid=&show=elyty
evaluation of the quality of elyts:
http://forum.audioweb.cz/viewtopic.php?pid=187845
They evaluate Jamicons there as junk. Hi
I did some measurements:
100u Jamicon has 80u, some have 78u
100u tantal has 98u
47u elyt Panasonic has 44u
Even though it is within tolerance and there will certainly be errors in the measurements, I will go through the schematic and where possible I will install tantalums.
I would be really careful with that replacement for tantalums, they are not suitable to be placed everywhere. From my more than 20 years of experience with repairs, I pay special attention to them! Usually, it has cost me quite a lot of effort and there was a faulty tantalum, it never had reduced capacity, but leakage and especially short circuit!
Device at 5V, capacitor at 25V and a pure short circuit, a very common situation!
When changing, it is better to use quality elyts. A good helper is to measure ESR
with this http://www.zajic.cz/esr/esr.htm , it is not an all-powerful tool, you have to know a bit where to measure what. When repairing TRX, it is an investment, I think acceptable.
you 73! Ruda OK1FDY
Thank you for the info, I take it into account.
If changing, then rather for quality electrolytes.
The problem is precisely that – quality. Costs are cut everywhere and then it looks like this. Manufacturers guarantee electrolytes a lifespan of 1000 hours, the better ones 3000.