having a "Recapping Emergency"

[seadzz]

I am in the middle of recapping my tuner....actually about 3/4 done and I have reached the dreaded situation where the part on the PCB does not match the value called out on the schematic. The drawing shows a 3.3uf 50V electrolytic but the part now in my hand is a 6.8uf 50V...what to do...what to do??

Half of me says put a 6.8uf back in there but the other half says match the drawing and insert a 3.3

Thoughts?


sdz

 

[drspiff]

go with the board. You know it was working before with the 6.8uf in there. But all this is moot if you have detected that someone has walked this way before you.

 

[rulerboyz]

Last time something like this got brought up I believe someone said something to the effect of: "trust the original circuit board layout first, the schematic second." 3.3uf is a common value for tuner sections that I see frequently. Someone like Echo Wars would be able to answer for sure by saying something surprising like: "either 3.3uf or 6.8, it doesn't make a difference"...just kidding.

 

[Lefty]

I agree, go with what you found on the board. Many times models had changes made during their manufacturing run and the service manual you have may not be the corresponding one or an addendum was added that was never republished in the service manual.

Lefty

 

[seadzz]

Thanks guys, thats exactly what I felt too. The attached file shows the circuit. Looks to be some sort os oscillator so if it worked with a 6.8 in there it will stay that way.

Goes to show that the Japanese are not perfect.

sdz

 

[pustelniakr]

It's a pain in the neck, but, set the unit to the side, and order the right part. If you are recapping, and you don't replace that one, and it is the only one you didn't replace, you will always have a pea under your mattress.

To minimize this kind of problem, I always order a couple more of any particular cap, than I actually need. In that way, as I go along, my "on-hand" inventory of caps increases. I cannot tell you how many times I have had to go to the well for a part that was different than what was on the schematic or parts list. Sometimes those 2 do not even match. I have actually encountered units where the part in the board, schematic, and parts list all reflect different parts. The Toshiba power amp I just recapped, gave me a gotcha, in that I ordered the right value and voltage, but the part turned out to be a bipolar 'lytic'. Dang! However, I just happened to have a couple bi-polars in just that value and voltage in my "on-hand" stock, form my work on PL-630 turntables so I did not have to go order the one cap I needed to finish the job.

Rich P

Left is right. Go with the board, unless there is evidence of "other" hands in there, on that particular cap.

Rich P

 

[lorne]

Rich P. wrote:

The Toshiba power amp I just recapped, gave me a gotcha, in that I ordered the right value and voltage, but the part turned out to be a bipolar 'lytic'. Dang!

I sure recognize this predicament. The other day I pulled out 220 uF at 6.3 Volts. When I examined it turned out to be a bi-polar. I might have left it in there if I'd seen it was BP.:sigh: Are these like trying to find dragon's teeth or is it just where I am looking? The closest I can come from my sources is in 16 volts! I've been wondering which matress-pea would be bigger — the old one back in, or a new one at 16 Volts.:scratch2:

 

[seadzz]

Having a higher voltage is not a problem at all. If the old one is 220uf @ 6.3 volts and the new one is 220uf @ 16 volts it will work without any issues.

Bipolar caps are fairly common, you should not have too much trouble locating one.

Panasonic has a line and here is a link: http://dkc3.digikey.com/PDF/T061/1019.pdf

 

[lorne]

seaddz wrote:

Having a higher voltage is not a problem at all.

Thanks for your response. Your idea is what I have WANTED to believe. But, I continued to remember something I found on the net one day about voltage and electrolytic caps. I did not always take the advice, but recently I was moved to go over it again and put out some questions on AK. You can find the discussion here on a thread started by Rich P. — an excellent illustrated log of a recapping he did.

http://audiokarma.org/forums/showthread.php?t=63737

Here is what he wrote about voltage ratings and caps, and it confirmed what I had read years before:

As to using higher voltage ratings...The absolute upper limit is the minimum voltage necessary to keep the electrolyte formed. If you use too high of a voltage, your electrolyte will not properly form up, not will it stay formed, with various negative consequences (noise, leakage, etc.). With modern caps, you may get away with more, but I won't go higher than about 20% in voltage. The reason is, you don't know what voltage rating is actually needed, verses the voltage rating that the designer had to compromise with, originally. You have to do a significant amount of additional reverse-engineering to determine the safe voltage boundary (circuit design, and cap design). Additional considerations, are the higher losses at lower voltages, for larger cap volumes, etc.

Over the short haul there should not be very significant issues if one overlooks Rich's last sentence. But if longevity is an objective, it looks like using the original voltage is a good idea.

I am trying to order from inside Japan where I am living, but thanks for the Digikey suggestion. I'll take a look for low-voltage BP's.

 

[LBPete]

I am trying to order from inside Japan where I am living, but thanks for the Digikey suggestion. I'll take a look for low-voltage BP's.

Lorn, if it's a hassle to order from Japan, and you have a little time, let me know what you want and I'll add them to my next Digikey order and forward them to you.

- Pete

 

[lorne]

Thanks Pete — and the same goes here if there is something that is a hassle for you here in Japan. Singapore and Malaysia are easier places to order from, so I'll try there before I tap you on the shoulder — thanks again. — Lorne

 

[lorne]

Pete: This 6.3 Volt scarcity has got me in travel mode: I'll be either on the night-bus or Shinkansen [Bullet Train] that goes to Tokyo — Akihabara to be exact. The nickname for this 'electronics city' is Akiba. The area is changing a lot — some of it in ways unrelated to electronics and electrical products. Apparently a lot of the old specialty shops have already gone, such as one that was well-known for supplying almost any IC anybody would want. But, it would seem that, from what I have found on the net, there is still a concentration of small suppliers. Any curiosity can be satiated in English here: http://www.interq.or.jp/japan/se-inoue/e_map.htm By navigating around, you can find descriptions and locations of these legendary, tiny shops. I aim to find a few shops that will be willing to mail to me up here in Tohoku. And I am convinced that I will find the elusive 6.3 Volt 220 uF B.P. BUT, to be sure there is not a lot of WAF in the project :zoom:

 

[LBPete]

Lorne, Thanks for the link. As the value of property in Tokyo increases, more of the small shops will be squeezed out. As I may have mentioned, I had a couple of opportunities to wander around in the Akihabara district in the mid an late 1980s. I stumbled into back street that was lined with arcade like booths, each with a component specialty. Kind of like the links in the website you referenced but all right next to each other. It was facinating to see the variety of parts for sale.

Of course thats not the main stay of the Akihabara district. There is much more money to be made selling appliances and consumer electronics.

Digikey stocks a 6.3v 220uf Panasonic ECG cap for a wopping 38 cents. Air letter post to Japan is about $2.50. That's got to be cheaper than a ticket for the bullet train. Say the word and I'll add it to my next digikey order. (Although sending Panasonic caps to Japan is a little like shipping coal to Newcastle.)

- Pete

 

[lorne]

Pete: I sent you a private E-mail — Lorne