Replacing rail capacitors

thedeal7235 · Post by **thedeal7235** » Sat Jan 03, 2009 8:34 am

Can anybody tell me that when u go to install the new rail caps if they should be shorted before installing on board?- I have the power and ground input shorted together since Im working on the amp, so I dont know if that prevents any issues when going to install new ones or not, or as i mentioned, I need to also short the 2 new ones prior to adding, I did short the old ones with an insulated screw driver prior to working on them-thanks, and bare with me, im still learning

nico boom · Post by **nico boom** » Sat Jan 03, 2009 9:44 am

Just check if there is any current in them with your DMM; most of the time new caps are completely without any load.
If not sure; just short the connectors for 20-30 seconds prior to installing with a small 12 volt lightbulb.
I always measure them for load with a DMM, and exact capacitance with a capacitance meter before installing them.

Good luck.

Post by **Jacampb2** » Sat Jan 03, 2009 1:03 pm

nico boom wrote:and exact capacitance with a capacitance meter before installing them

Interesting that you brought that up. Just the other day I saw a online news (like hack-a-day type news, not sure if it is legit) article about far east counterfeit capacitors showing up. The caps had much smaller caps actually in a large can. There was chatter about it being someones attempt at a joke, and that it wouldn't be cost effective, but with china stuff not from known sellers, well I could see about anything.

Best case scenario if it is happening, the caps don't do a good job filtering because they are way under size. Worst case scenario is that the cap is way underrated for voltage, and still the same capacitance as the original, and explodes when the WV is exceeded... Most of us who tinker know that there was a plague that swept through the semiconductor market a few years ago with counterfeit BJTs and Mosfets. They just burn up, but at least they were not as potentially dangerous.

Oh, and another one. I saw a post on another board I frequent about counterfeit service panel breakers. One of the guys on the forum opened up a ebay hong kong purchase, and found nothing but a straight piece wire in the housing along with the mechanics to make the switch "feel" right...

Long story short, be sure you trust your source, and always attempt to test replacement parts to the best of your ability before installing.

Jim Truett · Post by **Jim Truett** » Sat Jan 03, 2009 3:50 pm

There was a huge problem with counterfit Toshiba TO3PL transistors back in the day. These are the same units PG has used in their output stage in the MS, ZPA, and ZX amps. They were basically good for half of Toshiba's rated power.

GX3 · Post by **GX3** » Sat Jan 03, 2009 6:28 pm

how much might a capacitance meter cost. I have used them but never had to buy one???????

thedeal7235 · Post by **thedeal7235** » Sat Jan 03, 2009 7:47 pm

Well, Im not sure what happened when i went to desolder the old rail caps off, but it fried out one of my solder irons???? anyways, the new ones went in no problem, and im gonna fire it up tomorrow-so thanx to all who gave opinions and suggestions-(didnt short/discharge new rail caps, no issues when installing) -Maybe somehow my old sodler iron just shorted????? no clue what happened, well see if theres issues tomorrow when i hook it up-C

Post by **Jacampb2** » Sun Jan 04, 2009 9:01 am

thedeal7235 wrote:Maybe somehow my old sodler iron just shorted?????

Probably the most likely explanation. The heating elements are insulated from the tip, so even if you accidentally shorted a cap with the iron, it should not have taken out the element. More expensive ESD safe irons will have the tip at ground potential to the ground in your home outlet, or a ground post on the back of the controller. Most inexpensive irons are not even grounded, to it is very unlikely that the caps blew up the iron.

BTW, it is high time you start saving for a good soldering station if you are going to keep up this type of work. It will make your life sooooo much easier.

Later,
Jason

thedeal7235 · Post by **thedeal7235** » Sun Jan 04, 2009 9:07 am

I hear you

-what would u rec.???

Post by **Jacampb2** » Sun Jan 04, 2009 9:19 am

I love my Hakkos. I bought them both on eBay a few months back. I have a thread in this section somewhere, title something like "got a new toy". I purchased both for less than $50. The Hakko 936 is absolutely the best station I have ever used. It heats up to 650° in less than one minute and has extremely precise tip control. The only downfall is that the iron tips contain both the element and thermocouple all in one assembly, and are quite expensive. I have no spent more on different tips for the iron than I did on the station itself.

The other station I got was a Hakko 927. It is somewhat rare, and was only made for a little while. The 927 looks very similar to the 936 but takes a different iron. The 927 iron is slower to heat up, and tip temp fluctuates more, mostly due to the iron design. If memory serves, it is something to do with the way the tips are designed. The 927 iron takes a much less expensive tip because it does not have the thermocouple or element (maybe both, I can't remember) built in, but this also makes it a bit more sluggish. I rarely use the 927.

If you cruise the bay for these models, look for ones being sold w/o their lock out card. They are much, much cheaper, because everyone things that w/o the card you cannot change the temp. To a point this is true, but I can point you toward instructions on how to modify it to change temps w/o a card.

Weller makes some decent stations, but they go fairly high due to the name. Hakko is a leading industrial brand, and probably more likely to be found in a professional environment than a well station...

thedeal7235 · Post by **thedeal7235** » Sun Jan 04, 2009 9:30 am

Thanks Ill check it out