Follow ups to Cap buy request

Sun Jan 27 15:58:05 CST 2013

If you've not seen it, this page might be of help to you:  Index of Astron Power Supply Information and Schematic Library

louie
wa3ymh

On Jan 27, 2013, at 2:41 PM, Michael Chisena <ka2zev at yahoo.com> wrote:

> Hi all,
> This is a follow up note as to what is going on.
> Current status of the Astron 50amp PSU project.
> Last Saturday I briefed the client in on the parts cost status and he decided to 'scrap' the unit with me.
> So now if I fix it, I get to keep it.
> 
> Some of the members were kind enough to take a moment to answer.
> Here is what Mr Spargur sent me.
> 
> ............
> 
> It is a situation where you don't know the stress the other cap was placed
> under and its condition.  It is a good idea when one fails to replace both
> at the same time.
>     V/R
>     Richard K. Spargur
> 
>     K3UI
> ..............
> My answer was sent off list but here it is.
> For the right people an email is about as private as a post card.
> .........
> RS,
> Yes that is the right way to do things.
> 
> When ever possible I do try to do that.
> 
> The problem is 'consumer repairs'. 
> We think one way, clients think another.
> 
> I tell the client that the thing just 'ate' $200 in parts.(worst case based on Mouser prices)
> The unit might cost 250 dollars to replace.
> My chance of making a buck on the deal,  heads into the relm of zero probability.
> 
> So if an AMRAD member sell me one or two fresh caps for less than the supply house price, it's a plus.
> That I might be able to sell the client. 
> Add to that fixing the 'acid spill' issue would make this a worthy repair.
> 
> If the client refuses the estimate, good chance I will get the thing ' for free' or in exchange for a bench charge.
> 
> That would make it worth fixing for personal use.
> For the moment I have a small 30 amp switcher that I use for bench stuff.
> This would give me a bit more latitude to fix higher power gear.
> 
> Im trying to break into a new product line.
> 
> These huge car audio amps. The ones we hear from two blocks away.
> Yeah they are nasty and obnoxious but there is money in it if one can fix them.
> This thing makes 2K watts of bass and feeding it takes real power.
> 
> http://www.flickr.com/photos/90108848@N00/sets/72157631787506891/
> 
> As you can see the caps in it exploded, apparently from voltage starvation of the switcher.
> 
> If I can get good at those, it's a new product to my line.
> 
> Tried to break into the CNC machine repair biz, got exactly one board in.
> http://www.flickr.com/photos/90108848@N00/sets/72157629148546241/
> Very specialized business.
> 
> APRS conversions would be a good line if the economy had not gone sour.
> http://www.flickr.com/photos/90108848@N00/sets/72157623358841596/
> 
> So the plan is to fix what I can for who I can, and pocket the bucks.
> 
> Hope all is well on your end.
> Mike
> ...................
> So that was my answer. 
> 
> Yet what Mr S said was accurate and true.
> 
> Did some digging. Found on Ebay of all places someone selling the right part for about $18 per cap.
> Thinking real hard about pulling the trigger on two for that price.
> 
> Chip sent the below.
> 
> My answers will be (interlaced) as to cut down on the size of this e mail.
> ...................
>  Using a 50 Ampere power supply as a charger for a lead acid battery is a LARGE move away from goodness.  Two Amperes at 13.6-13.8 Volt is all you want.  I'll bet it didn't take all that long for the battery to boil over, especially if the PS was set to more than 12.6 Volts.
> 
> (I have found that clients don't like to admit mistakes. 
> I would gain nothing by trying to extract an answer that would be embarrassing.
> If getting paid is a goal, then we don't embarrass our clients. 
> We take the item, say 'Yes Sir!' and do our best.
> You right as well. 
> People who do not do this for a living make errors. 
> The deal I have with my dentist is this. 
> I won't fill teeth if he won't fix amplifiers. 
> It's been a good deal so far.
> Not everybody is as sharp as my dds.)
> 
> I'll wager they used the combination to power a display of car electronics.  
> Not a bad plan, but they didn't need the battery -- nearly nothing will draw more than 50 Amperes.  
> 
> (His sound board has about 20 radios in it plus a selection of big audio amps that can be matrixed in. 
> Crank one with some low Z speakers, and the current draw is up there.
> The standby current has to be this side of amazing. 
> Im guessing 15 amps of standby draw alone.
> 
> When turned on modern car radios have fancy displays and all the big amps have DC to DC systems running in them. 
> That's a lot of standby by current.
> Fixed this unit prior to the pending Astron. 
> He blew the guts out of this choice bit of crap.
> 
> http://www.flickr.com/photos/90108848@N00/sets/72157632568360299/
> 
> The text in the article explains how it all went down.
> Fortunately there was an OVP in the Pyramid PSU that did keep the sound board from blowing up.)
> 
> If something does, they need to rethink how things are wired up. 
> Two diodes (hopefully Shotkey) and a properly sized power resistor can keep the battery in fairly good health.
> 
> (They are nice enough guys but some things are not part of the skill level.
> 
> Just today I delivered a simple little LM317 voltage reducer so one client can run his Ipod music player.
> 
> http://www.flickr.com/photos/90108848@N00/sets/72157632624817252/
> 
> The guys were trying to run it on 12 and the label says 7.5 volts.
> If this little thing works, there may be a small production run involved.
> Apparently it's a common thing to want this feature in auto sound.
> Seems hams solved this years ago using hand held radios in cars.)
> 
> Before you replace the cap, put an Ohm meter on the diodes to check for shorted diodes.  
> ( Did that. I cheat. 
> I have what I call a 'cheap curve tracer' and tested them that way.
> The gizmo impresses a small AC across a semiconductor and if the junction is good, I get a "L" shaped display on the scope.
> Much quicker than poking with a DMM and with it I can see if the junction is damaged and examine for leakage
> Anyhow, they checked just fine.)
> 
> Often the cap will take out diodes if the cap shorts.
> 
> (This is a judgment call. I don't think it shorted, just blew its guts out.)
> 
> When you replace the cap, be sure to check ripple.  
> 
> (That is part of the standard service. 
> With the electronic load, I draw a good chunk of current.
> 
> http://www.flickr.com/photos/90108848@N00/8398820816/in/set-72157632565039329/
> 
> Check for voltage drop.
> 
> http://www.flickr.com/photos/90108848@N00/8397727999/in/set-72157632565039329/
> 
> Then I punch the HP3456A (over kill of a meter) into AC and take a ripple reading.
> It's rare I see more than half a mili volt on an Astron with a heavy load on it.)
> 
> The Ohm meter test of the diodes doesn't always show up bad diodes.  
> AC across a large electrolytic can quickly overheat it, causing what you already have.
> 
> (That goes back to what Mr S had to say.
> One is destroyed the other is not to be trusted.
> The problem is not one of technology but customer relations.
> Now that the PSU is mine I can do what I want with it.)
> 
> Good luck, and if you need an example of a working 50M, I have one here. 
> 
> (Thanks for the offer. 
> I have fixed a number of big Astrons in the last year.
> No need to risk injury lugging it up the stairs.
> The Repeater Builders Web Site has a great collection of schematics for these.)
> 
>  It really is a bear to move around.
> 
> (No kidding. I use a hand truck to get them from the apartment to the vehicle.
> Many thanks for the offer.)
> 
> ............
> 
> All
> That brings you up to date on the project.
> 
> Will see if I have to buy new caps, ebay caps, or not.
> 
> May even call the OEM and see what their price is, bet they have pallets of them in stock.
> 
> Be well there.
> Mike
> 
> Michael F. Chisena
> KA2ZEV at Yahoo.com
> 703 863 4574
> 
> "You are, what you do, when it counts" 
> The Masso
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