Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1] 2 Next   Go Down
  Print  
Author Topic: Destroyed My Daiwa PS-220 Power Supply  (Read 6985 times)
N4HMR
Member

Posts: 6




Ignore
« on: February 04, 2013, 07:43:58 PM »

I did something I really shouldn't have, and now I wish I hadn't.

My Powerfast 7000 watt portable generator wasn't doing a good job of putting out voltage (measured a whopping 6.8 vac on the 120v outlets at normal engine rpm's).  After finding the original 70mfd capacitor to be terribly disfigured (plastic type housing) that measured a steady 0 (as in zero) mfd, I came to the conclusion that it might be bad!  Reckon?  So, I got a new one that measures about 71.3 mfd (5% tolerance).

I had read in the manual for the unit that symptoms of no or low voltage output could be either a bad cap or that the stator winding had lost it's residual magnetism.  If the cap was found to be ok, then to "Apply 12-volt battery to capacitor terminals
for 2-3 seconds" to restore the magnetism.

I was using my Daiwa PS-220 to put a small charge on the cap (while on the bench)  before installing it - which I found to bleed down to almost nothing rather quickly, and was using the *6 amp* terminals side of the PS-220 to do so. 

When I connected the cap and started the generator, I still had low voltage.  So, I shut it down and proceeded to jumper the PS-220 to the cap terminals with the winding connectors attached to the posts as well.  I saw a sizable spark when I touched the second lead to the cap post but followed the instructions and held it on for about two seconds.  Cranked the generator but still had the same low voltage.

I then looked at the PS-220 and saw the volt meter needle pegged hard to the right at 20 volts!  UH, OH!  Not good!
The voltage adjustment pot had no effect on the reading.  I then struck the two leads together, and the meter needle immediately went to zero, and is still there. 

Well, Crap!  Blew up my Dang power supply and the @#$% generator still ain't working!  Not happy!  I then wheeled the generator over to the car, and pulled juice off the car battery.  It took two shots to the cap but the 2nd one brought it back to life.  So, I at least got something out of the deal.  Mumble.

Now, as for this deceased power supply, I popped the cover off and the only IC items I saw were one transistor and a NEC C324C, which is a 14-pin Low Power Quad  Operational Amplifier.  Can't see what the transistor is without dismounting the board they are on.

1. Does anybody out there have a schematic for this beast?  Going to the Daiwa website is a useless joke!  I mean, are they still even in business???  I do see Daiwa SS-330W's and SS-505's advertised but they may be leftovers.  Dunno.

2. Has anyone repaired one of these units, or have any suggestions?

I am off the air now so need any help I can get.  Many thanks for all ideas.
Logged
K8AXW
Member

Posts: 3723




Ignore
« Reply #1 on: February 04, 2013, 09:53:51 PM »

I wasn't able to find a schematic for the Daiwa PS-200 but did find one for the PS-300.  From what I see it's almost identical to the Astron power supplies. 

I doubt seriously if you "destroyed" the power supply but but understand you will no doubt be replacing a few components.

It appears that the Daiwa uses Japanese numbered output transistors.  They are 2SD... but the numbers on the schematic I downloaded aren't very clear.  Nevertheless, the 2N3771 transistors can possibly replace them.

I would download the readily available schematic for an Astron power supply that closely resembles the PS-220 power wise.  Look the schematic over and compare it to your supply. 

If I was a gambling man I'd say offhand you smoked the output transistors and possibly the regulator chip on the PCB. 

Pull the pass transistors one at a time and check them with a VOM. 

Cross reference the 14pin chip and see if it is an equivalent to the LM724 regulator chip.  (the PS-300 uses the LM724 regulator chip)

If the pass transistors are OK, come on back and we'll go from there.

I'm confident the supply is salvageable.



Logged
KA4POL
Member

Posts: 1962




Ignore
« Reply #2 on: February 04, 2013, 10:17:29 PM »

The Daiwa PS has a different way for regulation. They are using the LM324 which contains 4 OpAmps whereas the Astrons use the good old LM723.
Logged
AA4HA
Member

Posts: 1386




Ignore
« Reply #3 on: February 05, 2013, 04:33:27 AM »

Hmm, transformer, bridge rectifier, filter caps... you can pretty much choose your own form of voltage regulation.

I try to not get too attached to replicating any specific manufacturers way of voltage regulation if they use weird circuits or unobtanium parts.

You could give the supply a variable output or current limiting protection with a few extra components.
Logged

Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
WB6DGN
Member

Posts: 606




Ignore
« Reply #4 on: February 06, 2013, 01:34:21 PM »

If you have the second "winding" on the transformer, you could just replace the Daiwa regulator with a new Astron one.  They're cheap (last one I bought for an RS-35 was $20.00 + Ship) and reliaable and, best of all, readily accessible.
The high output voltage and lack of ability to adjust it screams "bad pass transistors".  That MAY be all that's wrong.  Whatever you do (except tossing it) you'll need to replace those, so that would be the first step.  Then you can decide where to go from there.
Tom
Logged
KE3WD
Member

Posts: 5694




Ignore
« Reply #5 on: February 06, 2013, 01:53:18 PM »

There's certainly nothing so wrong with the good old LM-324 comparator IC when used to drive a Series Pass transistor regulator.  Give or take circuit design. 

Check the Pass transistor, if gone, replace. 

Socket the LM-324 if it isn't already, pop another in there and check operation. 

Changing it to the Astron situation likely would not make it any more robust and from the number of Astrons that blow up every year, I'd be thinking it to be a step backwards?  Perhaps. 


73
Logged
KA4POL
Member

Posts: 1962




Ignore
« Reply #6 on: February 06, 2013, 09:55:39 PM »

I think it's not necessary to discuss design here. The fault did not come from a bad design.
Cut the connection to the pass transistors and check out how the regulator circuit works without them. This should narrow down the problem area.
Logged
KE3WD
Member

Posts: 5694




Ignore
« Reply #7 on: February 07, 2013, 07:26:24 AM »

I think it's not necessary to discuss design here. The fault did not come from a bad design.
Cut the connection to the pass transistors and check out how the regulator circuit works without them. This should narrow down the problem area.

Exactly.  The urge to "mod" rather than a simple and good Repair can often lead to other troubles. 

Consider that the Daiwa design in question obviously must have worked well for a considerable amount of time before this failure. 

73
Logged
K8AXW
Member

Posts: 3723




Ignore
« Reply #8 on: February 07, 2013, 09:23:35 AM »

A very long time ago I tried that "mod before repair" thingy.....ONCE!  I found out very fast that was a stupid move.  If it worked at one time, fix it. 

Leave the mods to a time when you can't stand seeing a working piece of gear ....work.
Logged
N4HMR
Member

Posts: 6




Ignore
« Reply #9 on: February 07, 2013, 07:13:57 PM »

Hello All -

First I want to thank all who have taken the time to make any suggestions.  Collectively it gives one a good bit to think about.

I have had all Heck break loose over the last three days, and am still grappling with some of those dubious pleasures.  How'se that song go - ''If it weren't for bad luck I'd have no luck at all!"! 

Anyhow, I hope (maybe) to have some time this weekend to look into, on, about, through and under this passel of electrical components to see if I can make any sense of it.  I'll reply when that happens.

Fred
Logged
K8AXW
Member

Posts: 3723




Ignore
« Reply #10 on: February 08, 2013, 08:09:56 AM »

Fred: 
Quote
under this passel of electrical components to see if I can make any sense of it.

At the risk of insulting your intelligence and or troubleshooting ability, may I suggest you concentrate on the pass transistors and the regulator chip, in that order?

There isn't any reason to pay attention to the "passel of electrical components."  Quite often it's difficult to see a tree when you're looking at a forest.

The pass transistors can be checked with a VOM and the chip can be replaced.  If it's soldered in the board, remove it and add a socket then the new chip.  Could save a lot of work in the future.

Come back and let us know what you found.

AL - K8AXW
Logged
N4HMR
Member

Posts: 6




Ignore
« Reply #11 on: February 18, 2013, 07:13:48 PM »

Hey All -

All I have time for here is a brief update.  Seems I can't get one problem dealt with without two more taking it's place.

Haven't had time to touch the PS other than to shove it to the back of the bench with all the Crap goin' on.  BUT, I did email Daiwa, and - LO and Behold - the Gent there sent me a copy of the schematic!  He said it was a REAL old supply, so I reckon they didn't have too many worries about releasing it.  Hey, works for me.

I honestly don't know when I'll get a chance to work on this thing but it doesn't look like it will be anytime soon.  But I know where all these suggestions are, and I will certainly review all when I do get the time.

Meanwhile, thanks again for the help, and I absolutely will update when I can do something on it!  Don't give up on me! 
Logged
K8AXW
Member

Posts: 3723




Ignore
« Reply #12 on: February 18, 2013, 09:48:15 PM »

HMR:  Any chance of you scanning that schematic and posting it on Photobucket or someplace similar?
Logged
KA4POL
Member

Posts: 1962




Ignore
« Reply #13 on: February 18, 2013, 10:23:15 PM »

Al's proposal is very important for us to support you.
Logged
N4HMR
Member

Posts: 6




Ignore
« Reply #14 on: February 21, 2013, 09:46:02 AM »

Hey -

I have the schematic saved as a 'jpg' file, but cannot see how I can attach it here.  I looked in the 'Help' section for posting attachments and it shows an icon for 'Insert Image' there (and it is flagged 'New'), but that icon does NOT appear on the Post Reply screen.  Huh??   Can that be done?

Also, I tried the 'Insert Email' icon, and that does NOT produce the url string as the Help screen indicates.
For ex: someone@somesite

NOTE: When I previewed this post, it throws away the leading and trailing 'email' structure showing in the Help example.

How the Heck is that string gonna grab the *RIGHT* email???  I have SCORES (hundreds?) of emails with that address!!
Makes no sense to me.

Huh?

Fred
Logged
Pages: [1] 2 Next   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!