[sdiy] Update! Re: 78xx regulator gives negative output half the time

[Tom Wiltshire]

Seriously? What the hell happened to their QA?
Surely that kind of thing isn't good for business?

T.

On 29 Oct 2010, at 14:58, Dave Kendall wrote:

> This rings a bell.
> 
> There was a bad batch of LM7812s a while back - I forget where this was discussed - either here, or on electromusic.com, or possibly on the 9090 forum. I seem to remember they were outputting +21V.... not exactly what you want.....I can't remember whether national semi or fairchild parts were the culprits.
> 
> 
> cheers,
> Dave
> 
> On Oct 29, 2010, at 14:39, Karl Ekdahl wrote:
> 
>> Hi List
>> 
>> I have once again gotten this weird problem; unit does not start once plugged in but if you immediately unplug it and plug it back in it starts up. The cuplrit is again a 7809 regulator.
>> 
>> Now this time the back-to-back diode network did *not* work to my big horror. I do however think i've found the problem; seems like the Fairchild LM7809ACT does not work, though the LM7809CT does! The only difference i can find inbetween the two is that the latter has a wider temperature range and slightly less awesome line/load regulation.
>> 
>> So before i order 50 of the LM7809CT as replacements i've got three questions:
>> 
>> 1. Does this seem right? Can anyone refute my findings?
>> 
>> 2. Do you think this is a manufacturing error on the part / a bad bath or just different behavior?
>> 
>> 3. If this is not a bad batch of parts, how the hell can one make sure that you don't get the sensitive / weird parts if (like now) the part that first worked isn't in stock? There are literally 100's of 78xx/79xx regulators and i guess some work and some don't. The first time i had this problem (Re: this e-mail) i was working with some 7812 regulators - perhaps there's a 7812 regulator that will work?
>> 
>> Oh btw. i'll get back to y'all on this once i know all the hard facts, maybe it's time to watch out for any ACT regulators...
>> 
>> Thanks!
>> 
>> Karl
>> 
>> --- Den tors 2010-04-29 skrev Ian Fritz <ijfritz at comcast.net>:
>> 
>>> Från: Ian Fritz <ijfritz at comcast.net>
>>> Ämne: Re: [sdiy] 78xx regulator gives negative output half the time
>>> Till: "Karl Ekdahl" <elektrodwarf at yahoo.se>, synth-diy at dropmix.xs4all.nl
>>> Datum: torsdag 29 april 2010 02:13
>>> At 05:42 PM 4/28/2010, Karl Ekdahl
>>> wrote:
>>>> However i'm still not entirely sure i understand why
>>> this is happening in the first place, JH suggested he's seen
>>> it while doing circuits with unevens loads - but i've built
>>> literally 100s of circuits using this very same PSU scheme -
>>> that definitely have uneven loads - and i've never had this
>>> happen before.
>>> 
>>> Different manufacturers?  There's been trouble with
>>> this reported in the past.
>>> 
>>> Ian
>>> 
>> 
>> 
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