Michael A. Terrell wrote:

If you read the datasheet, LM340 is the National Semiconductor name
for the 78** family. It is followed by a dash & the output voltage.

Yeah, for some reason I had the LM317 stuck in my head which was some kind
of variable regulator. It wasn't very good of a device, but was common.

It's still cheaper to buy the common values 10 or more at a time and
use the right part. You waste time & parts to kluge the wrong part into
the circuit, and both cost you money. In some types of repairs, you are
not allowed to kluge in the wrong part without a huge pipe of paperwork,
and I did a lot of that kind of work, from '72 until I was sidelined by
my health a few years ago.

The above comment depends on the situation. Of course it's better to use the
exact part and do the repair properly, but that doesn't hold true of all
circumstances.

Back in the 80's I was involved with a wholesale guy here in Illinois out
near Rockford, he used to buy semi-trailers of returned merchandise and
closeouts, anything from clock radios, multi-band radios, cable converters
and some stuff I couldn't figure out its use.

At best, and I do mean at best, it was $2 a repair. Most of the time it was
50 cents, but parts were billed separate. On first thought, most people
would just laugh getting paid that little, but when you are looking at 3000,
4000 or 5000 peices with one group exceeding 20,000 items, it makes you
think.

Basically if you spent more than 5 minutes to repair it, you were doing
charity work. So it comes down to meatball surgury, cut out the bad part,
get a new fix in, button it up and move on to the next.

The majority of that crap had power supply problems, I'm talking the old,
linear device type, some kind of transformer, a couple diodes (if you were
lucky) and maybe 1 filter cap. After that it was transistor de'jour to feed
the device. Some of these had PNP where it was supposed to be NPN (I guess
2SB is close enough to 2SD), or on some, they were missing altogether.

Identifying a zener diode, ha, didn't have the luxury. Most of those were
probably some pin diode from the 60's that looked close enough.

Point was, I made a lot of money doing the kludge, paying someone to tack
solder a couple parts to a 7805, pay someone else to clip here, clip there
then solder in the kludge to these points, instant 9v regulation. Plug it
in, if it works, on to the next.

Was easier using the mess soldered onto the 78xx than getting the right one
because you had leads to work with, not jumpers, which attaching them would
of slowed things down.

It wasn't rocket science, wasn't elegant and in some respects, was kind of
embarassing. But it was work, paid well if you could figure out the routine
and overall made everyone happy.

The only major botch job I did where nearly everything came back to be
reworked was these goofy modulators, which I can't even imagine to this day
what they were being used for. They wanted to retune them from a channel 2
output to channel 4, which after playing with a couple, seemed to be a
simply coil retuning, but turned out they weren't 75 ohm "things" but 50
ohm, so they didn't work wherever they ended up.

I hated that, not only because of doing it twice, but the chamber that the
coils were in was sealed via a half dozen sheet metal screws that were like
1/8", tiny ****ers. I had to have custom made hardened steel bits made
because any socket or hand tool would simply wear out after a days use. And
of course, the heads to them mostly didn't like being untighten and tighten
twice.

Anyway, getting back to the subject, I understand what you are saying but I
wasn't employed by NASA here. That guy was trying to make a dollar on
something that probably cost him 25 cents. Here in Chicago there was a lot
of opportunities like him. We used to have these places that sold "hotel
tv's", cheap 19" RCA sets (usually) for half or less what they were going
for retail. In the early 80's, most video stores that did tape rentals also
did machine rentals, they were still too expensive for everyone to own one.

All of the above didn't care about the quality of repair, just the costs.
Even if up front you told them that on the cheap it may only last 3 months,
if it was a lot less than doing it the right way, cheap it was.

Just saying that LM78xx series is a versatile little device that can be used
in a far wider arena than what the spec sheets say.

-bruce