AF6AY wrote:
On Mar 21, 4:31�pm, Joerg
wrote:
AF6AY wrote:
"Joerg" posted on Fri, Mar 20 2009 6:06 pm
ken scharf wrote:
JIMMIE wrote:
Relays are ok in those applications, where there are actual currents
flowing. What I meant was pure signal switching with no DC currents.

That's called "dry" switching in the electronics industry, has been
called that for over a half century.

Sealed relays, Reeds, mercury-wetted and such work quite well there. But
non-sealed versions have issues and a snap-on plastic cap ain't a seal.

Didn't say that that it was a seal. But...there are many kinds of
'seals' and there are many kinds of contact alloys which few hobbyists
investigate.


Most must make do with whatever places such as Digikey offer at
affordable cost.


Those problems became really nasty after we moved across an ocean and
all this stuff was in a sea container for two months. After that almost
all the band switching relays had problems, had to clean all of them.
Now I am down to one sticky relay every couple month or so.

My wife and I own a nice 2005 model Chevrolet Malibu MAXX that we've
driven in both driving rain with some intermittent ice to Wisconsin
from California and back, to Washington state from California and
back. It has two little boxes of many small-signal relays, only a
very few qualifying for large-signal types. Never a problem since we
got it in late June of 2005. Those relay boxes all have lids and the
small relays have little covers and that auto has definitely been
exposed to the environment many times in the last 4 years.


Sure, but in a car relays always switch something that draws a serious
current, more than a few milliamps. That works for a long time. Well,
until a "weld wart" shows up, like it did on a relay in out Genie garage
door opener.


I can sympathize with your bad sea container shipping experience but
consumer-grade radios (such as for amateur radio) were never designed
to be exposed to sea evnvironments. Ask yourself how all those off-
shore made radios made it to the USA? Inside standardized container
boxes.


Usually they are carefully packaged and silica gel is included. When you
move that usually ain't the case. Plus the radio was quite old by that time.


I didn't make my comment lightly or pretend that I know everything
there is to electronics. I do know, by a rather large set of
experiences that 'dry' circuit relays (hermetically sealed OR by
reasonably-good individual covers) will work without having to be
'operated many times' in order to 'clean their contacts.'


Hmm, I've had that happen even in $xxxxx lab gear, not quite
consumer-grade. Never really with mil gear though but those guys can
often design to "the sky's the limit" cost goals.


I'll cite one application that is military, the US AN/PRC-104 manpack
HF transceiver. About one-third of that backpack radio is an
automatic antenna tuner so that one whip length can be optimized for
best electrical characteristics. It does that with a rather
conventional microprocessor control driving two banks of binary-
sequence inductance and capacitance values switched by relays. It has
been in operational status with the US Army since around 1984 and is
expected to be phased out soon in favor of more modern HF-to-UHF
transceiver designs. It's been a while since I've seen the guts of it
but I don't recall that it had any hermetically-sealed relays in it.


But I bet no expense was spared to pick the very best parts for that radio.


Right now I'm beginning to start cutting holes for a rebuild of an
'ancient' HF receiver once made for my late father wanting to tune to
some SW BC stations, principally Radio Sweden back in 1964. I've been
fortunate to get a large collection of North Electric small sealed
relays dating back to about 1955 production which I've already
breadboarded for bandswitching use. Very familiar with relay testing,
I found NO problems from 'dry' contact switching. The low capacitance
to ground and minimal series inductance from the contact set do NOT
upset any of the L-C circuits being switched.


Sealed relays are ok. I also have a few really old ones here and so far
they have never let me down. But I don't have enough to equip a filter
bank with 15-20 in- and outputs. For that I've got a stash of HSMP-3810
PIN diodes.


replaced with PIN diode circuits and that, of course, made the issues
completely go away. But it's always a hassle to do in an exisitng circuit.

Yes, I have that in the filter board of my two decade old Icom IC-R70,
all switched with 'RF switch' diodes (no registry number). If needs
be, that entire filter board could be enclosed to prevent any problems
from the environment. Icom used that sort of semi-conductor switching
for ease of overall parts cost along with reduced labor costs to
Icom. Such work fine at the LOW impedances involved (50 to 75 Ohms)
but I've tried to duplicate that at 10 KOhms on a breadboard and have
run into problems with diodes' own impedances affecting circuit
operation. Those could be solved, I'm sure, but I didn't care to
spend weeks fiddling with them for my rebuild project. The relay
contact set had only the shunt capacity and series inductance to
contend with and those were very low values and easily compensated for
alignment.


Yeah, anything above 1K or so is less suitable for diodes. That's where
JFETs come in which, in turn, are not so hot for anything low impedance.
Unless you use the fat expensive kind and they've got too high
capacitances. Many fine FETs like the P8000 have gone over the rainbow
bridge by now. I guess they only found homes in ham gear and that wasn't
a large enough market.

--
73, Joerg

On Mar 23, 3:32�pm, Joerg
wrote:
AF6AY wrote:
On Mar 21, 4:31 pm, Joerg
wrote:
AF6AY wrote:
"Joerg" posted on Fri, Mar 20 2009 6:06 pm
ken scharf wrote:
JIMMIE wrote:
Relays are ok in those applications, where there are actual currents
flowing. What I meant was pure signal switching with no DC currents.

That's called "dry" switching in the electronics industry, has been
called that for over a half century.

Sealed relays, Reeds, mercury-wetted and such work quite well there. But
non-sealed versions have issues and a snap-on plastic cap ain't a seal..

Didn't say that that it was a seal. �But...there are many kinds of
'seals' and there are many kinds of contact alloys which few hobbyists
investigate.

Most must make do with whatever places such as Digikey offer at
affordable cost.

I disagree considering that Digikey is one of the largest
distributors
in the world of electronics and offers so many different models AND
price ranges. Then there is Mouser, and Newark, and Allied, and
Jameco, and Ocean State, and Futurlec, and....a whole bunch of
them. None of those are 'giving away' anything.

Sure, but in a car relays always switch something that draws a serious
current, more than a few milliamps. That works for a long time. Well,
until a "weld wart" shows up, like it did on a relay in out Genie garage
door opener.

I will disagree again, but not on our particular Chevrolet...I only
got a
glance at the electronics wiring manual at a local dealership service
shop and NOT all the controlled circuits were "serious current" ones.
But, if you are convinced that they ALL are, I can't convince you...

Hmm, I've had that happen even in $xxxxx lab gear, not quite
consumer-grade. Never really with mil gear though but those guys can
often design to "the sky's the limit" cost goals.

Sorry, but that is URBAN MYTH among amateurs. What amateurs
don't realize is that components are elevated in cost by EXTREME
ENVIRONMENTS required. Sure, everything at room temperature
works dandy and one can use any kind of schlock parts and get away
with it. Freeze it below brass-monkey temps or heat it more than
boiling water, drop-kick it across the room, run it under extreme
vibration, it MUST WORK. Put most ham gear through that and you
won't have enough left to sell anything but its manuals on e-bay.
Been
there, done that for years...its what I did for a living.

----------------on the AN/PRC-104 HF transceiver
But I bet no expense was spared to pick the very best parts for that radio.

I'll bet you've never seen the inside of it, let alone talk with any
of the
staff at Hughes Ground Systems that designed it. If you want to
investigate it, the TMs (user to depot level) are available on the
'Web.
Hard to find and you may need special clearance to access some
military sites nowadays, but it is available for nothing. If you want
to
pay money for such a manual, fine, those are easier to get.

Sealed relays are ok.

Thank you for such permission. I was using salvaged components
from junkyard electronics a half-century old and know how to test
things that are salvaged. Note: I'm not just making conversation
here,
I'm trying to point out a few things which defy Urban Myth and what
the ARRL deems 'useful' for amateurs.

I also have a few really old ones here and so far
they have never let me down. But I don't have enough to equip a filter
bank with 15-20 in- and outputs. For that I've got a stash of HSMP-3810
PIN diodes.

I'm not swayed or impressed by a bunch of house numbers. Neither do
I need over a dozen different things switching in/out. For that
matter, I've
tried out 3-penny-apiece 1N4148 diodes (100-lot price), plain old
ordinary
old-fashioned silicon switching diodes and they could work just fine
for
4 different HF circuits...but NOT easily for B+ at 100 VDC...and they
need
more circuitry for controlling them than just relay coils needing only
a back-
EMF clamp diode.

But, what the hey, if you are convinced in only your way of doing
things,
fine, go do it. Excuse me, I'm going off-line and spend some quality
workshop time putting some hardware together. QRT.

73, Len AF6AY

AF6AY wrote:
On Mar 23, 3:32�pm, Joerg
wrote:
AF6AY wrote:
On Mar 21, 4:31 pm, Joerg
wrote:
AF6AY wrote:
"Joerg" posted on Fri, Mar 20 2009 6:06 pm
ken scharf wrote:
JIMMIE wrote:
Relays are ok in those applications, where there are actual currents
flowing. What I meant was pure signal switching with no DC currents.
That's called "dry" switching in the electronics industry, has been
called that for over a half century.
Sealed relays, Reeds, mercury-wetted and such work quite well there. But
non-sealed versions have issues and a snap-on plastic cap ain't a seal.
Didn't say that that it was a seal. �But...there are many kinds of
'seals' and there are many kinds of contact alloys which few hobbyists
investigate.
Most must make do with whatever places such as Digikey offer at
affordable cost.

I disagree considering that Digikey is one of the largest
distributors
in the world of electronics and offers so many different models AND
price ranges. Then there is Mouser, and Newark, and Allied, and
Jameco, and Ocean State, and Futurlec, and....a whole bunch of
them. None of those are 'giving away' anything.


Sorry, maybe I didn't express it well enough. My point was that not
everyone has a mil budget or a Rockefeller-sized bank account ;-)


Sure, but in a car relays always switch something that draws a serious
current, more than a few milliamps. That works for a long time. Well,
until a "weld wart" shows up, like it did on a relay in out Genie garage
door opener.

I will disagree again, but not on our particular Chevrolet...I only
got a
glance at the electronics wiring manual at a local dealership service
shop and NOT all the controlled circuits were "serious current" ones.
But, if you are convinced that they ALL are, I can't convince you...


Interesting, my car doesn't have that. Now I am curious. What are they
switching in a car where there is no DC current?


Hmm, I've had that happen even in $xxxxx lab gear, not quite
consumer-grade. Never really with mil gear though but those guys can
often design to "the sky's the limit" cost goals.

Sorry, but that is URBAN MYTH among amateurs. What amateurs
don't realize is that components are elevated in cost by EXTREME
ENVIRONMENTS required. Sure, everything at room temperature
works dandy and one can use any kind of schlock parts and get away
with it. Freeze it below brass-monkey temps or heat it more than
boiling water, drop-kick it across the room, run it under extreme
vibration, it MUST WORK. Put most ham gear through that and you
won't have enough left to sell anything but its manuals on e-bay.
Been
there, done that for years...its what I did for a living.


As I said this was high-Dollar lab gear. The kind where they don't even
flinch when an engineer says "this needs a piece of rigid coax".


----------------on the AN/PRC-104 HF transceiver
But I bet no expense was spared to pick the very best parts for that radio.

I'll bet you've never seen the inside of it, let alone talk with any
of the
staff at Hughes Ground Systems that designed it. If you want to
investigate it, the TMs (user to depot level) are available on the
'Web.


I've served (army), had to deal with radio/telco equipment. Cleaned many
relays there with Emery paper and alcohol. There is a reason for
instructions like this:

http://www.ansaldo-sts.com/EN/Ansald...y_Cleaning.pdf


Hard to find and you may need special clearance to access some
military sites nowadays, but it is available for nothing. If you want
to
pay money for such a manual, fine, those are easier to get.

Sealed relays are ok.

Thank you for such permission. I was using salvaged components
from junkyard electronics a half-century old and know how to test
things that are salvaged. Note: I'm not just making conversation
here,
I'm trying to point out a few things which defy Urban Myth and what
the ARRL deems 'useful' for amateurs.

I also have a few really old ones here and so far
they have never let me down. But I don't have enough to equip a filter
bank with 15-20 in- and outputs. For that I've got a stash of HSMP-3810
PIN diodes.

I'm not swayed or impressed by a bunch of house numbers. Neither do
I need over a dozen different things switching in/out. For that
matter, I've
tried out 3-penny-apiece 1N4148 diodes (100-lot price), plain old
ordinary
old-fashioned silicon switching diodes and they could work just fine
for
4 different HF circuits...but NOT easily for B+ at 100 VDC...and they
need
more circuitry for controlling them than just relay coils needing only
a back-
EMF clamp diode.


Yep, usually a resistor plus on occasion a choke in series with it, and
enough voltage to be able to be able to reverse the diodes far enough.


But, what the hey, if you are convinced in only your way of doing
things,
fine, go do it. Excuse me, I'm going off-line and spend some quality
workshop time putting some hardware together. QRT.


Have fun :-)

I am going to have to repair a bench supply that blew its power
transistors way down in there. Not much fun.

--
73, Joerg

Joerg wrote:
JIMMIE wrote:
On Mar 21, 5:11 pm, Joerg
wrote:
JIMMIE wrote:
On Mar 20, 6:47 pm, ken scharf wrote:
JIMMIE wrote:
On Mar 18, 9:24 pm, Robert casey wrote:
The design used plug-in coils for the osc and rf stages, and
they were double conversion designs, with a first IF of
1600 kc and a second IF of either 100 kc or 85 kc (when
using surplus ARC-5 IFTs.) The 1800 mc xtal you bought
your dad was used for the second coversion osc. to convert
the 1600 kc IF down to 100 kc. Many hams deviated from
the exact original IF frequencies (i.e. strong local BC
station on 1600 kc) which might explain why the xtal
was chosen for 1800 kc instead of 1500 or 1700.
We have a local mid power station at 1600KHz, WWRL, at my
parents' house,
so my father might have wanted to avoid problems with it.
His radio had a bandswitch instead of plug in coils, and he'd
receive
various broadcast SW stations. He wasn't a ham at the time just
yet.
I had a friend who was a retired engineer with GE turned TV tech who
built
one with a band switch and he later modified it to
be more of a general purpose SW receiver. His name was Olin Griggs.
Jimmie.
I once saw an article in 73 magazine showing a HB receiver that used a
re-worked turret tv tuner as a band switch. The coils were re-wound
onto the original forms, but some have just replaced the forms with
some
of the smaller sized toroid cores. I have a bunch of old tv tuners in
the junk box, but over the years the contacts have gone bad and now
show
a high resistance. Maybe they could be cleaned up, but it no longer
seems worth the effort. My new idea is to use miniature relays to
switch the circuits. I recently found nearly a gross of small relays
for free so why not?- Hide quoted text -
- Show quoted text -
I tried the TV tuner trick one time and it didnt work well at all.
Most tuners are tossed because the contacts fail. ...
Not really. Back then TVs were often tossed because the flyback xfmr had
blown and repair was deemed uneconomical. Or someone said that because
in reality they wanted that brand spanking new set that was one sale.

But this is so long ago that if there's any left the contacts will have
corrodes away.

[...]

--
73, Joerg- Hide quoted text -

- Show quoted text -

You must be younger than me, Ive replaced a lot of TV tuners and
flybacks. It was in the early 80s that i first noticed
TVs becoming diposable and quit working on them. Luckily for me there
was still a lot of other electtronic repair work needed to be done.
Most of the local industry was becoming more electronic oriented in
their equipment and needed someone to maintain their equipment but did
not want to hire a full time tech. The sawmills, textile plants, food
processing plants kept me pretty busy aand i enjoyed the work much
more not having to deal with the usual customers.


Same here, in the early 80's I began to refuse fixing TVs and stuff. But
even before that, I remember the flyback transformers for some sets
being so outrageously expensive that a repair plain didn't make sense.
Especially if it had taken out the H-deflection tube and some other
stuff with it or the set itself had already been quite tired at the time
it hissed its good-bye. This was in Europe.

I once fixed my parents tv by replacing the yoke, and I more recently
fixed my wife's tv set by replacing the flyback (AND the horizontal
output transistor). The first set was a tube type Zenith B&W 19"
portable. The second was a Trinitron color portable.
I think you still can get replacement yokes, flybacks, and even CRT's
for recent tv's. Good luck getting anything else!

ken scharf wrote:
Joerg wrote:
JIMMIE wrote:
On Mar 21, 5:11 pm, Joerg
wrote:
JIMMIE wrote:
On Mar 20, 6:47 pm, ken scharf wrote:
JIMMIE wrote:
On Mar 18, 9:24 pm, Robert casey wrote:
The design used plug-in coils for the osc and rf stages, and
they were double conversion designs, with a first IF of
1600 kc and a second IF of either 100 kc or 85 kc (when
using surplus ARC-5 IFTs.) The 1800 mc xtal you bought
your dad was used for the second coversion osc. to convert
the 1600 kc IF down to 100 kc. Many hams deviated from
the exact original IF frequencies (i.e. strong local BC
station on 1600 kc) which might explain why the xtal
was chosen for 1800 kc instead of 1500 or 1700.
We have a local mid power station at 1600KHz, WWRL, at my
parents' house,
so my father might have wanted to avoid problems with it.
His radio had a bandswitch instead of plug in coils, and he'd
receive
various broadcast SW stations. He wasn't a ham at the time just
yet.
I had a friend who was a retired engineer with GE turned TV tech who
built
one with a band switch and he later modified it to
be more of a general purpose SW receiver. His name was Olin Griggs.
Jimmie.
I once saw an article in 73 magazine showing a HB receiver that
used a
re-worked turret tv tuner as a band switch. The coils were re-wound
onto the original forms, but some have just replaced the forms
with some
of the smaller sized toroid cores. I have a bunch of old tv
tuners in
the junk box, but over the years the contacts have gone bad and
now show
a high resistance. Maybe they could be cleaned up, but it no longer
seems worth the effort. My new idea is to use miniature relays to
switch the circuits. I recently found nearly a gross of small relays
for free so why not?- Hide quoted text -
- Show quoted text -
I tried the TV tuner trick one time and it didnt work well at all.
Most tuners are tossed because the contacts fail. ...
Not really. Back then TVs were often tossed because the flyback xfmr
had
blown and repair was deemed uneconomical. Or someone said that because
in reality they wanted that brand spanking new set that was one sale.

But this is so long ago that if there's any left the contacts will have
corrodes away.

[...]

--
73, Joerg- Hide quoted text -

- Show quoted text -

You must be younger than me, Ive replaced a lot of TV tuners and
flybacks. It was in the early 80s that i first noticed
TVs becoming diposable and quit working on them. Luckily for me there
was still a lot of other electtronic repair work needed to be done.
Most of the local industry was becoming more electronic oriented in
their equipment and needed someone to maintain their equipment but did
not want to hire a full time tech. The sawmills, textile plants, food
processing plants kept me pretty busy aand i enjoyed the work much
more not having to deal with the usual customers.


Same here, in the early 80's I began to refuse fixing TVs and stuff.
But even before that, I remember the flyback transformers for some
sets being so outrageously expensive that a repair plain didn't make
sense. Especially if it had taken out the H-deflection tube and some
other stuff with it or the set itself had already been quite tired at
the time it hissed its good-bye. This was in Europe.

I once fixed my parents tv by replacing the yoke, and I more recently
fixed my wife's tv set by replacing the flyback (AND the horizontal
output transistor). The first set was a tube type Zenith B&W 19"
portable. The second was a Trinitron color portable.
I think you still can get replacement yokes, flybacks, and even CRT's
for recent tv's. Good luck getting anything else!


I think the real challenge will come when one of those monstrous LCD TV
sets goes on the fritz and it's anything other than the backlight
inverter that died.

--
73, Joerg

Joerg wrote:
ken scharf wrote:
Joerg wrote:
JIMMIE wrote:
On Mar 21, 5:11 pm, Joerg
wrote:
JIMMIE wrote:
On Mar 20, 6:47 pm, ken scharf
wrote:
JIMMIE wrote:
On Mar 18, 9:24 pm, Robert casey wrote:
The design used plug-in coils for the osc and rf stages, and
they were double conversion designs, with a first IF of
1600 kc and a second IF of either 100 kc or 85 kc (when
using surplus ARC-5 IFTs.) The 1800 mc xtal you bought
your dad was used for the second coversion osc. to convert
the 1600 kc IF down to 100 kc. Many hams deviated from
the exact original IF frequencies (i.e. strong local BC
station on 1600 kc) which might explain why the xtal
was chosen for 1800 kc instead of 1500 or 1700.
We have a local mid power station at 1600KHz, WWRL, at my
parents' house,
so my father might have wanted to avoid problems with it.
His radio had a bandswitch instead of plug in coils, and he'd
receive
various broadcast SW stations. He wasn't a ham at the time
just yet.
I had a friend who was a retired engineer with GE turned TV tech
who
built
one with a band switch and he later modified it to
be more of a general purpose SW receiver. His name was Olin Griggs.
Jimmie.
I once saw an article in 73 magazine showing a HB receiver that
used a
re-worked turret tv tuner as a band switch. The coils were re-wound
onto the original forms, but some have just replaced the forms
with some
of the smaller sized toroid cores. I have a bunch of old tv
tuners in
the junk box, but over the years the contacts have gone bad and
now show
a high resistance. Maybe they could be cleaned up, but it no
longer
seems worth the effort. My new idea is to use miniature relays to
switch the circuits. I recently found nearly a gross of small
relays
for free so why not?- Hide quoted text -
- Show quoted text -
I tried the TV tuner trick one time and it didnt work well at all.
Most tuners are tossed because the contacts fail. ...
Not really. Back then TVs were often tossed because the flyback
xfmr had
blown and repair was deemed uneconomical. Or someone said that because
in reality they wanted that brand spanking new set that was one sale.

But this is so long ago that if there's any left the contacts will
have
corrodes away.

[...]

--
73, Joerg- Hide quoted text -

- Show quoted text -

You must be younger than me, Ive replaced a lot of TV tuners and
flybacks. It was in the early 80s that i first noticed
TVs becoming diposable and quit working on them. Luckily for me there
was still a lot of other electtronic repair work needed to be done.
Most of the local industry was becoming more electronic oriented in
their equipment and needed someone to maintain their equipment but did
not want to hire a full time tech. The sawmills, textile plants, food
processing plants kept me pretty busy aand i enjoyed the work much
more not having to deal with the usual customers.


Same here, in the early 80's I began to refuse fixing TVs and stuff.
But even before that, I remember the flyback transformers for some
sets being so outrageously expensive that a repair plain didn't make
sense. Especially if it had taken out the H-deflection tube and some
other stuff with it or the set itself had already been quite tired at
the time it hissed its good-bye. This was in Europe.

I once fixed my parents tv by replacing the yoke, and I more recently
fixed my wife's tv set by replacing the flyback (AND the horizontal
output transistor). The first set was a tube type Zenith B&W 19"
portable. The second was a Trinitron color portable.
I think you still can get replacement yokes, flybacks, and even CRT's
for recent tv's. Good luck getting anything else!


I think the real challenge will come when one of those monstrous LCD TV
sets goes on the fritz and it's anything other than the backlight
inverter that died.

The backlight itself is actually part of the LCD panel in most cases,
so when that dies, you need to replace the panel, which means the tv is
toast.

Most of the other parts are low power, except for the panel drivers,
which themselves may be part of the panel!

ken scharf wrote:
Joerg wrote:
ken scharf wrote:
Joerg wrote:
JIMMIE wrote:
On Mar 21, 5:11 pm, Joerg
wrote:
JIMMIE wrote:
On Mar 20, 6:47 pm, ken scharf
wrote:
JIMMIE wrote:
On Mar 18, 9:24 pm, Robert casey wrote:
The design used plug-in coils for the osc and rf stages, and
they were double conversion designs, with a first IF of
1600 kc and a second IF of either 100 kc or 85 kc (when
using surplus ARC-5 IFTs.) The 1800 mc xtal you bought
your dad was used for the second coversion osc. to convert
the 1600 kc IF down to 100 kc. Many hams deviated from
the exact original IF frequencies (i.e. strong local BC
station on 1600 kc) which might explain why the xtal
was chosen for 1800 kc instead of 1500 or 1700.
We have a local mid power station at 1600KHz, WWRL, at my
parents' house,
so my father might have wanted to avoid problems with it.
His radio had a bandswitch instead of plug in coils, and he'd
receive
various broadcast SW stations. He wasn't a ham at the time
just yet.
I had a friend who was a retired engineer with GE turned TV
tech who
built
one with a band switch and he later modified it to
be more of a general purpose SW receiver. His name was Olin
Griggs.
Jimmie.
I once saw an article in 73 magazine showing a HB receiver that
used a
re-worked turret tv tuner as a band switch. The coils were
re-wound
onto the original forms, but some have just replaced the forms
with some
of the smaller sized toroid cores. I have a bunch of old tv
tuners in
the junk box, but over the years the contacts have gone bad and
now show
a high resistance. Maybe they could be cleaned up, but it no
longer
seems worth the effort. My new idea is to use miniature relays to
switch the circuits. I recently found nearly a gross of small
relays
for free so why not?- Hide quoted text -
- Show quoted text -
I tried the TV tuner trick one time and it didnt work well at all.
Most tuners are tossed because the contacts fail. ...
Not really. Back then TVs were often tossed because the flyback
xfmr had
blown and repair was deemed uneconomical. Or someone said that
because
in reality they wanted that brand spanking new set that was one sale.

But this is so long ago that if there's any left the contacts will
have
corrodes away.

[...]

--
73, Joerg- Hide quoted text -

- Show quoted text -

You must be younger than me, Ive replaced a lot of TV tuners and
flybacks. It was in the early 80s that i first noticed
TVs becoming diposable and quit working on them. Luckily for me there
was still a lot of other electtronic repair work needed to be done.
Most of the local industry was becoming more electronic oriented in
their equipment and needed someone to maintain their equipment but did
not want to hire a full time tech. The sawmills, textile plants, food
processing plants kept me pretty busy aand i enjoyed the work much
more not having to deal with the usual customers.


Same here, in the early 80's I began to refuse fixing TVs and stuff.
But even before that, I remember the flyback transformers for some
sets being so outrageously expensive that a repair plain didn't make
sense. Especially if it had taken out the H-deflection tube and some
other stuff with it or the set itself had already been quite tired
at the time it hissed its good-bye. This was in Europe.

I once fixed my parents tv by replacing the yoke, and I more recently
fixed my wife's tv set by replacing the flyback (AND the horizontal
output transistor). The first set was a tube type Zenith B&W 19"
portable. The second was a Trinitron color portable.
I think you still can get replacement yokes, flybacks, and even CRT's
for recent tv's. Good luck getting anything else!


I think the real challenge will come when one of those monstrous LCD
TV sets goes on the fritz and it's anything other than the backlight
inverter that died.

The backlight itself is actually part of the LCD panel in most cases,
so when that dies, you need to replace the panel, which means the tv is
toast.


Often you can get to that inverter. Then if you are lucky it's the two
transistors. If not it's usually the transformer and then the catalog
chase begins.


Most of the other parts are low power, except for the panel drivers,
which themselves may be part of the panel!


Got to be careful. I've designed a HV generator with CCFL transformers
for a client last year. Guess who was the first one it bit?

The remainder of those TVs is often largely high integration. DSPs,
special video chips, memory, FPGA, ASICs. Very hard to debug because
they won't give you any technical documents, usually.

--
73, Joerg