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