Topics

The 434


dhuster@...
 

I'll start a new thread since the 465M thing is getting a little
diluted with everything else ... I certainly haven't helped!

Yes, the 434 X1/X10 lamps were the worst, requiring complete removal
of the vertical board.

And the vertical sensitivity was also set up by gain-switching as
well as attenuator switching, and those low-ohm gain-setting
resistors (they were 5% carbon comp resistors) were always skewing in
value and were miserable things to replace.

The attenuators were always getting dirty.

The switching power supply in the <B500000 was a miserable, all
discrete transistor thing.

The casting screw that was under the cover in the line fuse
compartment was always coming loose and playing merry hell with the
mains power on the fuse while hitting against the chassis. The only
fix was to get your #2 Posidiv on it and twist that screw as hard as
you could. It was a 10-32, so you weren't going to break or strip
anything, but it had to be tight.

All the boards used BRASS 3-48 screws rather than the standard steel
4-40 that all the other scopes used. No magnetic screwdriver help
there for those tight places.

Were they going to use a connector or solder the interconnecting
wires onto the board? You never knew.

I got one 434 in from a customer, famous for their trenching
products, that sat on their machine shop floor. I kid you not ...
when you picked it up and held it at an angle, oil dripped from
inside. With the cover off, oil was EVERYWHERE. It was awful. It
was something that even a standard run through the wash cycle
couldn't get it all out. Boards had to come off, covers had to come
off, casting screws had to be loosened, ..... it was awful.

The only other scope that was almost as bad as the 434 was .... what
else? The 432. Luckly, they didn't make as many of those.

The 434 made me thing that Tek should have the rule that all new-hire
engineers, both electrical and mechanical, should have to work in a
service center for a couple of years before designing anything.

Dean


Steve B.
 

Greetings;

--- In TekScopes@y..., dhuster@p... wrote:
I'll start a new thread since the 465M thing is getting a little
diluted with everything else ... I certainly haven't helped!

The only other scope that was almost as bad as the 434 was ....
what
else? The 432. Luckly, they didn't make as many of those.
My 212 is the most exasperating Tek item I own. I no longer have any
expectation of it working properly. My T932 has had to go back to
the 'scope doc twice for P/S probs (Wasn't there a delayed version if
these T900s also?). Looks tho' like I got off light compared to these
432/434 "gems".


The 434 made me thing that Tek should have the rule that all new-
hire
engineers, both electrical and mechanical, should have to work in a
service center for a couple of years before designing anything.
Dean
That, and hire a really good materials specialist to talk them out
of "time bomb" engineering choices. I.E., Delrin, plastic's answer to
pot metal.

Rgds; Steve


dhuster@...
 

Steve, the T935 is the delayed-sweep version of the T932.

The T912/T921/T922 was plagued with a problem with the female
connector on the main board that connects to the power supply. It
was always developing cracked/cold solder joints. The cure was to
pull the supply out, suck the solder from every terminal of the
female connector on the main board and then resolder each, using high
quality 63/37 solder and a good iron. However, I've only seen the
problem with the three models listed above and not the T93x (why, I
don't know) or the T922R (its supply was separate from the main board
and connected with a ribbon cable). But it wouldn't hurt to check or
even redo even if you don't see a problem. Cracked joints are
sometimes difficult to see.

The 212's biggest problem was batteries. And their batteries were
larger in diameter than "AA" cells, although folks have success with
using "AA" NiCds in them. This day and age, I'd switch the eight
cells over to NiMH so that you don't get the self-discharge and
memory of the NiCds. I have (well, HAD until the batteries ruined
the scope during extended storage) that I built entirely from
defective parts (I had to make my own output board since those NEVER
went bad. The vertical/timebase/trigger board on the side that I
used had no fewer than 8 open runs, some on the inner layer that
connected to rotary switch contacts through blind vias. Had to
trench and lay a wire in between contacts on the switch and carefully
solder to the edge of the contact where the wiper didn't travel,
being careful not to wet the rest of the pad, then epoxy over the
wire and smooth everything out. When I got done, the scope worked
great until it went into long-term storage.

Dean


Steve B.
 

Thanx Dean;
--- In TekScopes@y..., dhuster@p... wrote:
Steve, the T935 is the delayed-sweep version of the T932.

The T912/T921/T922 was plagued with a problem with the female
connector on the main board that connects to the power supply. It
was always developing cracked/cold solder joints. The cure was to
pull the supply out, suck the solder from every terminal of the
female connector on the main board and then resolder each, using
high
quality 63/37 solder and a good iron.
The ole "ringed joint" syndrome. I'll have to look at that again to
be sure it isn't an ongoing prob here.

The 212's biggest problem was batteries. And their batteries were
larger in diameter than "AA" cells, although folks have success
with
using "AA" NiCds in them. This day and age, I'd switch the eight
cells over to NiMH so that you don't get the self-discharge and
memory of the NiCds. I have (well, HAD until the batteries ruined
the scope during extended storage) that I built entirely from
defective parts (I had to make my own output board since those
NEVER went bad.
Yup, my expensive TEK replacement ni-cads whizzed into the PS board a
scant 2 years after installation. Still worked off ext 12V supply
after clean-up, but I wouldn't bet the farm on long-term reliability
now.

The vertical/timebase/trigger board on the side that I
used had no fewer than 8 open runs, some on the inner layer that
connected to rotary switch contacts through blind vias.
Thanx! This explains the intermittents neither myself or Bob Garcia
could nail down, primarily shielding probs.
I've pretty much now decided to retire it to the "cute li'l thingies"
shelf anyway. I'll just keep the others going and use the 310A for
the portable utility 'scope and the T932 for the bench, the 561,4,&5
for special projects.

Best; Steve


dhuster@...
 

Steve,

Since you rementioned intermittents (my mind was on the T900s and not
the 212) that reminds me of a very common source of intermittents in
the 200-series. Where two boards interconnect, Tek used square pin
connectors. The female side of those connectors had a loose, gold-
plated leaf spring that actually made the friction contact with the
male end. Often, this little leaf wind up missing somehow -- ZAP!
Intermittent connection -- and replacing the female connector would
fix the problem.

I usually didn't have trouble with the 200-series. I made
the "mistake" of seeing a group of them on the incoming shelf at the
Dallas Service Center and repaired them all fairly quickly. Pat
Morrison quickly "knighted" me as Sir 200-series and I ended up
repairing any of the little guys that came in the door, especially
after one fairly new tech spent two weeks destroying a 221. My job
was to repair that 221 no matter what and after $1800 of labor and
parts (the cost of a new 221 and was the other tech's time plus mine,
which was severely cut back to around $300 for the customer), it was
finally working again.

Other than the more rare 213, the 221 was the most difficult of the
baby scopes to work on. With no exception, you'd get one repaired
and calibrated, put it back in the case and it wouldn't even power
up. Take it back out of the case and turn it on and it was fine.
Put it back in the case and it would be fine. No explanation. It
finally got to where I'd repair and calibrate a 221, put it in the
case, not even bother to turn it on, then take it out of the case,
then put it back and THEN turn it on for its final check.

The 200-series' Achilles Heel was their CRT. It used a filament
rather than a heater to save on battery power, and that filament was
sooooooo delicate. Customers thought, "cute little football" and
tossed it around a little too roughly and would open the filament in
the CRT. In 1976, that was a $240 mistake just for the jug alone.
The other problem they had was the fact that customers always
thought, "little scope, little repair bill". A 212 or 221 nearly
always had the same size repair bill as a 465.

Dean