开云体育

Let me know if you have questions about the histogram program. Although it has been a mere 40years, I might be able to remember how and why I did certain things.

I have identified that Q913 is short circuit between E,B&C and I also
suspect Q923, but until I get them out that's as far as I've got.

Shorted Q913 could cause what you saw. However, did you measure it in place or after disconnecting from the circuit?

Someone suggested I check C914 - I know its 15uF but do you know the
rating ??

All component information is in the service manual. Section 8-9 (Page 113 in the PDF I am looking at) shows 15uF, 20%, 63V. I don't see why it would cause this issue after a knock but now all the components (including caps) did exceed their expected voltage by a large margin so they could be damaged. For example C971 is rated 50V but was stressed to 63V. Some components will survive brief over voltage, some may be damaged. In particular ICs may go into "latch up" and draw excessive current.

Ozan


Ozan

I have identified that Q913 is short circuit between E,B&C and I also suspect Q923, but until I get them out that's as far as I've got.

I cannot see any bulging caps or burnt components, damaged traces or other obvious issues and I've looked very closely.

Someone suggested I check C914 - I know its 15uF but do you know the rating ??

Thanks for the tips.

I'm just concerned for the cause - it wasn't powered when knocked.
Perhaps it's just coincidence and it was a fault just in waiting ;-)

Dave

Thanks Jeff.

Why did the open filter capacitor destroy the 741s? Surely open filter capacitors is a problem the tester should identify and not itself fail from.

Larry

--
Best wishes,

Larry McDavid W6FUB
Anaheim, California (SE of Los Angeles, near Disneyland)

I came across this, and thought it would interest people here.

I resolved the problem. My confusion was cased by the Tek 070-1304-00 August 1974 manual for the TM501 found on TEKWIKI. This earlier manual shows Q10 on the left and Q12 on the right. The later 070-1304-01 June 1985 revision found on BAMA agrees with the configuration of my unit. Either the earlier TM501 units were configured differently or the original Tek documentation was in error.

It turned out the 2000 uFd filter capacitor for the +33.5V supply was completely open, causing the TM501 to output a half-wave rectified waveform. This destroyed the 741 op amps in both 15V supplies. I installed sockets for the replacements.

This exercise impressed me with the importance of testing these aged frames before plugging-in valuable modules. Fortunately, I did not try and use this one until now. My thanks again to Jared Cabot for this useful tool.

Bruce, KG6OJI

Oh yess!!!
Thank you folks! The scan you pointed on tekwiki is definitely more, more readable!
Thank you again,
Max

Thanks, Dennis and good luck to your wife. My experience: I had my right hip replaced in October of last year, due to arthritis. I am 67. I spent a week in the hospital and two more in a rehab facility. I was walking unaided after the first week, though my cane helped. The physical therapists helped my adjust my gait and to deal with stairs. The incision was painful then especially if I bumped it getting out of the hospital bed. Now I feel my hip is perfect and can consider going some place on a walking tour. However my left leg is a big problem due to neurological damage 17 years ago. Fixing it has been futile but at least I can walk unaided. Back to the hip. There is still some pain at the incision site if I touch it - not excruciating though. The upshot: If you've been advised to have a hip replaced do it. I'm very happy I did.

Greg,

This is what the HP Accessory boxes looked like and this appears to be
the same kind of foam although it doesn't appear to be deteriorated. But
sometimes the foam that we encountered didn't appear to be deteriorated
either until we touched it.

<

Here is another HP Accessory box but the hinge on this one wore out and
the top of the box is missing. That is a very common problem with this
type boxes. Also the flex part of the front latch would wear out and the
latch would fall off. <
>
But this box has closed cell foam in it and I don't recall ever having
problems with that.

On Tue, Mar 16, 2021 at 12:11 PM Greg Muir via groups.io <big_sky_explorer=
[email protected]> wrote:

A couple of questions and comments.

I see you have indicated that there is a foam product present in the
container. Can you better describe the appearance of it to help define
what it is? Yes, there are foam products releasing agents that can cause
deleterious effects on metals and such.

What type of container are the plug-ins housed in? You mention that the
container is “…almost fully sealed…”. One must remember that through
ambient temperature changes air tends to expand and contract. This allows
any container that is not totally sealed to “breathe” and allow any
external humidity inside.

Is the foam being held in place by any adhesives? I once encountered a
waterproof transit case that had standard low density foam fastened inside
with an adhesive. Over time the contents of the case showed signs of
deterioration similar to what you are experiencing. It turned out that the
adhesive was releasing a product that caused the problem. And since the
container was totally sealed from any environmental effects the inside of
the case was a perfect chamber to contain the corrosive atmosphere.

Do you live in an area that has a relatively humid environment? While
working in the tropics I came upon an older piece of HP equipment that was
supposedly in “safe” storage but the room was not dehumidified. When I
picked it up there was heard rattling inside. Opening it up I found that
all of the discrete transistors had lost their gold plating (gold was
frequently used I those days to plate leads) and the moisture had attacked
the steel wire thereby corroding it to the point where there was no metal
left and the transistors simply fell off the printed circuit boards.
Obviously there were also signs of corrosion on other parts as well
including “worm tracks” on the anodized front panel where the moisture went
under the sealed anodic oxide surface and made very fine random tracks on
the raw aluminum as it made its way along.

Greg

PS, the HP Accessory boxes were one piece boxes and had a snap on the
front. All of it was in one piece,; both halves of the box, the hinge and
the snap. they fit together pretty well but they certainly weren't
airtight. It is humid here but the place that nearly all of our equipment
came from was a large US government facility and it was well air
conditioned so I think the items were kept inside in AC storage but I can't
say that for certain.

On Tue, Mar 16, 2021 at 12:11 PM Greg Muir via groups.io <big_sky_explorer=
[email protected]> wrote:

A couple of questions and comments.

I see you have indicated that there is a foam product present in the
container. Can you better describe the appearance of it to help define
what it is? Yes, there are foam products releasing agents that can cause
deleterious effects on metals and such.

What type of container are the plug-ins housed in? You mention that the
container is “…almost fully sealed…”. One must remember that through
ambient temperature changes air tends to expand and contract. This allows
any container that is not totally sealed to “breathe” and allow any
external humidity inside.

Is the foam being held in place by any adhesives? I once encountered a
waterproof transit case that had standard low density foam fastened inside
with an adhesive. Over time the contents of the case showed signs of
deterioration similar to what you are experiencing. It turned out that the
adhesive was releasing a product that caused the problem. And since the
container was totally sealed from any environmental effects the inside of
the case was a perfect chamber to contain the corrosive atmosphere.

Do you live in an area that has a relatively humid environment? While
working in the tropics I came upon an older piece of HP equipment that was
supposedly in “safe” storage but the room was not dehumidified. When I
picked it up there was heard rattling inside. Opening it up I found that
all of the discrete transistors had lost their gold plating (gold was
frequently used I those days to plate leads) and the moisture had attacked
the steel wire thereby corroding it to the point where there was no metal
left and the transistors simply fell off the printed circuit boards.
Obviously there were also signs of corrosion on other parts as well
including “worm tracks” on the anodized front panel where the moisture went
under the sealed anodic oxide surface and made very fine random tracks on
the raw aluminum as it made its way along.

Greg

Greg,

I don't remember if the foam in the HP boxes was glued in or if it was
cast in place but I thinnk it was glued in. But it was a very dark gray and
almost black color and it was an open cell foam with very tiny (~ 1/32")
cells. In the open areas where nothing had touched it the foam would look
fine until you touched and when you did, it just collapsed with no
resistance. It usually crumbled to a dark powder and you could wash most of
it out with soap and water but it always left a certain amount behind that
was nearly impossible to remove.

Besides that used by HP, i've also seen sheets of anti-static foam that
ICs were stored in and it did pretty much the same. It would just crumble
without being touched and it would attack the legs of the ICs and
occasionally completely eat them away from the IC body.

I will look around on the internet and see if i can find any pictures.

On Tue, Mar 16, 2021 at 12:11 PM Greg Muir via groups.io <big_sky_explorer=
[email protected]> wrote:

A couple of questions and comments.

I see you have indicated that there is a foam product present in the
container. Can you better describe the appearance of it to help define
what it is? Yes, there are foam products releasing agents that can cause
deleterious effects on metals and such.

What type of container are the plug-ins housed in? You mention that the
container is “…almost fully sealed…”. One must remember that through
ambient temperature changes air tends to expand and contract. This allows
any container that is not totally sealed to “breathe” and allow any
external humidity inside.

Is the foam being held in place by any adhesives? I once encountered a
waterproof transit case that had standard low density foam fastened inside
with an adhesive. Over time the contents of the case showed signs of
deterioration similar to what you are experiencing. It turned out that the
adhesive was releasing a product that caused the problem. And since the
container was totally sealed from any environmental effects the inside of
the case was a perfect chamber to contain the corrosive atmosphere.

Do you live in an area that has a relatively humid environment? While
working in the tropics I came upon an older piece of HP equipment that was
supposedly in “safe” storage but the room was not dehumidified. When I
picked it up there was heard rattling inside. Opening it up I found that
all of the discrete transistors had lost their gold plating (gold was
frequently used I those days to plate leads) and the moisture had attacked
the steel wire thereby corroding it to the point where there was no metal
left and the transistors simply fell off the printed circuit boards.
Obviously there were also signs of corrosion on other parts as well
including “worm tracks” on the anodized front panel where the moisture went
under the sealed anodic oxide surface and made very fine random tracks on
the raw aluminum as it made its way along.

Greg

I checked the DC recovery diodes in the HV supply as listed in other thread
(all under the plastic cover and they are ok.
Any other suggestions?

On Mon, 15 Mar 2021, 22:30 Ondrej Pavelka, <info@...>
wrote:

Hi folks,

I acquired some time ago 485 and finally today I managed to spend some
time with it.

Cleaning of the switches and moving all the controls back and forth
several times brought back most things so I could see both channels
working.

Most challenging was/is the

TIME base,
wouldn't scale correctly but after really many turns it now basically does
what it should with exception of the last 3 fastest settings. There the
picture is all to the side and slowly drifts in but it's very distorted and
quite clearly there's something wrong.

I can also see ghost signals like if there was massive jitter or even
better described some bounced signals as if the transmission wasnt
terminated and I think I can see the signal partly during blank phase.
Things are better at higher frequencies and worse on lower. When I enable
second time base it's only very faint picture only visible with B intensity
at max. But when I move the display all the way to the right I can see very
bright spots on the left side so maybe the horizontal signal doesn't have
proper connection somewhere and only deflection I can see is some
crosstalk?

power supply

all the low voltages look OK, but the high voltage 2950V I can only
measure some 2000 volts. It is my first time using 1000x probe for
multimeter so I have checked on my lab psu and 30V was correctly showing as
30mV. So it's likely the voltage coming from the multiplier is too low
unless the voltmeter impedance despite being so high could drop it down?
Brightness settings both total and B have basically no effect what so
ever. They do something but very fine adjustment only.

Fan isn't spinning, any replacement ideas?

Channel 2

1x LED doesn't work
The 1M/50Ohm illumination doesn't work
The 10x and 100x works ok
There was a tantalum in the ch2 attenuator 22uF/15V I replaced because it
had a head blown off but it didn't really change anything.
I tested around U80 and shorted the pins associated with lightbulb for
1M/50 and reset lightbulb and pin associated with 1x diode and it looks
like these are faulty because they don't light up and there is correct 5V
on the other side.

Overall the picture probably could be adjusted to be rather nice and sharp
if the brightness could be turned down and the ghost images resolved.
Appreciate if those who been through 485 before could give me some heads
up what to look at first and where to look to solve the issues.

P. S. It's got 7 small knobs missing, anybody happen to have some spare
parts donor?

Hi Dave,
I don't know if you already figured out the issue but in case you are still debugging: 63V at W972 translates to 48V at pin 12 of U940 which exceeds Abs Max of TL594. There must be other components that could be damaged permanently. In this state any powered up debug needs reducing the input voltage at pins 1 and 2 (input to pre-regulator) of sheet <7>, less than 55V but probably 45V is a good start. I would disconnect all the connectors to A1 board and supply external bench supply to pin 1 and 2.

Before doing electrical debug, I recommend visually look for broken solder junctions and reseat the ICs (if they are on a socket). Most likely in the pre-regulator section of sheet <7>.

If visual inspection doesn't show what is wrong electrical debug can identify the issue:
At 63V pre-regulator is not pulse width modulating the pass transistor or the load is too light. How does waveform (34) look like on sheet <7>?

Ozan

Hoping and praying that Mrs. Tillman will recover fast. We all take the other half for granted and this sort of thing makes us think hard! Take things slow and try not to get overloaded yourself.

That porosity is why gold flash is so useless; basically decorative.? For professional equipment, we always specified 30u" of Au, 15u" was the absolute minimum.? Flash was considered worse than no gold, and verboten.
-Dave

This scan is more legible than the others on the net:

Hi Max,

The PDF available on TekWiki is a very good quality scan:



At 400% magnification, the listing is quite legible.


dan

Hi all,
I am experimenting in programming the 7854 and I found this application note with very interesting programs, in particular the listing in figure 20, penultimate page.
Unfortunately it is quite (almost completely to be honest!) unreadable.
Any of you friends of TekScopes, do you have a readable copy?
If yes can you post the listing of figure no. 20? There are 77 program lines.

Thanks in advance,
Max

All the best to you and Marian.

If you have a 555 scope, you might be able to combine Tek along with feeding the fold by baking bread on top of it!

Thanks,
Barry - N4BUQ