I found a source of the DM44 manual on CD ($14) or for download
($10). I used the manual to fix my DM44 problem which turned out to
be a bad 7474 D-type flipflop. The person running this site is
working to have most of the Tek manuals and is scanning them with
new equipment now. Prices are quite reasonable. (Note: I have no
affiliation with the owner of the site or his business other than
being a satisfied customer).

Here is the link: http://www.aa4df.com


Al
--- In TekScopes@yahoogroups.com, "Al Testani" <atestani@a...> wrote:

I was about to post the same request. Is there a service manual
including schematics for the DM44?

--- In TekScopes@yahoogroups.com, "firmecivic" <rgutierrez@t...>
wrote:

Does anybody have an adjustment procedure for the DM44 or could
somebody tell me which pots controll what? Any help is

appreciated!

Hi all
I need a working acquisition board for a TDS540A or 544A.
Anyone have a dead unit they wish to sell for parts ?
If so, send me your details and price (or swap for other items you need).
Regards
Denis Cobley

BTW, one of those BB's was cracked!

stan

On the 310, there are three black-beauties soldered to the trace-side of the HV board. I cannot see any identifications as to capacitor numbers. These are all rated for 3 kV and the values are 0.015 uF, 0.0068 uF, and 0.0068 uF. After learning the hard way, I know better than to assume willy-nilly that a bigger bypass is better across the board. I have 0.033 uF/3kV caps in-hand, and I'm betting that I can replace the 0.015 uF unit with no problem. However, are the 0.0068's value-critical? Are these part of the oscillator timing circuitry? I have a 310 A schematic, but not a 310, which is why I am wondering.

Thanks.

stan

Hi,

I asked in this group some while ago for a source for a 7854 manual in
electronic format (pdf).

One of the other sources where I enquired was Teknetelectronics, who at
that time didn't have one available. In response to my request they have
now provided a copy, which can be had from the following FTP site:-

ftp://www.teknetelectronics.com/Manuals/TEK-7854-OM.pdf

Regards,
Harry
M1BYT@GB7FCR.#16.GBR.EU
harry.m1byt@tiscali.co.uk

Interested in Amateur Radio?
http://www.ukradioamateur.org/

Hmmm... don't know what happened to my earlier follow up post,
so I'll post again.
The problem was a broken wire/coil feeding the base of Q1338.
The wire is wrapped twice through a ferrite bead. It broke,
and contacted the 100v trace. Q1338 and Q1332 were blown.

I was able to solder the broken wire, thus retaining the
original ferrite coil. I can't locate that coil in the
(blurry) schematic.

For Q1338, I used an unmarked NPN silicon from the junk
box. Another junk box xsistor, marked 5401, was used for
Q1332.

My parts questions:
1) Q1338 is marked TI 811 - does anyone know the correct
equivalent?
2) Q1332 is marked FPN 3640 - same question as above.

Thanks,
Ed

I will look further into this and other circuity around U370 since
swapping out U370 did not change the symptoms of this problem! The
input side of U370 looks fine (measuring differentially with another
scope) whereas the output has the problem. There isn't much around
U370 that looks like it could be doing this, however.

What about the channel switch logic, U350? I've had failures in old TTL
before, and if the level-shifted waveforms into pins 1, 16, 13 and 12 are
out of whack, it could be only partially turning on the switch transitors in
the hybrid, leading to non-linear response.

Just a thought

Craig

Hopefully you decoded my horrendous typo to mean Delay Line DC
Centering.

Yes, it is adjustable and is a pot in the circuit right after the
bandwidth limiting circuit. Per the service manual, the procedure
is to put a DVM across the delay line conductors on the delay
line "input" side (i.e. the side closest to U370) and adjust the
vertical position control so there is zero volts across them. Then
measuring from chassis ground to either delay line conductor, adjust
the delay line centering control for 0 volts. It didn't seem to have
any effect on the problem.

I will look further into this and other circuity around U370 since
swapping out U370 did not change the symptoms of this problem! The
input side of U370 looks fine (measuring differentially with another
scope) whereas the output has the problem. There isn't much around
U370 that looks like it could be doing this, however.

--- In TekScopes@yahoogroups.com, "John Miles" <jmiles@p...> wrote:

Delay line DC cneter ing is set to about 1mV of
chassis ground.

What exactly is this parameter? Is it adjustable? Sounds like

there's a

way to adjust the linearity or bias on U370, and it's out of whack.

-- jm

Sorry, a reply to my reply to my own post!

I swapped out the channel switch hybrid (155-0091) and the

problem

remained the same! i.e. the hybrid is fine.

Delay line DC cneter ing is set to about 1mV of
chassis ground.

What exactly is this parameter? Is it adjustable? Sounds like there's a
way to adjust the linearity or bias on U370, and it's out of whack.

-- jm

Sorry, a reply to my reply to my own post!

I swapped out the channel switch hybrid (155-0091) and the problem
remained the same! i.e. the hybrid is fine.

Sorry, a reply to my reply to my own post!

I swapped out the channel switch hybrid (155-0091) and the problem
remained the same! i.e. the hybrid is fine.

I'm stumped now... Anyone got any leads or tips that can get me
moving again toward solving this problem? Thanks!

--- In TekScopes@yahoogroups.com, "Al Testani" <atestani@a...> wrote:

replying to my own post with more information...

I think I have now traced the problem back to the main vertical
board. Using another scope to make a differential measurement

(i.e.

chan 2 inverted and function on Add), I can see an amplitude

change

vs vertical position at the output of the channel switch (U370)

but

not the input. Delay line DC cneter ing is set to about 1mV of
chassis ground. Since the problem is common to both vertical
channels, U370 is the first place the path becomes one. Looks

like

U370 is bad!!? Is this a failure mode of this part?

--- In TekScopes@yahoogroups.com, "Al Testani" <atestani@a...>

wrote:

Many thanks, John. Your help is very much appreciated!

I swapped the vert deflection leads and the problem reversed
directions as you predicted for a problem other than the CRT. I
guess it is good the CRT is OK <g> but now I am starting to

wonder

if one of those magic (proprietary) Tek ICs is at fault!

I've checked all the low voltages and they are right on. The

+15

DCPL and -8V DCPL on the vertical output board are also fine.

For what it's worth: the Y-align pot is sitting at about +1V and

the

Geometry pot is at about +50V. The vertical shield voltage is at
34.5V.

It looks dangerous probing around U470 at all the biasing

networks

so I haven't done that yet. Is that where I need to look next

or

is

there somewhere else to be checking? You also

mentioned "response"

in your previous reply. Not sure I understand that one as the
problem occurs with a DC input. What should be checked there?

Thanks again

Al


--- In TekScopes@yahoogroups.com, "John Miles" <jmiles@p...>

wrote:

If that's the case, yes. But you'd want to check the vertical

deflection

supply voltages and response first. That's the most likely

cause

of

trouble, and the easiest to fix. :)

An easy way to rule out the CRT would be to swap the

connections

to the

vertical deflection plates. If the nonlinear amplitude-versus-

position

behavior remains the same, then it's the CRT. If the waveform

now

becomes

taller when positioned near the top of the display, then it's a
deflection-amplifier problem.

-- jm

-----Original Message-----
From: Al Testani [mailto:atestani@a...]
Sent: Wednesday, October 01, 2003 10:08 AM
To: TekScopes@yahoogroups.com
Subject: [TekScopes] Re: Help Needed! 475A

Vertical "linearity"

So the fix is to replace the CRT!?!

Hi Geoff
These are the most accurate range of scopes Tek ever made!
Having said that, they are large units and a scope cart is a very useful
accessory.
We have several and generally they are reliable.
Parts are only available by cannibalising another unit as there is no
support from Tek.
Best test is to run the "Enhanced Accuracy" from the front panel (best if
all slots are filled with plug-in's).
If it passes this then the unit is in good operating condition.
If not then you can expect to need a donor unit for parts to repair it.
The main failure is Acquisition boards and fixing these is not a high
probability without a good working unit to swap parts into.
Even then you need good replacement parts.
Still - if it works you have a low cost 1GHz multi channel digital scope
with lots of features
Regards
Denis

Hi,

What's the general opinion of this series? How serviceable are they? Are there particular models to avoid?

Thanks,
Geoff

replying to my own post with more information...

I think I have now traced the problem back to the main vertical
board. Using another scope to make a differential measurement (i.e.
chan 2 inverted and function on Add), I can see an amplitude change
vs vertical position at the output of the channel switch (U370) but
not the input. Delay line DC cneter ing is set to about 1mV of
chassis ground. Since the problem is common to both vertical
channels, U370 is the first place the path becomes one. Looks like
U370 is bad!!? Is this a failure mode of this part?

--- In TekScopes@yahoogroups.com, "Al Testani" <atestani@a...> wrote:

Many thanks, John. Your help is very much appreciated!

I swapped the vert deflection leads and the problem reversed
directions as you predicted for a problem other than the CRT. I
guess it is good the CRT is OK <g> but now I am starting to wonder
if one of those magic (proprietary) Tek ICs is at fault!

I've checked all the low voltages and they are right on. The +15
DCPL and -8V DCPL on the vertical output board are also fine.

For what it's worth: the Y-align pot is sitting at about +1V and

the

Geometry pot is at about +50V. The vertical shield voltage is at
34.5V.

It looks dangerous probing around U470 at all the biasing networks
so I haven't done that yet. Is that where I need to look next or

is

there somewhere else to be checking? You also

mentioned "response"

in your previous reply. Not sure I understand that one as the
problem occurs with a DC input. What should be checked there?

Thanks again

Al


--- In TekScopes@yahoogroups.com, "John Miles" <jmiles@p...> wrote:

If that's the case, yes. But you'd want to check the vertical

deflection

supply voltages and response first. That's the most likely

cause

of

trouble, and the easiest to fix. :)

An easy way to rule out the CRT would be to swap the connections

to the

vertical deflection plates. If the nonlinear amplitude-versus-

position

behavior remains the same, then it's the CRT. If the waveform

now

becomes

taller when positioned near the top of the display, then it's a
deflection-amplifier problem.

-- jm

-----Original Message-----
From: Al Testani [mailto:atestani@a...]
Sent: Wednesday, October 01, 2003 10:08 AM
To: TekScopes@yahoogroups.com
Subject: [TekScopes] Re: Help Needed! 475A Vertical "linearity"


So the fix is to replace the CRT!?!

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Regards,
Michael Dunn
Listowner, TekScopes

It looks dangerous probing around U470 at all the biasing networks
so I haven't done that yet. Is that where I need to look next or is
there somewhere else to be checking? You also mentioned "response"
in your previous reply. Not sure I understand that one as the
problem occurs with a DC input. What should be checked there?

Sorry -- by "response" I meant the symmetry test, which you've just
performed.

Unfortunately I don't have a 475 manual handy... but your post reminded me
of a 485 I once owned with a similar problem. The CRT plates were so far
out of whack in that one that a sine wave would appear to travel backwards
in time during certain portions of the cycle!

In your case, it might make sense to follow a DC signal (flat trace) through
the deflection-amp chain with a DMM or another scope, working the position
control up and down to spot the stage where the nonlinearity occurs.

-- jm

Many thanks, John. Your help is very much appreciated!

I swapped the vert deflection leads and the problem reversed
directions as you predicted for a problem other than the CRT. I
guess it is good the CRT is OK <g> but now I am starting to wonder
if one of those magic (proprietary) Tek ICs is at fault!

I've checked all the low voltages and they are right on. The +15
DCPL and -8V DCPL on the vertical output board are also fine.

For what it's worth: the Y-align pot is sitting at about +1V and the
Geometry pot is at about +50V. The vertical shield voltage is at
34.5V.

It looks dangerous probing around U470 at all the biasing networks
so I haven't done that yet. Is that where I need to look next or is
there somewhere else to be checking? You also mentioned "response"
in your previous reply. Not sure I understand that one as the
problem occurs with a DC input. What should be checked there?

Thanks again

Al


--- In TekScopes@yahoogroups.com, "John Miles" <jmiles@p...> wrote:

If that's the case, yes. But you'd want to check the vertical

deflection

supply voltages and response first. That's the most likely cause

of

trouble, and the easiest to fix. :)

An easy way to rule out the CRT would be to swap the connections

to the

vertical deflection plates. If the nonlinear amplitude-versus-

position

behavior remains the same, then it's the CRT. If the waveform now

becomes

taller when positioned near the top of the display, then it's a
deflection-amplifier problem.

-- jm

-----Original Message-----
From: Al Testani [mailto:atestani@a...]
Sent: Wednesday, October 01, 2003 10:08 AM
To: TekScopes@yahoogroups.com
Subject: [TekScopes] Re: Help Needed! 475A Vertical "linearity"


So the fix is to replace the CRT!?!

If that's the case, yes. But you'd want to check the vertical deflection
supply voltages and response first. That's the most likely cause of
trouble, and the easiest to fix. :)

An easy way to rule out the CRT would be to swap the connections to the
vertical deflection plates. If the nonlinear amplitude-versus-position
behavior remains the same, then it's the CRT. If the waveform now becomes
taller when positioned near the top of the display, then it's a
deflection-amplifier problem.

-- jm

So the fix is to replace the CRT!?!

--- In TekScopes@yahoogroups.com, "John Miles" <jmiles@p...> wrote:

Unfortunately, it sounds like this scope might have been dropped.

The

vertical deflection plates may have been jarred out of alignment.

-- jm

I am trying to refurbish and calibrate a 475A I recently

purchased.

I have found that both vertical channels are "non-linear" in

gain.

What I see is this:

Input a calibrated 2cm high square wave that straddles the

vertical

centerline and then use the vertical position control to move the
waveform to the bottom of the screen and then to the top. At the
bottom two cm the waveform is greater than 2cm and at the top 2

cm

it is less than 2cm. In each case it is off between 0.1 and 0.2

cm.

This problem occurs with a 1KHz square wave or with a DC input.
IOW, the gain appears different depending on the vertical

position

control setting!

Both channels are doing this and with inputs from various

sources.

The Variable balance and V/div balance are set very close as are

the

DC centering and 5mV and 10mV gain adjustments.

Any help on this would be greatly appreciated! Thanks!!

Unfortunately, it sounds like this scope might have been dropped. The
vertical deflection plates may have been jarred out of alignment.

-- jm

I am trying to refurbish and calibrate a 475A I recently purchased.
I have found that both vertical channels are "non-linear" in gain.
What I see is this:

Input a calibrated 2cm high square wave that straddles the vertical
centerline and then use the vertical position control to move the
waveform to the bottom of the screen and then to the top. At the
bottom two cm the waveform is greater than 2cm and at the top 2 cm
it is less than 2cm. In each case it is off between 0.1 and 0.2 cm.
This problem occurs with a 1KHz square wave or with a DC input.
IOW, the gain appears different depending on the vertical position
control setting!

Both channels are doing this and with inputs from various sources.
The Variable balance and V/div balance are set very close as are the
DC centering and 5mV and 10mV gain adjustments.

Any help on this would be greatly appreciated! Thanks!!

Al