Re: 7603 weirdo inverted Z axis

On 23 Jan 2016 10:45:22 -0800, you wrote:

Hi David,

The sweep gate rises at the base of U99B to redirect the current from
the intensity control through the emitter of U99B to the collector.
The intensity is controlled by this current. If the -15 volt
connection to the intensity potentiometer is open, then the current
would *increase* as it is turned counterclockwise lowering the
resistance between the wiper and ground reversing its operation. The
intensity control range would also be affected but this might not be
very noticeable if the grid bias was adjusted.
Though it looks like this, I think that the CRT will simply remain dark. With the wiper at 0 V the CRT should definitively be dark. An extra resistance to 0 V will decrease the current to U99B and reduce the intensity which was already at dark. IIRC there are other scopes in which the wiper actively pulls a voltage or current higher and lower (and the current to the wiper changes direction). In that case the effect of an open connection can be different.
You're going to make me break out my Clipboard, aren't you?

One thing I wondered about the z-axis logic shown in the 7603
schematics is if the schematics were drawn wrong but I checked the
other 76xx series service manuals and they are all identical.

The gate signal is generated by an active pull-up from the horizontal
plug-in and its level is about +5 volts. That produces about 1.25
volts at the base of U99B and 0.6 volts at the emitter of U99B which
will be sufficient to turn U99B completely on and U99A completely off.
The voltages shown in the 76xx schematics are present when the gate is
off.

With -15 volts missing at the 5 kilohm intensity potentiometer, the
current through the emitter of U99B will vary from 0.6V/3k to 0.6V/8k
or 200uA to 75uA and increase as the intensity control is turned
counter clockwise.

Under normal conditions, the current will vary from 0.6V/3k to (0.6V +
15V)/8k or 200uA to 2.0mA and increase as the intensity control is
turned clockwise. That range of 1:10 had to be a deliberate design
criteria.

Is 200uA to 75uA enough to unblank the display and cause an adjustable
change in intensity? I did some of the calculations for the current
at the emitter of U99C and it looks to me like the intensity
adjustment will definitely be active and working from 200uA to 75uA if
the grid bias is adjusted appropriately.

So instead of checking to see if the intensity potentiometer is
connected backwards, check to see if the -15 volt supply is present at
the intensity potentiometer and that the wiper actually moves between
0 and -15 volts as the control is turned through its full travel
range. Note that -15 volts is suppose to produce the highest
intensity and 0 volts is suppose to produce the lowest intensity.

Sure that's the first thing to check anyway. I thought this would have been done already as part of checking for a cabling faults.

Albert
Public only stated that cabling was not an issue unless I missed
something and if the potentiometer was open between the -15 volt lead
and the element, then the only way to verify it would be to measure
the wiper voltage.

Re: Tektronix 555 problem

zerousair

Morris, I am copying below my last post tonight from the Antique Radio Forum. A couple of the fellows there have been trying to help fix my 555 also. Yes, the bad 21 TB is in the position for the upper beam. I have flat lines from both the sawtooth and gate connectors on the front of the bad 21 TB. Thank you for your time and help.

Garrett

"Worked on it more this aft. Set all switches on bad 21 TB as per TB trigger schem. and TB Generator type 21 schem. in manual no. 070-165. That's the one from BAMA and is from 1962. Mine is from 1959 and has no waveforms or voltages referenced to the stability control setting like the '62 manual. I injected a good square wave from the calibrator into the ext. jack on the bad 21 TB and got good amplification through V24, trigger input amplifier. Same good signal was applied to the grid, pin 2, of V45A. But the amplitude of the square wave was reduced more than half at the plate, pin 1, of V45A. I had +224 dc on the plate, pin1. +84 dc on the cathode, pin3. And +74 dc on the grid, pin 2. This confused me as I would have expected some amplification of the signal with those bias voltages? But put the extender on the good 22 time base and it read exactly the same voltages with all switches set the same. Of course, there is no trigger pulse waveform at pin 2 of V135A as per the type 21 time base unit schem. Flat line. Seems to me the problem is at V45, the trigger multivibrator. While moving time/cm on the bad 21 TB I got a sweep momentarily one time, but just one. Took out the 21 TB and used contact cleaner/lube on all switches. This is the good stuff and I used it for many years on control heads on Boeing and Airbus. Retired airline mech. since 2014. Have searched the internet looking for a good used 21 TB with no luck. If any of you fellows know of a source for one, I'd sure like to hear of it. Bored everyone enough with this, I reckon, but it's got me stumped."

Re: TDS754A printer compatibiliy

Tothwolf

On Sat, 23 Jan 2016, edbreya@... [TekScopes] wrote:

Thanks Tothwolf, I found one of my printers is an HL-2070N, and it worked right off the bat with the output printer type set to Laserjet. This may be the only one that takes PCL and has a Centronix port, so I'll have to take good care of it. I'm hoping I have another one of these buried somewhere.

I thought you mentioned in your other post that you had some maintenance info on these. If so, I'd sure appreciate anything you can send me.
I've emailed the files to directly to you off-list. These are great printers for single sided black-only printing and can do 1200 dpi at 20ppm. Brother rates the drums for these printers at 15k pages, although I've taken some up to 20-25k pages before needing to replace them. Aftermarket drums are available in the \$10-14 range. A complete refill of the toner cartridge can cost as little as \$5 or less and is good for 2500+ pages.

466 +15 supply and U1724 (1458)

jbaydcoid@...

Just got a 466 that was described as 'working then just quit' several years ago. All voltage measure slightly low but the +15 is way down to 1.4V. Unregulated +15 is slightly high 25.9 vs 22.5 presumably because of no current through pass regulator Q1756.

Looking at U1724B which regulates +15 the +input is 4.5 vs spec 15. Output is 1.5 vs 16.8. - input is 1.4 vs 15.

Interesting the other half U1724A both inputs are 4.5 should be 8.9. Output 5.1 should be 8.3. And the Vcc is also 4.5. The reference voltage from VR1726 is correct enough at 9.3.

Is it possible that the 10uf cap to ground at the + input is bad pulling that input down?

How does that relate to the low Vcc?

Thanks. Obviously I'm jet learning op amps.

John

Re: TEKTRONIX 260-1421-00 Switch, Beam Finder

Chris Pierce

Thanks I just ordered the switch from Qservice on their E bay store. I didn't even think of Ebay. Thanks for the help !!!

Re: TDS754A printer compatibiliy

Tothwolf

On Sat, 23 Jan 2016, Dwayne Verhey tekscopes@... [TekScopes] wrote:

Or you could connect a newer USB printer to your legacy equipment with one of these:

http://www.ipcas.com/products/centronics-parallel-to-usb-printer.html
The HL-2040 has both a parallel and a USB input.

The problem with using the Brother HL-2040 with the TDS754A is that the HL-2040 only works in GDI mode, which I guess the TDS754A can't use. I suppose it might be possible to use something to convert from PCL to GDI, but doing so would require the use of some sort of small computer. Probably just easier to save a GDI only printer for use with Windows/Mac/Linux and use a PCL compatible printer with the TDS754A.

Re: Tektronix 555 problem

Morris Odell

I assume you have a type 21 timebase in the upper beam slot and you can't
get it to sweep at all. Have you tried adjusting the stability screwdriver
pot? What is the "ready" light and the other neons in the timebase doing? If
you try to trigger it from the line, are there pulses coming out of the

Coincidentally I have just had to repair my 555 and, as ever, am amazed at
what a great performer it is - lovely sharp traces and easy & flexible
triggering in a nearly 60 year old scope. In my case the symptom was extreme
trigger jitter in both time bases. Checking the power supplies I found right
voltages but enormous ripple on the +500 supply. The fault was C760, a dual
40 mfd 450 volt electrolytic that filters the +150 that's stacked on top of
the +350 to make +500. I had a dual 50 mfd 350 volt cap to replace it and
now it's a good as new. Waiting for the relay to pull in the first time
after replacing a cap in a high energy circuit is not for the faint hearted!

Morris

----------------
The upper beam on this scope will only sweep unless set to trigger from
the lower beam time base. I can only get a dot with the upper beam set to
the (A) upper time base. Both time bases are set the same for recurrent. I
have tested all the upper time base tubes and all good. The supply voltages
checked as per the Tek schem. for the time base seem to be fine. There is a
"sawtooth out" jack on the front of the upper time base and from what I'm
seeing using the working trace, there is no sawtooth waveform there. I only
have this scope to check that with. Before I dig into it further, thought
I'd ask you fellows here if you've had any experience with this. Been many
years since I've worked electronic problems. I do have a time base extender.
Thank for any time and advice.

Garrett

Re: TDS754A printer compatibiliy

Torch Fireman

Here's another interesting approach, but you have to make your own cable:

http://www.printcapture.com

On 23/01/2016 3:54 PM, edbreya@... [TekScopes] wrote:

Thanks Tothwolf, I found one of my printers is an HL-2070N, and it worked right off the bat with the output printer type set to Laserjet. This may be the only one that takes PCL and has a Centronix port, so I'll have to take good care of it. I'm hoping I have another one of these buried somewhere.

Re: TDS754A printer compatibiliy

Torch Fireman

Or you could connect a newer USB printer to your legacy equipment with one of these:

http://www.ipcas.com/products/centronics-parallel-to-usb-printer.html

On 23/01/2016 3:54 PM, edbreya@... [TekScopes] wrote:

Thanks Tothwolf, I found one of my printers is an HL-2070N, and it worked right off the bat with the output printer type set to Laserjet. This may be the only one that takes PCL and has a Centronix port, so I'll have to take good care of it. I'm hoping I have another one of these buried somewhere.

Re: TDS544A status

Ed Breya

I managed to get a pretty good setup going. I happened to have an old rack-mount, slide-out LCD VGA station on hand that I got for free a while back. When opened up, it perches perfectly on top of the 544A. The native 640x480 VGA is also a perfect fit and gives a nice big-screen scope look that can be seen from across the room. It's a little awkward working the menu buttons since the display isn't physically associated with the button locations, but I can get used to it. The built-in laptop style keyboard isn't needed of course, but the deck makes a nice tray for paperwork or small items.

Ed

Re: TDS754A printer compatibiliy

Ed Breya

Thanks Tothwolf, I found one of my printers is an HL-2070N, and it worked right off the bat with the output printer type set to Laserjet. This may be the only one that takes PCL and has a Centronix port, so I'll have to take good care of it. I'm hoping I have another one of these buried somewhere.

I thought you mentioned in your other post that you had some maintenance info on these. If so, I'd sure appreciate anything you can send me.

Ed

Re: 7603 weirdo inverted Z axis

Albert Otten

Hi David,

The sweep gate rises at the base of U99B to redirect the current from
the intensity control through the emitter of U99B to the collector.
The intensity is controlled by this current. If the -15 volt
connection to the intensity potentiometer is open, then the current
would *increase* as it is turned counterclockwise lowering the
resistance between the wiper and ground reversing its operation. The
intensity control range would also be affected but this might not be
very noticeable if the grid bias was adjusted.

Though it looks like this, I think that the CRT will simply remain dark. With the wiper at 0 V the CRT should definitively be dark. An extra resistance to 0 V will decrease the current to U99B and reduce the intensity which was already at dark. IIRC there are other scopes in which the wiper actively pulls a voltage or current higher and lower (and the current to the wiper changes direction). In that case the effect of an open connection can be different.

So instead of checking to see if the intensity potentiometer is
connected backwards, check to see if the -15 volt supply is present at
the intensity potentiometer and that the wiper actually moves between
0 and -15 volts as the control is turned through its full travel
range. Note that -15 volts is suppose to produce the highest
intensity and 0 volts is suppose to produce the lowest intensity.

Sure that's the first thing to check anyway. I thought this would have been done already as part of checking for a cabling faults.

Albert

Re: Tektronix 2445B help

Albert Prat

Dave,

Thank you for the reply, I finally got a manual with the schematics section yesterday.

Best regards

Albert

From: TekScopes@... [mailto:TekScopes@...]
Sent: Friday, January 22, 2016 4:09 PM
To: TekScopes@...
Subject: Re: [TekScopes] Tektronix 2445B help

Albert

We have it including the separate Options service manual

http://artekmanuals.com/manuals/tektronix-manuals/

Enter 2445B in the searcxh box

Not free but not insulting either, high quality scans

Dave
ArtekManuals.com

On 1/22/2016 7:06 PM, aprat@... [TekScopes] wrote:

I have a 2445B that stopped working and need a set of shematics, I
have the 2445 service manual but it is very different and the only
2445B manual I could find on line does not have the schematics
section. Can anybody help? Thank you.
Albert

[Non-text portions of this message have been removed]

--
Dave
Manuals@...
www.ArtekManuals.com

Re: Tektronix 2445B help

Albert Prat

Thank you for the reply, I managed to get a service manual with schematics.

Best regards

From: TekScopes@... [mailto:TekScopes@...]
Sent: Friday, January 22, 2016 4:23 PM
To: TekScopes@...
Subject: Re: [TekScopes] Tektronix 2445B help

Based on the dates, the 2465B may be very similar if not mostly
identical.

On 22 Jan 2016 16:06:09 -0800, you wrote:

I have a 2445B that stopped working and need a set of shematics, I have the
2445 service manual but it is very different and the only 2445B manual I
could find on line does not have the schematics section. Can anybody help?
Thank you.
Albert

Re: TEKTRONIX 260-1421-00 Switch, Beam Finder

Malcolm Hunter

On 23 January 2016 at 15:18, piercec99@... [TekScopes] <
TekScopes@...> wrote:

Hello everyone, I'm not sure if I am posting this in the right place. If I
am in the wrong place please correct me. But I need a beam Finder switch
for a 2445 scope the part number is TEKTRONIX " 260-1421-00 " I think any
beam finder switch for any 2400 scope would work. Please someone Email me
at piercec99@... or message me here. Thank you all !!!
â€‹Have you tried ebay or Qservice? I can see the switch is available on both
sites.

Malcolmâ€‹

[Non-text portions of this message have been removed]

TEKTRONIX 260-1421-00 Switch, Beam Finder

Chris Pierce

Hello everyone, I'm not sure if I am posting this in the right place. If I am in the wrong place please correct me. But I need a beam Finder switch for a 2445 scope the part number is TEKTRONIX " 260-1421-00 " I think any beam finder switch for any 2400 scope would work. Please someone Email me at piercec99@... or message me here. Thank you all !!!

Re: Test 04 Fail 02

Christoph

I turned to a new attempt repeating the CAL cycles to get rid of that
Test 04 fail 02 condition when powering up the scope.

Just went through CAL01 and still have this error. Do I have to go through all the cycles in ordered sequence or may I possibly skip one cycle and enter one that is more likely responsible for the fail condition?

Maybe I should mention that I obtained a preprogrammed Dallas NVRAM chip from that greek firm (QService) which contains calibration data for a 2465B (mine is a 2445B).

Not that some preprogrammed data now conflicts with my entered data so far.

I also have an empty "new" empty Dallas DS1225. Should I rather start with that to rule out any conflict with pre-existing data?

--
Christoph

Re: 7603 weirdo inverted Z axis

There are some ways you can narrow down the problem before tracing the
z-axis control circuits:

1. Does the readout intensity control also operate backwards?

Its signal goes directly to the readout board which then drives the
input to the z-axis amplifier in parallel with the normal intensity
signal so it bypasses all of the z-axis logic.

2. Plug-ins can also adjust the beam intensity. If you have a 7B92A
timebase, what does its intensity control do?

3. Is the leading edge unblanking working correctly when a fast pulse
edge is observed?

I checked my 7603 and with a 7B53A timebase, about 1/2 division at 50
ns/div (25 nanoseconds) is unblanked before a fast pulse edge. With a
faster timebase like a 7B92A, 1 full division at 50 ns/div (50
nanoseconds) is unblanked before a fast pulse edge. Oddly enough a
7B50A also unblanked 50 nanoseconds before the fast pulse edge so I
assume it shares more in common with the faster timebases than the
7B53A.

As far as tracing the circuit, the z-axis amplifier is straightforward
but the z-axis logic shown on schematic 2 gives me a headache. I will
have to break out Clipboard CAD to figure out exactly what is suppose
to be happening there. I do see one thing however:

The sweep gate rises at the base of U99B to redirect the current from
the intensity control through the emitter of U99B to the collector.
The intensity is controlled by this current. If the -15 volt
connection to the intensity potentiometer is open, then the current
would *increase* as it is turned counterclockwise lowering the
resistance between the wiper and ground reversing its operation. The
intensity control range would also be affected but this might not be
very noticeable if the grid bias was adjusted.

So instead of checking to see if the intensity potentiometer is
connected backwards, check to see if the -15 volt supply is present at
the intensity potentiometer and that the wiper actually moves between
0 and -15 volts as the control is turned through its full travel
range. Note that -15 volts is suppose to produce the highest
intensity and 0 volts is suppose to produce the lowest intensity.

On Fri, 22 Jan 2016 20:18:20 +0100, you wrote:

Among other issues with this 7603 were the Z axis operation, it seemed
like a blanking issue (beam is not blanked correctly), but on closer
inspection it is a bit more involved:

The intensity control works reversed (fully CCW is maximum intens, fully
CW blanks the beam). This is not a cabling issue.

Blanking signals are correctly processed by the Z axis logic, and the Z
axis amplifier produces the correct voltages on pin B (about 20 V with
P1171 open for a blanked beam, and about 90 V with maximum input current
for maximum intensity). I also cross checked this against a working 7623
just to be sure that I analyzed the circuitry correctly and understood
the circuit description.

So the inversion must happen somewhere else. I previously replaced all
HV caps in the HV unit, including the DC restorers. Now I also replaced
all diodes in the grid DC bias restorer. No change in behaviour.

The focus amplifier, preset and front panel control all work correctly.

I don't know what else I could check or what else could cause this.
Maybe someone here has another idea?

Cheers,
Marian

Re: Tek 555 service manual.

zerousair