Date   
Re: 7603 weirdo inverted Z axis

Albert Otten
 

Good info Marian, this makes all discussions about intensity pot and Z axis logic superfluous.
An easy explanation would be that the polarities of both diodes CR1269 and CR1270 are reversed. That doesn't do any harm to that circuit but produces the effect you describe.

Albert



---In TekScopes@..., <public@...> wrote :

On 01/22/2016 10:11 PM, aodiversen@... mailto:aodiversen@... [TekScopes] wrote:
> Hi Marian, do I understand you correctly if I think that the Z amplifier
> itself is working correctly but that the CRT gets brighter when the Z
> output at B gets lower (less positive)? In that case I have no idea
> what's going on, but then you should also "complain" that the Readout is
> shown as negative image.
> If the Readout is correct then the logic board is suspect, for instance
> a faulty U99.
>
> Albert

Albert, yes this is what I am thinking. If I remove all inputs to the Z
axis amplifier it outputs about 20 V, which should blank the beam - but
doesn't. Shorting the input to ground, i.e. full input current, produces
approx. 90 V at the output (pin B), which should produce full intensity
- instead it blanks the beam.

Re: 7603 weirdo inverted Z axis

Marian B
 

On 01/22/2016 10:11 PM, aodiversen@... [TekScopes] wrote:
Hi Marian, do I understand you correctly if I think that the Z amplifier
itself is working correctly but that the CRT gets brighter when the Z
output at B gets lower (less positive)? In that case I have no idea
what's going on, but then you should also "complain" that the Readout is
shown as negative image.
If the Readout is correct then the logic board is suspect, for instance
a faulty U99.

Albert
Albert, yes this is what I am thinking. If I remove all inputs to the Z
axis amplifier it outputs about 20 V, which should blank the beam - but
doesn't. Shorting the input to ground, i.e. full input current, produces
approx. 90 V at the output (pin B), which should produce full intensity
- instead it blanks the beam.

On 01/22/2016 10:11 PM, aodiversen@... [TekScopes] wrote:
In that case I have no idea
what's going on, but then you should also "complain" that the Readout
is shown as negative image.
I don't think it would work this way, since the readout uses vectors to
display the text, fiddling with the Z axis would only change the beam
current, while the beam still traces the same characters.

On 01/23/2016 06:41 AM, David @DWH [TekScopes] wrote:
1. Does the readout intensity control also operate backwards?
The readout board in this unit was shot (1 simple ASIC missing, at least
2 ROMs dead), I replaced it by a known-working board yesterday. Readout
works just fine, but like the other intensity control the readout
intensity control works backwards.

3. Is the leading edge unblanking working correctly when a fast pulse
edge is observed?
If I adjust intensity so that I can see the beam it is never blanked.
When retrace / wait for sweep occurs the Z axis logic produces a low
current (high voltage, turning Q1107 off), which leads to ~20 V from the
Z axis amplifier output, which should blank the beam, but instead the
beam turns all the way up.

On 01/23/2016 06:41 AM, David @DWH [TekScopes] wrote:
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.
Yes, I measure this correctly at logic board pin ES and see the expected
effect in Z axis amplifire output as described above.

-

I tried to probe the grid-cathode voltage yesterday with my homebrew
"HV" "probe", but it's just to bulky and doesn't stay in place. I
suspect at this point that one of the original caps in the DC restorer
was failed, either open or leaky, and that one of the replacement caps
has the same or a similar problem. I'll buy another round of HV caps and
see if that changes anything.

Cheers,
Marian

Re: 466 +15 supply and U1724 (1458)

Andreas Ragner
 

Please check the health of C1757 (10 mfd) at the +15V rail.

I remember having intermittent problems with my 466 3 years ago - at first the scope did shut down after half an hour of operation, later this tantalum did blow (horrible smell).

Due to lack of tantalum caps I replaced with an electrolytic - still running fine.

Re: 7603 weirdo inverted Z axis

Albert Otten
 

Hi David,

Sorry, it was not my intention to force you to do "homework" calculations!
Having read the discussion again and again, I think I see now why we seemingly disagree about the effect of an open -15V end. You wrote "The intensity control range would also be affected but this might not be
very noticeable if the grid bias was adjusted." and now you wrote "working from 200uA to 75uA if
the grid bias is adjusted appropriately." I was thinking of a properly adjusted scope in which the fault occurs at some instant. But what you meant and mean must be a re-adjustment of grid bias *after* the fault occurred.
BTW A 125 uA change would give about 2.2 V change in voltage across R1159 and in grid-kathode voltage. In my experience such a change, just above cut-off, is well visible but not enough to make you think the intensity range is normal.

Albert

Re: Off topic Hitachi v-152B help?

VK4AU
 

Thanks for the advice. Unfortunately the components in question are in the most in accessible spot, between the Volt/Div switch and PCB and jammed in under the CRT. I had to think about disassembling the whole thing for a while before I dared do it! C26 is fine?, I took it out and it reads 11.5uF (nominally 10uF) and ESR admittedly an a cheapo ESR meter of 0.04. TR3 base however reads -6.8V compared to ground. I have not as yet found a data sheet for TR2 E412S-A. I would appreciate any advice.
Thanks
Mark

Re: 466 +15 supply and U1724 (1458)

 

On 23 Jan 2016 18:04:53 -0800, you wrote:

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.
Are you sure about this? What about the +140 and +65 volt outputs?

The +65 volt output is used as a reference for the other supply
voltages so if it is low, then they will be low also?

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.
Vcc for U1724 being at +4.5 volts is an immediate problem and nothing
around U1724A and U1724B is going to work correctly.

What is the voltage at the +65 volt output?

Is it possible that the 10uf cap to ground at the + input is bad pulling that input down?
I am confused here. The schematic shows C1725 0.02uF at the + input
of U1724A and a C1757 10uF at the +15 volt regulated output.

How does that relate to the low Vcc?
Vcc comes from the +65 volt output so either the +65 volt output is
low making Vcc low or something is wrong with either R1727, VR1725, or
U1724. The connection to Vcc through any socket might be open. See
below.

Thanks. Obviously I'm jet learning op amps.

John
Is U1724 installed in a socket? If so those sockets were known to be
a problem and it may have a bad connection.

You said the output of U1725 is +5.1 volts while Vcc is +4.5 volts. I
am thinking that perhaps Vcc of U1724 is open at the socket and Vcc is
being powered by the output pin which is being pulled up by the +173
volt supply through R1722. That might not explain both inputs of
U1724A being +4.5 volts though.

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
"gate" jack? Let us have some more info.


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