The Z axis amplifier is kinda an op amp in the sense that it is a global feedback amplifier. It does work correctly, both with manually provided inputs and when connected to the Z axis logic.

The intensity pot isn't hooked up backwards.

In the mean time I also checked whether all connections between the tube socket and the pin header in the HV unit are correct, but, unfortunately, they all are correct.

Another possibility is that someone inadvertently changed the circuit during
troubleshooting.

This seems most likely at this point, however there are very few spots in the scope that have been reworked before. Some are on the HV unit (the transformer and the thick film network where exchanged or reworked), but not in that area. I also can't see any changes in parts, except that some European parts have been used in non-critical parts of the circuit (e.g. BZX series Zeners instead of whatever Tek Beaverton specified, I guess this is normal for a Heerenveen-built scope).

I should try to probe the grid and cathode voltages again and see if this is really an issue with the HV unit. Maybe it works correctly after all and there is some strange fault in the tube itself? --- I'd prefer a fault in the HV unit, though.

Those are the same manual I already have, John. I've been told there is a much larger Tek manual for troubleshooting/repair down to component level for the 555. If it does exist that's the one I'm looking for.


Garrett

Hi Ed,
Understod. Anyway, the LCDs I use is about $75 and I get 'em from China (Ebay). It takes a bit of shlocking, but the price is right.

Jay

One more thing - another failure type can happen with certain opamps, where output phase reversal occurs if an input is driven beyond its normal dynamic range. I don't recall how the intensity signals are processed in the 7K scopes, but if opamps are involved, check for proper operating conditions on all pins.


Ed

Unless the pot is hooked up backwards, the only way I can see that a signal can be improperly inverted is in an inverting gain stage that is damaged so that the input signal passes right through without inversion. This can happen in a common-emitter or opamp stage, where a failure or a missing part allows the signal to pass through the feedback loop rather than the active device.


Another possibility is that someone inadvertently changed the circuit during troubleshooting.


Ed

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

Thanks guys, for help with printers. I have several models of Brother laser printers - these are my favorites - I've standardized on them years ago after much disappointment with ink jets and the big brands. The problem with newer printers is that the Centronix port has pretty much disappeared in favor of Ethernet and wireless. I'll have to look at all of them and see what they have for ports and compatibility. I don't want to buy a printer just to go with the scopes - I was hoping to take one out of retirement/spare status and have it work, but maybe it just won't happen.


Ed

Thanks Jay,
It's good to know these are available, but I'd be reluctant to get a new HVPS since the CRT isn't too good anyway. I can't look at it anymore now, but I recall that when it went through all the weird patterns at POST, there was one that lit the whole screen, and it clearly has some phosphor burn of various lines where the traces sat for long times.


I'd be more inclined to go with an LCD panel upgrade, but it probably isn't worth it on this scope. On the 754A it probably would be, if its display craps out.


Ed

There appear to be a few on eBay. Most are listed as service manuals even though they say "instruction manual" on the front. However, looking at listing pictures item 271658505408 looks like the same version that's available on the Tek wiki site that has full diagrams, parts lists, and theory of operation. $26 and free shipping seems reasonable.

John
To: TekScopes@yahoogroups.com
From: TekScopes@yahoogroups.com
Date: Fri, 22 Jan 2016 08:25:33 -0800
Subject: [TekScopes] Tek 555 service manual.


























Was wondering if anyone here had a factory service manual for a 555 scope. I have the instruction manual already. Thanks for any time and help.








Garrett










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

Garrett

IF the manual you have has a part number on the title page in the lower
left hand corner which is 070-165
Then that is the factory Service manual ( actually it is a combined
Operator & service manual ) IF your INSTRUCTION copy has the part number
above on it but has no schematics then your copy is incomplete ...

WE have a COMPLETE copy of that manual for download but I think it is
likely there are free copies available on the WEB


Dave
ArtekManuals.com




On 1/22/2016 11:25 AM, lbfulton@windstream.net [TekScopes] wrote:

Was wondering if anyone here had a factory service manual for a 555
scope. I have the instruction manual already. Thanks for any time and
help.


Garrett



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

Garre

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

Was wondering if anyone here had a factory service manual for a 555 scope. I have the instruction manual already. Thanks for any time and help.


Garrett

I don't know if this helps at all, but the 2040 is a PCL-5e printer.

Vince.

--
Michigan VHF Corp. http://www.nobucks.net/ http://www.CDupe.com/
http://www.foggymist.com The Foggy Mist Emporium

My TDS784D does this as well. I recapped the CRT driver board, which
alleviated this for a spell. I was in email contact with another TDS owner
who found that in his case it was due to degradation of the connections to
the horizontal deflection coil. Apparently there's reasonable peak currents
there and the connector is not so hot.
Once I get through the pile of HP gear hogging my bench ATM, I'll give the
connections a look-see and a good clean, as this random, flickering
shearing is a little annoying.

On Thu, Jan 21, 2016 at 23:04 edbreya@yahoo.com [TekScopes] <
TekScopes@yahoogroups.com> wrote:

Now I'm getting paranoid - I just remembered that lately the 754A display
sometimes has slight flickering in the display shortly after power-up, and
then would be OK after warming up a bit. I hope this is not a sign of
impending doom like a flaw in the HV transformer that gets worse as
happened in the 544A. I'm thinking about maybe opening it up to see if
there's any evidence of HV leakage on the outside of the transformer.



Ed

Hi Ed,

I have a number of those HV assemblies lying around from doing conversions to LCDs
They were converted as the CRTs were too dim for resale. I've been slowly unloading them on Ebay, but they're not hot sellers by any means. You can see one of them in Ebay item 321799417496
http://www.ebay.com/itm/Tektronix-TDS784C-HV-CRT-board-for-TDS700-600-and-500-series-oscilloscopes-/321799417496?ssPageName=STRK:MESE:IT http://www.ebay.com/itm/Tektronix-TDS784C-HV-CRT-board-for-TDS700-600-and-500-series-oscilloscopes-/321799417496?ssPageName=STRK:MESE:IT
If you're in the US, I'll send one to you for $75 including shipping.

Jay

It can never hurt to open it up and have a look.
Except in those cases where you damage something in the process of course. ;-)

Even if there is nothing to be found at the very least it will give
you some idea what to expect when things do go wrong.

ST


On Fri, Jan 22, 2016 at 5:04 AM, edbreya@yahoo.com [TekScopes]
<TekScopes@yahoogroups.com> wrote:

Now I'm getting paranoid - I just remembered that lately the 754A display sometimes has slight flickering in the display shortly after power-up, and then would be OK after warming up a bit. I hope this is not a sign of impending doom like a flaw in the HV transformer that gets worse as happened in the 544A. I'm thinking about maybe opening it up to see if there's any evidence of HV leakage on the outside of the transformer.


Ed



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



------------------------------------
Posted by: edbreya@yahoo.com
------------------------------------


------------------------------------

Yahoo Groups Links

On Thu, 21 Jan 2016, edbreya@yahoo.com [TekScopes] wrote:

I tried the laserjet and almost every other one too, but it didn't work with the Brother HL-2040. I'm wondering if maybe the printer's communication and format settings can be changed via a PC hooked up to it. I don't recall ever seeing any explicit provision for that in printers, since the drivers usually take care of all the details.

According to the user manual, it looks like the HL-2040 only supports GDI. The 2070N supports PCL, Epson FX-850 and IBM Proprinter XL emulation. See pages 2-1, 2-17, A-2 and A-3

https://www.brother-usa.com/ModelDocuments/Consumer/Users%20Manual/UM_HL_2040_2070N_EN_1289.PDF

On Thu, 21 Jan 2016, edbreya@yahoo.com [TekScopes] wrote:

I tried the laserjet and almost every other one too, but it didn't work with the Brother HL-2040. I'm wondering if maybe the printer's communication and format settings can be changed via a PC hooked up to it. I don't recall ever seeing any explicit provision for that in printers, since the drivers usually take care of all the details.

I'm not sure if this will help, but I have a HL-2070N which is the same basic printer as the HL-2040 but it also has a network interface. The default mode for the 2070N is the Epson FX-850 but it can be switched to the IBM Proprinter XL via its built-in webserver based configuration page.

If you happen to need it sometime, I have the service manual for these printers in pdf format. I don't remember where I got it from but Brother doesn't seem to make it publicly available.

Also, if you ever begin to have trouble with the printer not feeding paper, pick up a LM6291001 paper feeding kit (mine was ~$15 from a printer supply company). The feed roller assembly in these printers seems to last for about 20k-25k pages after which the textured roller surface is worn too much to reliably pull paper from the paper tray. Installing the roller requires quite a bit of disassembly (and you have to carefully align the marks on the gears while installing it), but following the diagrams in the service manual makes it pretty easy.

If you have trouble with double-feeds, there is a small rubber dampening pad for the feed solenoid that breaks down and turns into a sticky tar-like goo. Removing it solves the problem, although after removing it, you can definitely hear an audible click when the solenoid pulls in.

Thanks Al,


I tried the laserjet and almost every other one too, but it didn't work with the Brother HL-2040. I'm wondering if maybe the printer's communication and format settings can be changed via a PC hooked up to it. I don't recall ever seeing any explicit provision for that in printers, since the drivers usually take care of all the details.


Ed

Now I'm getting paranoid - I just remembered that lately the 754A display sometimes has slight flickering in the display shortly after power-up, and then would be OK after warming up a bit. I hope this is not a sign of impending doom like a flaw in the HV transformer that gets worse as happened in the 544A. I'm thinking about maybe opening it up to see if there's any evidence of HV leakage on the outside of the transformer.


Ed

Ed:

I have a TDS 544A and it has a centronics parallel port. I have used it with several printers that use the standard HP PCL language. Set the printer options to output to the centronics port and select the laserjet format.

It should work. The PCL format uses ASCII characters and it a very common standard in the older, more expensive printers, from many vendors. Many current printers also support PCL but you have to check the specifications. Very inexpensive printers now do most of the formatting in the PC and require proprietary drivers.

I hope this information helps. I am assuming the your TDS 754A has similar options.

In my TDS 544A there is also a floppy disk that you can use to save standard image formats. These formats can be processed by most PC drawing and word processing programs. That is another way to get a screen print into a document or print it out.

Al Jamison