Date   
Re: 7854 display problem

Fred S.
 

Could be a focus problem, high voltage, or still your power supply. I think the digital part should be fine, you can see a blob where the readout is supposed to be.

--
Best regards,

Fred S.

Re: TDS-540 trips GFI

ham789@...
 

I put 30VDC, max I have easily available, between ground and either line or neutral.
Measured 0A current flow with microamp resolution. Unless there's a breakdown
in the cap that happens over 30V, caps seem to be ok.
Two of the caps are easy to get at. The other two are under a bunch of goop that holds
things together. Maybe I should pop the easy two and hit them with the curve tracer
at higher voltage.

There is a 10 ohm inrush current limiting resistor in the line-side.
It's possible that there's an imbalance at turnon sufficient to trip the GFI.
But I wouldn't be the only one seeing it.

I have a third supply from a TDS-540B that doesn't trip the GFI.
I don't have a schematic for that one, but the input circuit is quit a bit different.

Re: TDS-540 trips GFI

Ken Winterling
 

I guessing these are ceramic disc caps with maybe a 1KV or 1.6KV rating?
They really should be replaced with X, Y, or X/Y mains-rated caps. Ceramic
discs are not designed for continuous AC mains duty.

The caps form a capacitive voltage divider so there is about 60V (for
120VAC mains) to ground. All need to be tested with AC.

You say two of the caps are difficult to access. Is it possible to bypass
the mains filter caps entirely? That would tell you if the filter caps are
the culprit.

Ken
WA2LBI

On Wed, Jan 30, 2019 at 16:59 <ham789@...> wrote:

I put 30VDC, max I have easily available, between ground and either line
or neutral.
Measured 0A current flow with microamp resolution. Unless there's a
breakdown
in the cap that happens over 30V, caps seem to be ok.
Two of the caps are easy to get at. The other two are under a bunch of
goop that holds
things together. Maybe I should pop the easy two and hit them with the
curve tracer
at higher voltage.

There is a 10 ohm inrush current limiting resistor in the line-side.
It's possible that there's an imbalance at turnon sufficient to trip the
GFI.
But I wouldn't be the only one seeing it.

I have a third supply from a TDS-540B that doesn't trip the GFI.
I don't have a schematic for that one, but the input circuit is quit a bit
different.



--
Ken
WA2LBI

Sent from one of my mobile devices

Re: TDS-540 trips GFI

george edmonds
 

Hi
You must make the apparent leakage measurements with AC NOT DC as the filter elements are capacitors.
George G6HIG

On Wednesday, January 30, 2019 9:59 PM, "ham789@..." <ham789@...> wrote:


I put 30VDC, max I have easily available, between ground and either line or neutral.
Measured 0A current flow with microamp resolution.  Unless there's a breakdown
in the cap that happens over 30V, caps seem to be ok.
Two of the caps are easy to get at.  The other two are under a bunch of goop that holds
things together.  Maybe I should pop the easy two and hit them with the curve tracer
at higher voltage.

There is a 10 ohm inrush current limiting resistor in the line-side.
It's possible that there's an imbalance at turnon sufficient to trip the GFI.
But  I wouldn't be the only one seeing it.

I have a third supply from a TDS-540B that doesn't trip the GFI.
I don't have a schematic for that one, but the input circuit is quit a bit different.

Re: TDS-540 trips GFI

ham789@...
 

On Wed, Jan 30, 2019 at 03:11 PM, george edmonds wrote:


Hi
You must make the apparent leakage measurements with AC NOT DC as the filter
elements are capacitors.
George G6HIG
OK, hear me out...
If the capacitors act like capacitors and have the same measured value...
If the leakage is modeled by a parallel resistor that measures > 20 MOhm
with 30VDC applied...
Why is that not sufficient to suggest that the caps are not the problem?
An AC measurement won't change the reactive or resistive components
unless the cap is breaking down when over 30V is applied.
Maybe the leakage is very temperature dependent, but the GFI trips
instantly.
What am I missing?

I took a quick look at removing the caps. The ground plane is huge
and I'm afraid I'll do more harm than good trying to remove them.

Help! I have too many Probes! Please buy some!

 

HELP! I have too many probes! I need to get rid of these extra ones. If you
can use some of these probes, I would appreciate it if you would contact me
OFF LIST at dennis at ridesoft dot com with the list of probes you want.



You have my personal guarantee that all of them are TESTED and WORKING. I
spent the last 3 days doing this to be sure. Unless otherwise noted they are
clean, cosmetically fine, have no labels, and they include a retractable tip
and a ground. A few are brand new with all accessories. A few are dirty but
they will clean up nicely. 40% are missing the retractable tip and 20% are
missing the ground lead. The two P6012s have labels on their compensation
box.



*NOTES ABOUT THE PROBES CONDITION*

1*: Brand new, all accessories included

2*: No ground lead

3*: No retractable tip

4*: On Screen Readout pin

5*: Needs a little cleaning. No labels.

6*: Dirty. Needs a lot of cleaning. No labels.

7*: These two P6012 probes have a label on them.



I will ship using a Priority Mail 2-DayT Small Flat Rate Box. The box will
hold at least 3 probes and probably 4 probes. The cost to mail the box to
the US or Canada is a fixed $10 regardless of how many probes you buy so it
is to your advantage to buy as many as possible. Overseas shipping will have
to be calculated on a case by case basis. Shipping is from Seattle WA (USA).



TekWiki has manuals for all of these probes so if you want to see what they
look like or you want to learn more about them enter the probe number in the
search field on the upper right at http://w140.com/tekwiki/wiki/Main_Page .



PROBE QTY LENGTH US$ DESCRIPTION AND NOTES ABOUT THE PROBE'S CONDITION

P6006 (1) 12ft $8 General Purpose

P6011 (4) 9ft $12 General Purpose

P6011 (9) 6ft $12 General Purpose, 3*

P6011 (1) 6ft $18 General Purpose, 1*

P6012 (9) 3.5ft $10 Miniature General Purpose, 5*

P6012 (2) 3.5ft $8 Miniature General Purpose, 5*,7*

P6028 (1) 6ft $20 General Purpose, 1*

P6049 (3) 3.5ft $15 Miniaturized, For Sony/Tek 323, 3*

P6052 (1) 6ft $8 1X/10X General Purpose, 2*,3*

P6053 (3) 6ft $12 Miniature Fast Rise for 7K Plugins, 2*,3*,5*

P6053 (1) 3.5ft $12 Miniature Fast Rise for 7K Plugins, 2*,3*,5*

P6054 (3) 6ft $8 Miniature Fast Rise, 2*,3*,5*

P6054 (1) 3.5ft $8 Miniature Fast Rise, 2*,3*,5*

P6055 (2) 3.5ft $40 Miniature Differential probe PAIR, 4*

P6061 (2) 3.5ft $10 Miniature for 432, 435, 5000 series, 2*,3*,5*

P6061 (1) 9ft $8 Miniature for 432, 435, 5000 series, 2*,3*,6*

P6061 (1) 9ft $10 Miniature for 432, 435, 5000 series, 2*,3*,5*

P6065 (1) 6ft $15 Miniature For 465 oscilloscope, 4*,6*

P6075A (1) 6ft $15 Miniature For 475 oscilloscope, 3*,4*,5*

P6075A (1) 6ft $15 Miniature For 475 oscilloscope, 3*,4*,6*

P6103B (1) 6ft $15 Modular for 2201/5, 2212/14, 2225, TAS220/250

P6119 (9) 2M $22 Miniature Modular, 1X/10X for 2200 series

P6119B (6) 2M $25 Miniature Modular, 1X/10X for 2200 series

P6131 (3) 1.3M $30 Subminiature, for 2465/2445/7A42, 3*,4*

P6131 (4) 1.3M $100 Subminiature, for 2465/2445/7A42, SET OF 4, 3*,4*



Dennis Tillman W7PF

7A18 plugin innards for cost of shipping

Thomas Garson
 

Tried to post this as a reply to another message. Seems like it went into the cloud and never came out.....

I have the innards of a 7A18 plugin available for the cost of shipping.

I gutted the 7A18, which I purchased DOA with knobs already removed, for use as a platform to build John Greissens 7000 Plugin Extender, which works dandy, by the way.

No idea if these parts are any good, but switches, pots, board, etc. all looked undamaged.

Reply to me if interested. Figure shipping in box big enough to hold 2 7000 plugins (don't know exact size/weight) from Ashland, Oregon 97520.

7A18N plugin guts: Free with shipping

Thomas Garson
 

I recently gutted a dead (bought DOA with knobs already missing) 7A18N single trace 7000 plugin to use as a platform/chasis for a John Griessen Plugin Extender kit.

Before I toss all of the 7A18N interior parts, I'm offering them to anyone who wants them free if you pay the shipping. Origin zip: USA 97520.

First come, first serve.

Please reply to tgarson@... if interested.

Tom Garson


PS:

Building the extender took  more than a bit of effort but was worth it. Johns boards are excellent.

Re: No start 7854 Power supply

Doug Bercich
 

Congratulations, David!! Thank you for sticking with this rather frustrating repair and sharing all the details with the group. As a fellow 7854 owner I hope I never actually need this information but it’s very good to know, just in case; I’m certainly more familiar with the inner workings of this PSU now. Best regards!


________________________________
From: tekscopes@groups.io on behalf of David C. Partridge <@perdrix>
Sent: Wednesday, January 30, 2019 6:26 AM
To: tekscopes@groups.io
Subject: Re: [TekScopes] No start 7854 Power supply

SOLVED !!!

OK, The voltage at the emitter of Q45 was about 110V, which was less than the voltage at the base (118V) which is set by the Zener diode VR45, so the over-voltage circuit wasn't causing the shutdown.

Not long afterwards the supply changed its behaviour, settling down in to what I can best describe as "normal" tick-mode.

I then spent a few happy hours chasing my tail, looking at the I-Sense (pin 13) and E-Sense (pin 15) signals on the controller IC to see if they were causing the oscillator stop signal on pin 8 to be asserted.

I should say at this point that I was using a dummy load connected to P82 on the LV regulator board.

I checked the schematic just before probing the Fault-Sense signal at pin 2 and realised that without the thermal switch connected to the LV board that a supplies out of balance condition would shut the inverter down.

Once I put a jumper on P72 on the LV regulator, the supply sprang to life!

In summary there were multiple faults on this supply and one pilot error :)

1. Both inverter transistors were dead short.

2. R44 in the over-voltage stop circuit had literally broken in two.

3. Both CR36 and CR37 in the inverter control circuit had leads corroded through.

4. Lots of under board corrosion, solder in some holes corroded away.

5. The 22 ohm inverter base drive resistors (R32 and R40) were both open circuit (even though they looked OK).

6. The collector lead of Q46 (over-voltage stop) was corroded away where it connected to the can.

7. Pilot error - PUT A JUMPER ON P72 ON LV BOARD WHEN USING A DUMMY LOAD

The supply was ticking when it was installed in the MF, so on a hunch I checked the thermal cut-out switch by probing the connector that went on P72. That was open circuit, but that turned out to be simple as one of the wires had come off the thermal switch.

The mainframe now powers on but there are other issues - but that's for another thread.

Dave

Re: TDS-540 trips GFI (maybe it's not the capacitors)

Brad Thompson
 

ham789@... wrote on 1/30/2019 4:59 PM:

<snip>
Two of the caps are easy to get at. The other two are under a bunch of goop that holds
things together.
<snip>

It's possible that with the passage of time, the "goop" has become conductive and
is providing a leakage path across the capacitors. I ran into this several years ago
(at the time, melamine was showing up in Chinese-processed milk):

https://cdr.cz/sites/default/files/Bad_glue.pdf

<https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=2ahUKEwiKyd7185bgAhWJdt8KHTFMCS4QFjACegQIAxAC&url=https%3A%2F%2Fcdr.cz%2Fsites%2Fdefault%2Ffiles%2FBad_glue.pdf&usg=AOvVaw0WqqJkz2wrOUZQf9uuXkiy>
If the glue is present, carefully scrape it away from the capacitors and
note whether any "tracking" is visible on the PC board beneath the capacitors.

73--

Brad  AA1IP

Please let me post messages to the group

Art
 

--

Thanks,
Art

Where To Find Tek 2246 Spare Parts

Art
 

Spent the last 2 days tracking down why the scope does not display a trace
with the service manual and schematics. Beam Finder does show 4 dots one
for each channel and vertical position adjustment works. The on-screen text
appears and changes when the controls are changed so the general CRT
functions ok. Power supply voltages are in spec and clean.

Fairly sure U421 A Trigger Source Selector IC is defective (Tektronix Part
# 234023920). Timing signals arrive and no output while U431 B Trigger
Source Selector which receives most of the same inputs as U421 outputs the
expected trigger signals.

I emailed a request for the cost of the part from Tektronix. Couldn't find
the part on eBay just broken units which could be scavenged. QService
Electronics lists the part out of stock.

Any other suggestions.

Re: TDS-540 trips GFI

george edmonds
 

Hi    
It is simple, if the input filter is of standard design you, effectively in its simplest form, have two capacitors one from the phase (live) and one from the neutral.  Both go to ground, the phase to ground has incoming supply across and a current flowing through it (reactive component) whereas the neutral to ground has no voltage across it, and no current flowing through it. This produces an unbalanced AC current between live to ground and neutral to ground which trips the GFI (RCD for those that speak real English).
At DC this problem will not show.
George G6HIG

On Thursday, January 31, 2019 12:28 AM, "ham789@..." <ham789@...> wrote:


On Wed, Jan 30, 2019 at 03:11 PM, george edmonds wrote:


Hi
You must make the apparent leakage measurements with AC NOT DC as the filter
elements are capacitors.
George G6HIG
OK, hear me out...
If the capacitors act like capacitors and have the same measured value...
If the leakage is modeled by a parallel resistor that measures > 20 MOhm
with 30VDC applied...
Why is that not sufficient to suggest that the caps are not the problem?
An AC measurement won't change the reactive or resistive components
unless the cap is breaking down when over 30V is applied.
Maybe the leakage is very temperature dependent, but the GFI trips
instantly.
What am I missing?

I took a quick look at removing the caps.  The ground plane is huge
and I'm afraid I'll do more harm than good trying to remove them.

Re: Help! I have too many Probes! Please buy some!

 

Hi Dennis I could use a couple suitable for my Rigol 1102D.
U have anything for that scope?

Re: Where To Find Tek 2246 Spare Parts

qservice@...
 

The Part 234-0239-20 is available ( ex-equipment ) only by request from qservice, have already said that in a direct email

thanks Dinos

Re: 7854 display problem

 

OK I just ran through the Z-Axis calibration and pretty much everything
looked just fine on the test scope.

The following test was done with readout on the 7854 turned off.

Looking at the waveform at TP183 on the Z-Axis board: With the 7854
intensity set to minimum, the base line is at about 9.5V, and while a sweep
is running the voltage is about 20V. If I increase the intensity to
maximum, the voltage is about 80V, which is correct. The signal has a
flat top (no variation), and the variation in the peak voltage is linear
with the intensity control.

With the intensity set to minimum there is no obvious trace, but there are
very short bright dots at fairly random locations along the line where the
trace would be. As I increase the intensity to the 270 degree position
(dot on knob pointing to left) the dots disappear but no trace appears.
Nothing is then visible until the intensity control reaches just before the
90 degree position (dot on knob to right). At this point a somewhat out of
focus trace with intensity modulation along its length appears, and finally
with intensity to maximum the trace is a bit more out of focus and somewhat
brighter but still modulated. The modulation appears to about 1-2 cycles
per sweep division when the timebase in the 7854 is set to 10mS/div.

At this stage I'm guessing it's probably some sort of problem in the HV
circuitry (possibly the cathode supply) or maybe the DC restorer, or even
the EHT supply to the anode? I suppose it might also be a dying CRT?

I have scoped the cathode supply using a P6015 and it's close to -3kV with a
square wave ripple of about 0.5Vpp at 25.5kHz.

Your thoughts most welcome ...

David

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of David C.
Partridge
Sent: 30 January 2019 18:30
To: TekScopes@groups.io
Subject: Re: [TekScopes] 7854 display problem

Drat it - it still split the link!

<https://tinyurl.com/ycarxp3k>

David
-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of David C.
Partridge
Sent: 30 January 2019 15:43
To: TekScopes
Subject: [TekScopes] 7854 display problem

OK when I powered this 7854 on fixing the PSU, if failed POST with a ROM
failure (dratted Mostek mask ROMs).

So as to be able to continue testing, I "borrowed" the ROM board
(670-5047-02) from my personal 7854 and put it in the patient.

It passed POST, but this is what the screen looks like: <
https://groups.io/g/TekScopes/files/7854/7854%20Initial%20Display%20Problem.
MOV>

It sort of looks like it may be trying to display the normal Self Test
Complete screen, but it sure isn't right!

Any suggestions for likely culprits?

Thanks
David

Re: Anyone have a Tek 555 interconnection cable for sale

widgethunter
 

I may have a cable - not thrilled at parting with it but do not want to see a 555 butchered...
Will have to go dig. The connectors are worth crazy money and I have not found a better HV interconnect.
So, this wouldn't be a freebee.

-----Original Message-----
From: Matt Russell <statesomattr@...>
To: TekScopes <TekScopes@groups.io>
Sent: Tue, Jan 29, 2019 6:28 pm
Subject: Re: [TekScopes] Anyone have a Tek 555 interconnection cable for sale

AWESOME! Do you have a cable, or just ends? I live in Orrington, Me 04474 and I will cover costs happily

RM504 power supply simulation

boid_twitty
 

Some time ago I redesigned and rebuilt a power transformer for the regulated supplies in an RM504.

An LTspice simulation is now available using models provided by Nakabayashi. The coincidence that there should be models for both the 6DQ6 and 6BL8 is pretty slim, unless Ayumi was simulating the same circuit at one time or another.

The simulation is available at:

http://ve3ute.ca/query/RM504_power_supply_sim.zip

It should run out of the box - not very fast, but worth the trouble running, if you're interested in this application.

Re: RM504 power supply simulation

David Holland
 

Hmmm, returns a 404 (Not Found)......

??

On Thu, Jan 31, 2019 at 4:59 PM boid_twitty <legg@...> wrote:

Some time ago I redesigned and rebuilt a power transformer for the regulated supplies in an RM504.

An LTspice simulation is now available using models provided by Nakabayashi. The coincidence that there should be models for both the 6DQ6 and 6BL8 is pretty slim, unless Ayumi was simulating the same circuit at one time or another.

The simulation is available at:

http://ve3ute.ca/query/RM504_power_supply_sim.zip

It should run out of the box - not very fast, but worth the trouble running, if you're interested in this application.


New member

John Williams
 

Hi. My name is John. I have just joined so I would like to observe for a bit to get the hang of being on here. My interests are 500 series restoration and repair. My google photo sight is

https://photos.app.goo.gl/vWHUhwHc74o7ed7Q9

I am looking forward to being a member of this group..