Date   

Re: Tektronix 475

Tom Gardner
 

On 12/08/20 15:05, Chuck Harris wrote:
CRT's take rather a lot of negative grid voltage, WRT cathode,
to cut the beam off. Most take from -50 to -100V.

-18V would be full brilliance.
That corresponds with my recollection (and the ~150V uses in the Z axis circuit), but it has been a few years since I looked.

I recall the peak-to-peak voltage being ~100V, but the AC RMS voltage measured with a meter varies widely depending on the timebase, trigger, and holdoff controls.

Looks like your CRT is off the hook!

Invest some time in the circuit descriptions, starting on p3-16.

It's time to fix your bad DC restorer circuit.
Only after the ground referenced Z axis waveform has been shown to be correct.

Then, if the AC RMS component  of the ground-referenced and HT waveforms differ, the  DC restorer is likely faulty.

With my CRT's broken grid they were the same, which encouraged me to extract the CRT and find the fault.


tenareze32@gmail.com wrote:
The maximum grid-cathode voltage I can attain is -18 V which I reckon should cut off the beam, but I don’t have the specification for this tube. The grid bias pot does reduce this voltage at certain settings of intensity as does the intensity control. These adjustments would increase the brightness, but it is already too bright. All the components in the DC restore circuitry test OK and the extra winding on the HT transformer is producing about 40 V p-p (though 47 pF and 390 kΩ), which I assume produces the maximum negative bias for the grid.
I’ll troubleshoot the Y amplifier to see whether it might be worth replacing the tube.
Simon


Re: Tektronix 475

Chuck Harris
 

CRT's take rather a lot of negative grid voltage, WRT cathode,
to cut the beam off. Most take from -50 to -100V.

-18V would be full brilliance.

Looks like your CRT is off the hook!

Invest some time in the circuit descriptions, starting on p3-16.

It's time to fix your bad DC restorer circuit.

-Chuck Harris

tenareze32@gmail.com wrote:

The maximum grid-cathode voltage I can attain is -18 V which I reckon should cut off the beam, but I don’t have the specification for this tube. The grid bias pot does reduce this voltage at certain settings of intensity as does the intensity control. These adjustments would increase the brightness, but it is already too bright. All the components in the DC restore circuitry test OK and the extra winding on the HT transformer is producing about 40 V p-p (though 47 pF and 390 kΩ), which I assume produces the maximum negative bias for the grid.
I’ll troubleshoot the Y amplifier to see whether it might be worth replacing the tube.
Simon




Re: TM500 Plug-in Extention

Stephen
 

On Wed, Aug 12, 2020 at 01:58 AM, Colin Herbert wrote:

Interleaved answers

I am replying to this posting because I can see some errors/misunderstandings
in what you did at this time.

There are good reasons why Tektronix used more than one connector for what
appeared to be the same purpose. It is often the case that high current that
needs to be drawn is shared among a number of connections. It is a mistake to
neglect those multiple connections such as 3A, 3B, 4A and 4B -they are all
designated as "+11.5 V Common Return", and they are current-sharing
connections. It is best to wire them all.
I wired everything from 1A/B to 13A/B with the exception of 6B.

A further possibility is that a
trace going to one of these in the mainframe may have been damaged and no
longer connected. If that is the only connector you have wired up, it won't be
connected to anything.
I’m not sure what you mean exactly, but whichever connector I plug the extender to, or the plugin directly to, yields the same result.

I think you may be having some problem with the "floating" AC supply
connectors; these are not connected to ground or chassis at the mainframe end,
they are floating away from ground. Connectors 1A and 1B are _not_ going to
the same place, but are the two ends of a floating 25 VAC winding on the
transformer. If you just connect one, you will get nothing and if you short
them together, you will just have shorted out a transformer winding.
They are not shorted together. The issue I have is when I “DON’T“ use the extender. “WITH” the extender the plugin works fine.

The same is true of the other 25 VAC winding going to 13A and 13B - connect them both
but don't short them together, thinking they are going to the same point. The
same goes for the 17.5 VAC winding going to 5A and 5B.
Yes, they are neither shorted nor are connected together.

Considering the other contacts that you say you only used one wire for, it is
true that 3A, 3B, 4A and 4B all connect to the same place, but 2A and 2B most
certainly do not go to the same place as those. Connectors 2A and 2B are
designated "+11.5 V Filtered DC" and are going to one place, but not to "+
11.5 V Common Return".
I just followed a tutorial document of which I put a link to in one of the threads...
Here’s a picture of what it says: https://groups.io/g/TekScopes/photo/251875/0?p=Created,,,20,2,0,0

If I were you, I would have yet another look at what you have wired up and
make sure that ALL connections are made, even 6B (No connection) and 10B
(Transformer shield lead). Those may seem redundant, but if you wire
everything up correctly, it leaves less room for errors and does exactly the
same as the Dan Meeks extender and (I assume) the original Tektronix one. It
makes sense.
I agree. 10A/B are connected. Just 6B isn’t.

I did the test you suggested to see the windings were not out of phase. They are not.
Here’s a picture of 5 on top and 13 at the bottom. 1 looks the same. Although not very pretty sine waves. It looks to me that the top is clipping.... This is directly on the mainframe.

https://groups.io/g/TekScopes/photo/251875/1?p=Created,,,20,2,0,0

Colin.
PS: The blood-tests were routine monthly things because I had Deep Vein
Thrombosis ages ago and am on anticoagulant, which needs a bit of monitoring.
Happy all is ok then,


Re: TM500 Plug-in Extention

Colin Herbert
 

I am replying to this posting because I can see some errors/misunderstandings in what you did at this time.

There are good reasons why Tektronix used more than one connector for what appeared to be the same purpose. It is often the case that high current that needs to be drawn is shared among a number of connections. It is a mistake to neglect those multiple connections such as 3A, 3B, 4A and 4B -they are all designated as "+11.5 V Common Return", and they are current-sharing connections. It is best to wire them all. A further possibility is that a trace going to one of these in the mainframe may have been damaged and no longer connected. If that is the only connector you have wired up, it won't be connected to anything.

I think you may be having some problem with the "floating" AC supply connectors; these are not connected to ground or chassis at the mainframe end, they are floating away from ground. Connectors 1A and 1B are _not_ going to the same place, but are the two ends of a floating 25 VAC winding on the transformer. If you just connect one, you will get nothing and if you short them together, you will just have shorted out a transformer winding. The same is true of the other 25 VAC winding going to 13A and 13B - connect them both but don't short them together, thinking they are going to the same point. The same goes for the 17.5 VAC winding going to 5A and 5B.

Considering the other contacts that you say you only used one wire for, it is true that 3A, 3B, 4A and 4B all connect to the same place, but 2A and 2B most certainly do not go to the same place as those. Connectors 2A and 2B are designated "+11.5 V Filtered DC" and are going to one place, but not to "+ 11.5 V Common Return".

If I were you, I would have yet another look at what you have wired up and make sure that ALL connections are made, even 6B (No connection) and 10B (Transformer shield lead). Those may seem redundant, but if you wire everything up correctly, it leaves less room for errors and does exactly the same as the Dan Meeks extender and (I assume) the original Tektronix one. It makes sense.

Colin.
PS: The blood-tests were routine monthly things because I had Deep Vein Thrombosis ages ago and am on anticoagulant, which needs a bit of monitoring.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Stephen
Sent: 10 August 2020 12:56
To: TekScopes@groups.io
Subject: [TekScopes] TM500 Plug-in Extention

I’ve finally found the time to make an extender using JAMMA connectors to be able to troubleshoot my DC 503 and my SC 502

I’ve removed the bridge connections from 1-2 and 3-4, and wired all the pins from 1-5 and 7-13.
Pretty straight forward process. I didn’t connect anything beyond pin 13. Pins 2-3-4-8-12 use only one wire As both sides are connected.

I’ve tried PS503 and it works fine, except that when inside the TM, I can check the +/- 20VDC AND the +5VDC while my ground lead is connected to either ones on the plugin. But not when connected via the extender.

However, no other plugin (AM502, DC503, FG503) is working besides the PS503...
I’ve checked the voltages, and everything is exactly the same on the extender as on the TM506 connector itself.
There’s also full continuity between both ands of the extender.

I understand that pin 14 to 28 are not used when it comes to just power the plugins...

What am I doing wrong??


Re: TM500 plug in extension cables.

Ed (SCSKITS)
 

I agree with Walter, I find that a TM502 core works well for single and double width plug in repair.

ed


Re: Tektronix 475

Simon
 

The maximum grid-cathode voltage I can attain is -18 V which I reckon should cut off the beam, but I don’t have the specification for this tube. The grid bias pot does reduce this voltage at certain settings of intensity as does the intensity control. These adjustments would increase the brightness, but it is already too bright. All the components in the DC restore circuitry test OK and the extra winding on the HT transformer is producing about 40 V p-p (though 47 pF and 390 kΩ), which I assume produces the maximum negative bias for the grid.
I’ll troubleshoot the Y amplifier to see whether it might be worth replacing the tube.
Simon


Re: Tektronix 2230

Saroj Pradhan
 

Hi satbeginner
Yes we did it!
There is an issue with preregulator.
When I turn on the scope it gives me 40v at tp940 and very slowly decreases to 38v which in turn causes to decrease the voltages at low voltage power supply side. May be that is the reason for the issue that I have right now with the scope.
Measuring the voltages across R907 and R949 and doing some calculation I found that
Inverter draws around 1.8A and 1.5A flows Through R907. 1.8A is quite normal as many thread and that preregulator testing document say about that current. But for current through R907 I am not sure.
Thanks
Saroj


Re: TM500 DM511 Digital Multimeter Service Manual?

Colin Herbert
 

Generally speaking, TekWiki is the first place to look for Tektronix
manuals. The DM 511 is there:

http://w140.com/tekwiki/wiki/DM511

What's more, it's free.
If you want top-quality scans and are prepared to pay for them, then Artek
Manuals is probably the best place to go:

http://artekmanuals.com/

I have never bought from them, as I prefer the genuine paper manuals. Other
people sing their praises.
Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Don
Bitters via groups.io
Sent: 12 August 2020 02:35
To: TekScopes@groups.io
Subject: Re: [TekScopes] TM500 DM511 Digital Multimeter Service Manual?

I did a quick search and found op and Serv manual on CD from:
https://www.tennesseequipment.com/East-Cost-/South-Carolina-/Consulting-/Tek
-DM5110-DM511-operating-service-manuals-2-vols.pl
price if any unknown.
Don Bitters


Re: 7834 Missing Trace

Roger Evans
 

Congratulaions on getting the plugin removed, it must be a great sense of relief when it comes out without breaking anything. If the actual edge connector was responsible for much of the stiffness then brush some IPA onto the PCB edge of the plugin and on to the sockets attached to the interface board.

While the 7A12 is out, remove, clean and reseat the two 8pin op-amps U550 and U570. If you have a probe lead you can use the 7A12 to invertigate noise on its own power supplies. Use the Invert setting since it gives a clean signal on the calibrator. You need to probe the two test points labelled TP +/-9V on the schematic and also the resistor/inductor combinations LR556, LR557 etc that provide additional decoupling. It is best to set the two DC levels as best you can before doing the noise probing and also make the DC measurements on U550 and U570. If you need to replace U550 / U570 they are very cheap and easily obtainable. It would do no harm to move R551 back and fore a few times before finally setting it, a dirty sliding contact in R551 could be responsible for the noise.

Hope the good progress continues,

Roger


Re: 5S14N what should I know?

Szabolcs Szigeti
 

Hi,

Thanks, it is good to know that longer wires make such a difference in this
application. Although maybe that could be solved by placing a capacitor
right next to the board. I'll have to experiment with it, although probably
conversion to LEDs would be the best solution.

Szabolcs


Roger Evans via groups.io <very_fuzzy_logic=yahoo.com@groups.io> ezt írta
(időpont: 2020. aug. 11., K, 18:38):

I have a 7S14 which I use infrequently and I am quite happy with 1.5V
watch batteries. I don't think the rise time is greatly affected by the
difference between 1.35V and 1.5V, the sampling diode on time will be
slightly less because of the larger reverse bias but this is taken out by a
small change in loop gain. I did find the wiring of the batteries to be
critical, I wanted to put them in holders but the extra size made the
wiring awkward and the longer leads and extra inductance were a killer. If
you want a quick check that the 5S14 is working, solder two wires to a
standard watch battery and connect it in with short wires, the original Hg
batteries have strip connections which presumably helps to keep the
inductance down.

Have fun,

Roger




Re: TM500 DM511 Digital Multimeter Service Manual?

Don Bitters
 

I did a quick search and found op and Serv manual on CD from:
https://www.tennesseequipment.com/East-Cost-/South-Carolina-/Consulting-/Tek-DM5110-DM511-operating-service-manuals-2-vols.pl
price if any unknown.
Don Bitters


Re: 7834 Missing Trace

sdferg7@...
 

Actually I just found U550 next to U570 now, there's a lot of gunk covering the silk screen label and I didn't spot it when it was in the scope. This plugin is definitely the worst looking part of the scope in terms of internals.

Shane


Re: 7834 Missing Trace

sdferg7@...
 

Huzzah, thanks Colin, I got it out. The thing is, I still had a lot of trouble even with your technique, so I tried it on my left timebase which is also missing the latch, and my right timebase without pulling the tab, and both came out very easily. After I had both sides open around it I managed to get a good grip on the plugin and had to use a lot of force to pull it out. It seems the majority of what was holding it up was the actual connector holding the board contact pins. I can see now that the entire pull tab and plastic strip along with the spring are gone in both the 7A12 and my left timebase.

My original plan was to remove the rest of the latch temporarily once I had them out, but it appears that has already been done. What else can I do to prevent them from getting stuck again?

Before I took it out I measured VR550 and the upper leg measured about -8.9V, the lower leg measured 0V. I checked R551 as well again and it is up to about 8.9V now. I was unable to locate U550, is it perhaps under one of the daughter boards?

Shane


Re: Tektronix 2230

satbeginner
 

Hello Saroj,

about your other message to me:

"Now there is only one issue, the text on the screen disappears to the lower side of the screen after a while.
During two hours of time the nearly half of the text disappeared. I will attach a photo for your reference.
Thanks"

I am not familiar with the specifics of the 2230, but if it works similar to other TekScopes, I presume the readout will be done during flyback of the trace.
The vertical positioning of the readout is usually done by a vertical analog switch-chip or circuit.
In many cases the position of the readout can be adjusted separately, but it also may be necessary to follow (a part of) the calibration routine to adjust that....

I will read the service manual on that part to see if the position of the readout is mentioned separately.

Will contact you later,

well done so far,

Leo


Re: TM500 Plug-in Extention

Stephen
 

On Tue, Aug 11, 2020 at 07:04 AM, Colin Herbert wrote:


No, I don't think so. If you "invert" the connections for 1A-1B and 13A-13B
you will just get the same result; they will still be out-of-phase with one
another. If you just reverse the wiring on either 1A-1B _or_ 13A-13B, you will
have the opposite situation to what you have already - it will work on the
mainframe, but not on the extender. I still think you need to ascertain the
state of the phasing of the three AC windings. It still doesn't solve the
problem of your oddly-behaving home-made extender. That could still be
something associated with the JAMMA parts. I might think of something else
overnight and after I have had some blood-tests done tomorrow morning. But
don't forget, when you have eliminated all of the sensible possibilities, you
are left with the illogical ones that you wouldn't have thought about
otherwise.
Colin.
I see... will do.
And good luck with you blood test!

Thank you


Re: TM500 Plug-in Extention

Colin Herbert
 

No, I don't think so. If you "invert" the connections for 1A-1B and 13A-13B you will just get the same result; they will still be out-of-phase with one another. If you just reverse the wiring on either 1A-1B _or_ 13A-13B, you will have the opposite situation to what you have already - it will work on the mainframe, but not on the extender. I still think you need to ascertain the state of the phasing of the three AC windings. It still doesn't solve the problem of your oddly-behaving home-made extender. That could still be something associated with the JAMMA parts. I might think of something else overnight and after I have had some blood-tests done tomorrow morning. But don't forget, when you have eliminated all of the sensible possibilities, you are left with the illogical ones that you wouldn't have thought about otherwise.
Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Stephen
Sent: 11 August 2020 17:36
To: TekScopes@groups.io
Subject: Re: [TekScopes] TM500 Plug-in Extention

On Tue, Aug 11, 2020 at 05:28 AM, Colin Herbert wrote:


If you disconnect (I assume that's what you mean by "reserve") 1A, 1B, 13A and
13B then you won't get the 25 VAC connections going to your plug-in and I
suspect that it won't work properly, or even at all.
I meant “invert”, sorry. Typo.
I mean putting the wire from 1A, to 1B and vice-versa. Same for pins 13A and B.


Re: 7834 Missing Trace

Colin Herbert
 

I think I have the answer, having tried this with my 7623A with a 7A12 in the left-most bay:

With the bottom off and the scope on its right side, so you have as much access to the leftmost plug-in compartment as you can get, push an ordinary flat-blade screwdriver (having a blade width of about 6mm so that it has a bit of strength in it and won't bend too easily) under the plug-In below where the latch-knob would be. You don't need to wedge it in particularly tightly, just enough so that you can lever the screwdriver enough to wobble the plug-in up and down in its compartment (that is, left and right since the scope is lying on its side). While you do this wiggling, apply some leverage on the solid parts on the plug-in frame to encourage it to emerge from the front of the compartment. Unless there is something else holding it from moving, the plug-in should eventually pop out of the front of the compartment once its latch release bar has allowed it to do so.

When the plug-in is out, don't put it back in that compartment until you have sorted out the release mechanism so that it will work properly in future. Your next job is to find the person who put the plug-in into that leftmost compartment without being able to remove it easily. Find something big and heavy and hammer that numpty into some crevice where he will find it difficult to get out of, either that or ask for a price reduction!
Good Luck with the wiggling!
Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of sdferg7@gmail.com
Sent: 10 August 2020 19:58
To: TekScopes@groups.io
Subject: Re: [TekScopes] 7834 Missing Trace

Here is the bottom of mine: https://imgur.com/a/B0FAYRI

I'm not sure how to get to the spring or plastic without taking the whole bottom frame apart to remove the black guide rails. I can't access them from the side of the plugin either as far as I can tell.

Shane


Re: TM500 Plug-in Extention

Stephen
 

On Tue, Aug 11, 2020 at 05:28 AM, Colin Herbert wrote:

connections 1 and 2 on both sides (i.e. > 1A and 2A connected; 1B and
2B connected) and 3 and 4 on both
sides (i.e. 3A and 4A connected; 3B
and 4B
Yes they are. I removed these connections. Everything else are just point to point connections...

That’s why this is so baffling...


Re: 5S14N what should I know?

Roger Evans
 

I have a 7S14 which I use infrequently and I am quite happy with 1.5V watch batteries. I don't think the rise time is greatly affected by the difference between 1.35V and 1.5V, the sampling diode on time will be slightly less because of the larger reverse bias but this is taken out by a small change in loop gain. I did find the wiring of the batteries to be critical, I wanted to put them in holders but the extra size made the wiring awkward and the longer leads and extra inductance were a killer. If you want a quick check that the 5S14 is working, solder two wires to a standard watch battery and connect it in with short wires, the original Hg batteries have strip connections which presumably helps to keep the inductance down.

Have fun,

Roger


Re: TM500 Plug-in Extention

Stephen
 

On Tue, Aug 11, 2020 at 05:28 AM, Colin Herbert wrote:


If you disconnect (I assume that's what you mean by "reserve") 1A, 1B, 13A and
13B then you won't get the 25 VAC connections going to your plug-in and I
suspect that it won't work properly, or even at all.
I meant “invert”, sorry. Typo.
I mean putting the wire from 1A, to 1B and vice-versa. Same for pins 13A and B.

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