TEK 547 no trace


rob@...
 

Hello,
I have a 547 with the following problem;
About 4-5 months ago I switched it on and had a trace (or 2).
After about a minute the trace slowly disappeared from left to right.
The second time after a few days, I switched it on the trace disappeared even faster .
The third time,a few weeks later,whwn I switched it on no trace at all.
The +350V,+225V,+100V and the -150V are all ok.
And so is the -1850V on the cathode.
any suggestions?

Rob


Albert Otten
 

Hello Rob,
This makes me think of the problem with C562 which has been mentioned in several messages, for instance in
https://groups.io/g/TekScopes/message/108397 .
Albert

On Tue, Sep 21, 2021 at 10:00 AM, <rob@audiodynamate.nl> wrote:


Hello,
I have a 547 with the following problem;
About 4-5 months ago I switched it on and had a trace (or 2).
After about a minute the trace slowly disappeared from left to right.
The second time after a few days, I switched it on the trace disappeared even
faster .
The third time,a few weeks later,whwn I switched it on no trace at all.
The +350V,+225V,+100V and the -150V are all ok.
And so is the -1850V on the cathode.
any suggestions?

Rob


Albert Otten
 

Hello Rob,
Now that you mentioned the very early S/N we can forget about the issue with C562.
You might see what the 547 does in XY mode, Horizontal mode in EXT. No input signals needed if you beware of too bright dot (de-focusing makes it safer).
The dot can remain visible now, with position listening to Hor Pos, or can show the same fault as in sweep mode. In either case you narrow down where to search the fault.
Albert


rob@...
 

Hello Albert,
I tried the XY mode,Horizontal mode in EXT.
It takes some time for me getting used to the 547
Still no trace.
Then I tried a 1A4 module I have very recently obtained from Austria. in stead of the 1A1 was in the 547 bay.
Now it works,all 4 channels! I tested it still only for a view minutes.

I now need to whats wrong with the 1A1

I still have a 1A1 I bought from,or was given by Albert Otten around may 2017 !!! I checked my email !!. What a coincidence.
I am not sure if I changed the 1A1's around.One has switches on the input BNC's

regards,
Rob


snapdiode
 

You should always check the four position lights over the CRT too.


Albert Otten
 

I tried the XY mode,Horizontal mode in EXT.
It takes some time for me getting used to the 547
Still no trace.
Then I tried a 1A4 module I have very recently obtained from Austria. in
stead of the 1A1 was in the 547 bay.
Now it works,all 4 channels! I tested it still only for a view minutes.
That's an unexpected good find Rob.
I still don't see how a 1A1 fault can cause a trace shift to the right, but perhaps I read your description "After about a minute the trace slowly disappeared from left to right." wrong. You could also mean that the intensity drops from left to right? You checked all LVs and HV were good. There might be an issue with plugin connector pin 15 or with switch S675 (see diagram <1>). or with an open filament in a plugin tube. Those filaments are in series with amplifier tube V1003 and with the Miller runup tube V91(!).
I now need to whats wrong with the 1A1
I still have a 1A1 I bought from,or was given by Albert Otten around may 2017
!!! I checked my email !!. What a coincidence.
I am not sure if I changed the 1A1's around.One has switches on the input
BNC's
Yes, you are right! Your memory is better than mine. The one with the AC-GND-DC switch concentric with the input BNC was an untested scrap unit. The other one a tested nuvistor type with S/N 701433. You wrote that the latter unit passed a short basic test in your 535, so if you still have that unit you could try it in your 547.

Albert


rob@...
 

Hello Albert,

I tried the 1A1 (701433),I switched it on and after about 30 seconds (delay) I saw a (small) flash of light and I immediately switched it off,It happened to quick for met to see if it drew more power before I switched it off..
The next day I tried the 1A4 and it worked fine.. I was not yet brave enough to try the 1A1 again. I found no signs of burning..

About my description of the trace disappearing,yes I meant the intensity of the trace slowly decreased to zero, starting at the left side of the screen.

Switch S675 is on the 547 or on the input module?
V91 is also hard to find for me.

-Another question; I take it that my HT transformer is dipped in beeswax and not epoxy because my 547 is rather old judged by the serila number?
-Are there important updates that should be carried out?
regards and thanks,
Rob


Albert Otten
 

About my description of the trace disappearing,yes I meant the intensity of
the trace slowly decreased to zero, starting at the left side of the screen.
Switch S675 is on the 547 or on the input module?
V91 is also hard to find for me.
Hello Rob,
I misread the switch number, should be S673 diagram <1> which is activated when the plugin is inserted. See last paragraph of circuit description "+ 100-Volt Supply". V91 is the time base B Miller tube, diagram <5>.
But just forget my suggestions about this, I don't see a relation with that fading trace.
-Another question; I take it that my HT transformer is dipped in beeswax and not epoxy because my 547 is rather old judged by the serila number?
I can't tell you. It seems that the same part number 120-308 was maintained. Tekwiki says that it has been epoxy from the start.
-Are there important updates that should be carried out?
To protect the HV oscillator tube V800 <2> the circuit with D803, R8004 and D804 has been added later on.
If you see a bright flash (moving dot) at the CRT when you switch off the 547, you might implement the modification with mentioned C562.

It's a pity that there was a flash with ex-mine 1A1 unit. I have no idea of course what's going on, sorry.
Albert


Morris Odell
 

If you want to check whether you have a lossy HV transformer, put a voltmeter on the screen (pin 6) of the 6AU5 V800. It should start off at about 90 volts from when the relay pulls in and if the voltage gradually rises and the trace disappears then the transformer needs to be replaced or rewound.

Morris