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troubleshooting Tek453 Mod 210H

chuck
 

Folks,
just bought a 453 and of course there are problems. The trace is fat! Using the 1Khz internal signal when I put it on either channel the trace is out of focus and really hi intensity. The focus knob works to an extent but the intensity knob does nothing. I traced the signal thru the z amp and it behaves as it should as I adjust the knob the signal at the output stage (prior to going into the CRT control circuit) changes. I'm intimidated by the CRT circuitry and would love to get some feedback so that I'm not going in blind. The Tek troubleshooting guide talks about Typical High Voltage problems but does not really point me in a direction.
Any help would be appreciated. I have a couple of DVM's and a pocket scope (Chinese knock off) to work with.
Chuck

Jeff Pederson
 

Probably obvious, but have you checked the trace find circuit, if that is an older one with tubes I have one for parts if interested.

On Wednesday, October 10, 2018, 2:38:26 AM PDT, chuck <@chuckyorbalinda> wrote:

Folks,
just bought a 453 and of course there are problems. The trace is fat! Using the 1Khz internal signal when I put it on either channel the trace is out of focus and really hi intensity. The focus knob works to an extent but the intensity knob does nothing.  I traced the signal thru the z amp and it behaves as it should as I adjust the knob the signal at the output stage (prior to going into the CRT control circuit) changes. I'm intimidated by the CRT circuitry and would love to get some feedback so that I'm not going in blind. The Tek troubleshooting guide talks about Typical High Voltage problems but does not really point me in a direction.
Any help would be appreciated. I have a couple of DVM's and a pocket scope (Chinese knock off) to work with.
Chuck

Kevin Clark
 

On the 22xx series of scopes this fault is related to the focus string resistors gone bad. Something similar maybe ?

Kevin


On 10 October 2018 at 11:11 "Jeff Pederson via Groups.Io" <jpederson32=yahoo.com@groups.io> wrote:

Probably obvious, but have you checked the trace find circuit, if that is an older one with tubes I have one for parts if interested.

On Wednesday, October 10, 2018, 2:38:26 AM PDT, chuck <@chuckyorbalinda> wrote:

Folks,
just bought a 453 and of course there are problems. The trace is fat! Using the 1Khz internal signal when I put it on either channel the trace is out of focus and really hi intensity. The focus knob works to an extent but the intensity knob does nothing. I traced the signal thru the z amp and it behaves as it should as I adjust the knob the signal at the output stage (prior to going into the CRT control circuit) changes. I'm intimidated by the CRT circuitry and would love to get some feedback so that I'm not going in blind. The Tek troubleshooting guide talks about Typical High Voltage problems but does not really point me in a direction.
Any help would be appreciated. I have a couple of DVM's and a pocket scope (Chinese knock off) to work with.
Chuck


Fabio Trevisan
 

Hello Chuck,

When it comes to intensity control inoperative, and highly intense trace, I`m afraid that you're going to set your fears aside about the CRT circuit and playing around it (with all its indeed intimidating High Voltages)...
Still, a lot of those circuits can be troubleshoot on the "Low" side, and what can't, can be troubleshoot by rising one lead of the components and measuring them (with scope turned off).
The regular caution is advised though... To keep one hand in the pocket, to remember to discharge the H.V. points before poking around and, preferably, don't be isolated in the bunker with nobody around.

About the focus, I think you probably don't have a problem in that dept. The trace is fat and the focus can't tame it because it's too intense and the beam is "bloomed".

An inoperative intensity control can have many causes, from a short between grid (G1) and Cathode (K) of the CRT tube, to problems (mostly leakage currents) in the DC restorer circuitry, to defects around the CRT bias circuitry, which encompasses the Intensity control pot and the CRT bias control (usually a trimpot).

All that I`m saying above is general to CRTs and not exactly specific to the 453.

In order to get more specific, anyone in the group will ask you 2 things:
1. If you have a manual, whether in Paper or PDF form (which for the 453 vintage is simultaneously a user and service manual). Some options to download here:
http://w140.com/tekwiki/wiki/453
2. What is the serial number? And if it's really a plain 453, or if it's a 453A.

Please let us know... and we take from there.

Kindest Rgrds,

Fabio

On Wednesday, October 10, 2018, 2:38:26 AM PDT, chuck
<@chuckyorbalinda> wrote:

Folks,
just bought a 453 and of course there are problems. The trace is fat!
Using the 1Khz internal signal when I put it on either channel the trace is
out of focus and really hi intensity. The focus knob works to an extent but
the intensity knob does nothing. I traced the signal thru the z amp and it
behaves as it should as I adjust the knob the signal at the output stage
(prior to going into the CRT control circuit) changes. I'm intimidated by the
CRT circuitry and would love to get some feedback so that I'm not going in
blind. The Tek troubleshooting guide talks about Typical High Voltage problems
but does not really point me in a direction.
Any help would be appreciated. I have a couple of DVM's and a pocket
scope (Chinese knock off) to work with.
Chuck


chuck
 

Fabio,
First thank you for your very specific help. I know what I'm doing today now. LOL Anyway yes I have the service manuals (pdf) howver I think I have the A version and need the non A I can find that on the web.
Second serial number is 005652 so I guess this monster is pre A.

chuck
 

Fabio,
Just thought of something.
So far I have yet to see a tube. Have only lifted the Z amp so far but everything is Xstrs.

chuck
 

Kevin,
Thanks for your tip. Will check these out once I get the courage to get into the CRT circuit. LOL

Brendan
 

On Wed, Oct 10, 2018 at 08:55 AM, chuck wrote:

just bought a 453 and of course there are problems. The trace is fat! Using the 1Khz internal signal when I put it on either channel the trace is out of focus and really hi intensity. The focus knob works to an extent but the intensity knob does nothing.

Fabio,
Just thought of something.
So far I have yet to see a tube. Have only lifted the Z amp so far but
everything is Xstrs.
There will be two rectifier tubes inside the HV box unless someone has made mods, and if you have a below 20,000 serial # the other "tubes" will be nuvistors. The A version has a larger screen than the non-A version. I have 2 non-A 453s one nuvistor and the other is all transistor minus rectifier tubes, both have a screen size of 3 1/2 inches wide by 2 1/4 tall.

Dale H. Cook
 

At 11:53 AM 10/10/2018, chuck wrote:

Second serial number is 005652 so I guess this monster is pre A.
Do you have Nuvistors in the front end and on the trigger board? If so you need the early 453 manual (serials below 20,000). It is at TekWiki:

http://w140.com/mmm/tek-453.pdf

Dale H. Cook, GR/HP/Tek Collector, Roanoke/Lynchburg, VA
https://plymouthcolony.net/starcity/radios/index.html

chuck
 

hi folks,
Just confirmed this is a 453 pre A version.
Found D940 was open and when I looked at the two versions of this circuit there is considerable differences.
D940 is the biggest diode I've ever seen so I guess a 1n911 is not going to do the job. I haven't had a chance to look at the BOM but if any one knows the commercial P/N would be appreciated. Also stray thought what blew the diode? Everything else in the grid bias ckt seems to be alive and well. Any thoughts?
Thanks for your help been a great learning experience for me.
Chuck

Fabio Trevisan
 

Hello Chuck,

On your finding of D940 opened, there is a screaming question... How did you tested it open?
H.V. diodes usually have a very large forward voltage drop (circa 20 volts), and they won't test right on a regular diode test.
Still, assuming your diagnostic is correct and D940 is indeed open, it's a Tek part number 152-0192-00, and the commercial part number is manufacturer specific, it's a VARO 7701-5X.
You can find its specs here:
http://w140.com/Tektronix_Xref_sm.pdf, page 12-2, line 8.
It's a 5kV diode, 50mA rated average forward current. and it has 15V forward voltage drop at the rated current.

Back in 2016, When I needed to diagnose a H.V. problem on my former 464, one of my first suspects were the H.V. diodes, and they're of this same vintage (not the same specs, but are also from VARO).
Back then, I sourced from a local electronics store, a few modern ESJA53-12. They are 12kV, low recovery time H.V. diodes, for currents up to 5mA and they worked fine on the 464, but the original parts on the 464 were 12kV 5mA (so the ESJA53-12 were a perfect match).

The ones on the 453, however, are 50mA, so I guess you will need to source different ones:
Either original parts (new old stock), and two reputable sources that users from Tekscopes group often resort to are:
Sphere: (http://www.sphere.bc.ca/) or...
QService: (https://www.qservice.tv/)...
(No affiliation though... just a happy customer)
Or you can try these folks here: http://hvstuff.com/
Never dealt with them, but they're almost the only source you can find on the net for H.V. oriented stuff.

Krgrds,

Fabio

On Wed, Oct 10, 2018 at 05:16 PM, chuck wrote:


hi folks,
Just confirmed this is a 453 pre A version.
Found D940 was open and when I looked at the two versions of this circuit
there is considerable differences.
D940 is the biggest diode I've ever seen so I guess a 1n911 is not going to do
the job. I haven't had a chance to look at the BOM but if any one knows the
commercial P/N would be appreciated. Also stray thought what blew the diode?
Everything else in the grid bias ckt seems to be alive and well. Any thoughts?
Thanks for your help been a great learning experience for me.
Chuck