Tek 2235 Good Focus but High Intensity

[DB20Bogen]

I have a Tek 2235; the trace focus is sharp and the focus control exhibits a normal range of control. However the intensity control has no effect (trace is at max. intensity), retrace is dimly visible. The the voltage across 510K resistors (R888 315V, R889 310V, R890 313V R891 309V) in the focus divider are reasonable. All other scope functions are normal. Suggestions??

 

[dorke]

Any effect of horizontal modes A,ALT,B ?
Have you tried operating the Z-axis ?

Do you have another scope to debug the faulty one?

 

[73's de Edd]

.


Sir . . . . . .DB20Bogen . . . . . . (And 'ole Bogen amps don't require this high degree of instrumentation sophistication.)

How about a cold dead set condition and measuring that series string of resistors again as per their resistance readings and ALSO include the one at the very head of the supply on the HV side and the low side of the focus supply as R894 which is being . . . . . guess what . . . yet another 510 K.


Went into my "mule barn" archives and pulled its schematic and then UNITIZED it into one cross page flowing unit, instead of its two pages in the manual.
I think that it will cover all of the situations relevant points of interest, and provide us with a shared reference schematic .


Schematic referencing:

Off site Access as:

http://i.imgur.com/k2xMB8v.png



73's de Edd


.

 

[shrtrnd]

Did you check to see if the intensity control pot itself is bad?

 

[dorke]

.


Sir . . . . . .DB20Bogen . . . . . . (And 'ole Bogen amps don't require this high degree of instrumentation sophistication.)

How about a cold dead set condition and measuring that series string of resistors again as per their resistance readings and ALSO include the one at the very head of the supply on the HV side and the low side of the focus supply as R894 which is being . . . . . guess what . . . yet another 510 K.


Went into my "mule barn" archives and pulled its schematic and then UNITIZED it into one cross page flowing unit, instead of its two pages in the manual.
I think that it will cover all of the situations relevant points of interest, and provide us with a shared reference schematic .


Schematic referencing:

Off site Access as:

http://i.imgur.com/k2xMB8v.png



73's de Edd


.

Ed,
Those resistors are related to focus.
The intensity issue is totally different!
It is at pin number 3 of the CRT.

DB20Bogen,
Please respond to my previous reply ( #2).

 

[DB20Bogen]

.


Sir . . . . . .DB20Bogen . . . . . . (And 'ole Bogen amps don't require this high degree of instrumentation sophistication.)

How about a cold dead set condition and measuring that series string of resistors again as per their resistance readings and ALSO include the one at the very head of the supply on the HV side and the low side of the focus supply as R894 which is being . . . . . guess what . . . yet another 510 K.


Went into my "mule barn" archives and pulled its schematic and then UNITIZED it into one cross page flowing unit, instead of its two pages in the manual.
I think that it will cover all of the situations relevant points of interest, and provide us with a shared reference schematic .


Schematic referencing:

Off site Access as:

http://i.imgur.com/k2xMB8v.png



73's de Edd


.

Ed,
Those resistors are related to focus.
The intensity issue is totally different!
It is at pin number 3 of the CRT.

DB20Bogen,
Please respond to my previous reply ( #2).

Ed,
Those resistors are related to focus.
The intensity issue is totally different!
It is at pin number 3 of the CRT.

Thanks for the response (and it's finally the weekend and I have some time)
Z Axis has no effect on trace intensity. No change in trace intensity for horizontal modes A or Alt . However in mode B the screen is flooded (entire screen is illuminated) and shows a slight variation in intensity. Also tried adjusting the grid bias control(R851) (per 2235 Service manual) again no effect(trace remains bright).
I have another scope (that was in storage), just plugged it in and does display a signal. It's a Tektronix 549 with a type CA plug in. Most of my equipment has been in storage 15+ years (moving, jobs, family) so I'm still going through and seeing what does and doesn't work. In recent years I've spent a lot of timing writing code and some using a logic analyser (not much hdwe work in the last 15+ years).

 

[DB20Bogen]

.


Sir . . . . . .DB20Bogen . . . . . . (And 'ole Bogen amps don't require this high degree of instrumentation sophistication.)

How about a cold dead set condition and measuring that series string of resistors again as per their resistance readings and ALSO include the one at the very head of the supply on the HV side and the low side of the focus supply as R894 which is being . . . . . guess what . . . yet another 510 K.


Went into my "mule barn" archives and pulled its schematic and then UNITIZED it into one cross page flowing unit, instead of its two pages in the manual.
I think that it will cover all of the situations relevant points of interest, and provide us with a shared reference schematic .


Schematic referencing:

Off site Access as:

http://i.imgur.com/k2xMB8v.png



73's de Edd


.

Thanks for the response, all the 510K resistors are in tolerance. My other scope is a Tek 549 but that's still late 60's

 

[dorke]

DB20Bogen,
You should use the Tek 549 to debug the 2235.

Forgot to ask:
Any effect of A or B intensity knobs? (I assume none,just making sure).

Look at the attached pics
You should check the waveforms with 549 Probe GND to chassis of 2235.
Warning : HV presnt in the area !

1.Check waveform 48 - Before you check with the 549 scope ,use a DMM and make sure you don't have High-Voltage(over 100V) on it!(could be in some fault situation).
2.Check waveforms 47,46,45.

Compare to the pics, and please let us know what you find.