Help with a Tektronics 2205 , does not display anything

[gkaralus]

tektronics 2205

Hi, I have this scope and I downloaded the service manuals
It does not displays anything, but the power led come on and moving buttons around I can get the trigger led to blink.
When I press the beam finder nothing happen
I checked the voltages from the power supply and they are ok
I checked the horizontal output and it seems ok

I have a hunch that it may be the crt itself
I will test for open filament
Any Ideas or suggestions?
where is the flyback or HV in this thing?
if it is the crt where could I get one? 154-0929-00
Any and All the help is appreciated

 

[E-design]

tektronics blank screen

Turn up the brightness control full. Darken the room and watch screen closely when switching of the scope. If there is any brief flash on the screen then chance is good that CRT is OK and there is another problem with blanking, control signals etc.

 

[gkaralus]

crt 154-0929-00

Ok I did that test and it does not displays anything, room completely in the dark, turned it on and of several times
BUT when when I press the beam finder a smudge lights up in the screen for a second.

Thanks, any more suggestions?

 

[E-design]

Re: Help with a Tektronics 2205 , does not dosplays anything

CRT most probably functional. You should start checking all the CRT voltages. Incorrect Z axis control voltages will blank CRT. Service manual should have all voltages listed on the CRT pins.

 

[gkaralus]

Re: Help with a Tektronics 2205 , does not dosplays anything

Ok.
The filament has 6.7 volts ac ( at the connector in the main board)the manuals don't say how much it should be.
there is another pin that has -1900 v dc , the -1xxx is correct by the manual but I can't distinguish the xxx is correct

 

[E-design]

Re: Help with a Tektronics 2205 , does not dosplays anything

The -1900V would be the cathode voltage. The heater voltage looks normal. Maybe post a GIF type scan of the CRT circuit and voltages so I can give you some hints. I don't have the diagram to look at.

 

[gkaralus]

Re: Help with a Tektronics 2205 , does not dosplays anything

I hope with a pdf works I did a print from one page and did not worked, now I extracted that page and it is ok, sorry

 

[E-design]

Re: Help with a Tektronics 2205 , does not dosplays anything

I have marked parts I would check first for shorts or leakage. The point marked "7C" is very important to have the correct waveform and levels as per the scope diagrams in the manual, otherwise the beam may be blanked and not visible. Unfortunately you will need another scope to check this.

 

[gkaralus]

Re: Help with a Tektronics 2205 , does not dosplays anything

Thanks, the high voltage static burned my multimeter (and froze my keyboard and mouse) So I got a cheap spare multimeter and took these measurements in dc volts:
Q845 Emitter 98.5
Base 97.4
Collector 8.4

Q840 Emitter 0 (ground)
Base .7
Collector 8.4

I am studying electronics on my own, but I don't know how to interpret this ( at least I know the transistors are not shorted)
I place an order for new manuals that should be scanned better. No way I can get access to another scope, unless I can use one of those software that use the sound card as a scope. I have the software.

 

[gkaralus]

Hi, someone sugested me to disconnect the "plates" the teory is that I should get a dot in the center of the screen. Then connect horizontal or verticl circuits to see wich one is failing.
Any suggestions?

 

[E-design]

You could do that to make sure there is not a huge DC offset on the plates, but normally even with such an offset you still see enough screen action during the on-off test in a darkened room. My own guess is that the beam is blanked, from a fault in the DC restoration circuit causing a wrong potential on the one or more grid to effectively cutoff the beam.

 

[gkaralus]

Hi , I got the new schematics, a lot better than the other ones.
Disconnected the input of the horizontal amplifier. and also the input of the vertical amplifier, no difference. no dot in the center of the screen,
Then I disconected the crt from the horizontal and vertical amplifier
Also nothing in the screen
I replaced the previus pdf of the horizontal amplifier and here is the schematic for the vertical amplifier
And I tried to measure the resistance of the crt filament at the mainboard and it is open , the only thing that can save me is a problem in the connector in the back of the crt

 

[gkaralus]

I got it working!!
It seems someone already disassembled the scope once, and when he put the crt back in place it pushed the crt connector backward so nothing was realy connected to it.

 

[E-design]

Just shows, never overlook the obvious!