Need help with a Tektronix 2215A O-Scope problem

[Ken]

I have a 2215A Tektronix oscilloscope that has a problem. The CRT lights up
but it displays a square lighted area (about 3" wide X 2" high) without any
input on either channels, not a straight line. Although the display can be
moved left, right, up and down the focus control does nothing. I ordered a
service manual for it tonight but thought some of you may have some idea
where to start. I am thinking HV may be way off or the CRT may be bad
although it has a bright display. I have another scope to use to work on it
with. The time base and the vertical amplifier setting don't effect the
display. The intensity control works as it should. By pressing the Beam
Find the display shrinks horizontally but not vertically. The display has
some jitter when first turned on but settles down after some time. Any
insight into the problem will be appreciated.

Thanks,
Ken, WS4V

 

[Michael A. Terrell]

I have a 2215A Tektronix oscilloscope that has a problem. The CRT lights up
but it displays a square lighted area (about 3" wide X 2" high) without any
input on either channels, not a straight line. Although the display can be
moved left, right, up and down the focus control does nothing. I ordered a
service manual for it tonight but thought some of you may have some idea
where to start. I am thinking HV may be way off or the CRT may be bad
although it has a bright display. I have another scope to use to work on it
with. The time base and the vertical amplifier setting don't effect the
display. The intensity control works as it should. By pressing the Beam
Find the display shrinks horizontally but not vertically. The display has
some jitter when first turned on but settles down after some time. Any
insight into the problem will be appreciated.

Thanks,
Ken, WS4V

It sounds like power supply problems.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Jim Yanik]

It sounds like power supply problems.

That is always the first place to check anyways. One must verify the low
voltage supplies before anything else.Everything else builds off those LV
supplies.
A display shrunk in both X and Y axis could be loss of CRT anode
voltage,but it would also be dimmer than normal.Focus would naturally be
affected.

 

[tekamn]

HV seldom goes such a way of in 2213/2215 scopes to my repair
experience. LV supply is more probably the cause.

Go for a service manual ( bama.sbc.edu for download or mirror).
2215/2215A/2213 are very similar in pwr supply section. So any manual
will of of help.

check for bad/dry caps. replace. The fault sympthoms you describe are
most often due to one or more LV supply voltages out of range.


hth,
Andreas

 

[Jorgen Lund-Nielsen]

That is always the first place to check anyways. One must verify the low
voltage supplies before anything else.Everything else builds off those LV
supplies.
A display shrunk in both X and Y axis could be loss of CRT anode
voltage,but it would also be dimmer than normal.Focus would naturally be
affected.

Hi Jim,

low HV leads to the opposite effect,
if the HV goes low, the electron beam gets weaker and it
is easyer to deflect, the display expand and is dimmer than normal.
In the old TV-Set times with a HV-tube rectifier, which sometimes goes
bad, the TV-Set had the "magnifying glass" - effect.
If you turn the intensity high, the picture vastly expands.
I would expect that the shrunk display comes, as you stated, from the
LV-supply. Maybe in the beamfinder-circuit could be something wrong
but not very likely.

Jorgen

 

[Michael A. Terrell]

Hi Jim,

low HV leads to the opposite effect,
if the HV goes low, the electron beam gets weaker and it
is easier to deflect, the display expand and is dimmer than normal.
In the old TV-Set times with a HV-tube rectifier, which sometimes goes
bad, the TV-Set had the "magnifying glass" - effect.
If you turn the intensity high, the picture vastly expands.
I would expect that the shrunk display comes, as you stated, from the
LV-supply. Maybe in the beamfinder-circuit could be something wrong
but not very likely.

Jorgen

I doubt that you can tell Jim anything about Tek scopes that he
didn't see in the 20 some years he worked for Tektronics at their
Orlando repair center.


The "Blooming" on old TV sets was due to the poor regulation. As the
HV rectifier tube aged, the voltage drop increased. The starved the CRT
of the current it needed during the active display times and distorted
the image. The HV returned to normal during the retrace and blanking
intervals. The CRT needs a clean, stable second anode supply if you
want a crisp, clear image.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Jim Yanik]

I doubt that you can tell Jim anything about Tek scopes that he
didn't see in the 20 some years he worked for Tektronics at their
Orlando repair center.

No,I'm not infallible.I make mistakes like anyone else.
although I've never seen a TEK HV multiplier only be low in output V,they
usually fail by loading the HV osc,or no V at all.(open)WE never even tried
to measure them;if the CRT made a fat spark when shorting the anode lead to
GND,then the HV mult works.

If the Anode V is low,the Cathode V is probably also low;then the display
spreads out.

Minor peeve;it's TektroniX,no 'C'. ;-)

 

[Michael A. Terrell]

No,I'm not infallible.I make mistakes like anyone else.
although I've never seen a TEK HV multiplier only be low in output V, they
usually fail by loading the HV osc, or no V at all.(open)WE never even tried
to measure them; if the CRT made a fat spark when shorting the anode lead to
GND, then the HV mult works.

I never said that you were, but a TV CRT isn't a good comparison to a
scope CRT, and I am sure that you have worked on more scopes than most
people who pop in here with a question, or an off the wall answer. ;-)

You consistently give good advice and take your time to try and help,
which is more than a lot of others will do.

If the Anode V is low,the Cathode V is probably also low;then the display
spreads out.

Minor peeve;it's TektroniX,no 'C'. ;-)

And no 'S' at the end, either ;-)

I know. Give me a break. I was posting after getting up sick in
the middle of the night. I couldn't get back to sleep and was trying to
get caught up on the newsgroups. I just forgot to hit the spell checker.

--
Jim Yanik
jyanik
at
kua.net

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Jim Yanik]

I never said that you were, but a TV CRT isn't a good comparison to
a
scope CRT, and I am sure that you have worked on more scopes than most
people who pop in here with a question, or an off the wall answer. ;-)

You consistently give good advice and take your time to try and
help,
which is more than a lot of others will do.




And no 'S' at the end, either ;-)

I know. Give me a break. I was posting after getting up sick
in
the middle of the night. I couldn't get back to sleep and was trying
to get caught up on the newsgroups. I just forgot to hit the spell
checker.

I was up all night,too;a couple of thieves tried to break into my Integra
at 3:15AM,but the alarm warning triggered(not the full alarm),I looked out
a window and saw them shining a flashlight into the car and walking around
it,and I went out and chased them off,got a partial description of their
car to give to the police.After that,I couldn't fall back asleep.

It's unfortunate that I could not just shoot them.(legally)

 

[Michael A. Terrell]

I was up all night,too;a couple of thieves tried to break into my Integra
at 3:15AM,but the alarm warning triggered(not the full alarm),I looked out
a window and saw them shining a flashlight into the car and walking around
it,and I went out and chased them off,got a partial description of their
car to give to the police.After that,I couldn't fall back asleep.

It's unfortunate that I could not just shoot them.(legally)

--
Jim Yanik
jyanik
at
kua.net

Glad to hear you were able to run them off. Not sleeping is a daily
thing for me.

Too bad it wasn't parked inside your garage.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Jim Yanik]

Glad to hear you were able to run them off. Not sleeping is a
daily
thing for me.

Too bad it wasn't parked inside your garage.

Apartment complex. I dream of having a garage.

 

[Michael A. Terrell]

Apartment complex. I dream of having a garage.

I have a four car garage, but its full of tools and old electronics.
I have to leave both pickup trucks in the driveway.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida