No picture

[Silver Surfer]

My Zenith Model SG2037W has lost its picture. Sound is fine. Don't see any
glow from the neck of the picture tube. There is a burn mark on one of the
wires leading to the circuit board mounted to the neck of the picture tube.
The burn is evidently because the wire was lying against the high voltage
lead which has a corresponding burn mark. Does anyone have a schematic of
this set they could lend me?

 

[Mr TUBEAMPS]

check the EHT transistor hasent gone open
or short.

 

[Silver Surfer]

Sorry for my ignorance on this subject, but what does EHT stand for? I
think I know that HOT stands for horizontal output transistor, but EHT has
me stumped. Thanks.

 

[Silver Surfer]

Where would you recommend that I buy a service manual for this set?

Sams has the paper type as well as a downloadable file. Do you have any
trouble working from the electronic manuals? When they are printed are they
equivalent to the original paper documents?

 

[James Sweet]

Sorry for my ignorance on this subject, but what does EHT stand for? I
think I know that HOT stands for horizontal output transistor, but EHT has
me stumped. Thanks.

EHT = extremely high tension, high voltage, HV, etc. You said the set is a
Zenith though which immediately says don't spend too much time/effort on the
thing. Is this one of the direct view sets that usually gets a bad CRT?

 

[Silver Surfer]

Well, the reason I'm fooling with this set is that it has become a challenge
for me. Up to now it has given excellent service. Bought it back in '91
for the bedroom so I would have something to occupy my time while recovering
from old fashioned type gall bladder surgery.

I'm retired now, so there is time available to work on this beast. It might
whip me, but not without a good fight.

Trouble is I'm an amateur tinkerer; however, I do know that the pros hang
out on this board and are an enormous help to "shade tree" technicians like
me. Thank goodness there are people like you out there who are willing to
share their considerable knowledge and experience with the rest of us.

 

[James Sweet]

Well, the reason I'm fooling with this set is that it has become a challenge
for me. Up to now it has given excellent service. Bought it back in '91
for the bedroom so I would have something to occupy my time while recovering
from old fashioned type gall bladder surgery.

I'm retired now, so there is time available to work on this beast. It might
whip me, but not without a good fight.

Trouble is I'm an amateur tinkerer; however, I do know that the pros hang
out on this board and are an enormous help to "shade tree" technicians like
me. Thank goodness there are people like you out there who are willing to
share their considerable knowledge and experience with the rest of us.

If it's a 25" it's entirely possible the CRT has shorted and taken something
else out, guess it won't hurt to fiddle with it if you want though, just
beware dumping money into parts that may blow up in short order.

 

[Silver Surfer]

This is a 20" TV. Don't know if its CRT is vulnerable to the shorting
problem you mentioned or not.

It appears that the filament(s) is(are) not open; however with the socket
off the tube there is continuity from the filament (pins 9? and 10?) to pin
12. Doesn't look like pin 12 does much. Not sure why there is continuity
there.

 

[Silver Surfer]

Back in business. A resistor that seems to be for supplying startup 18-volt
power to the horizontal output stage was burned open. Burned beyond
recognition. Actual circuit had a diode in series with the resistor in what
appears to be a factory modification. Sams schematic showed only a 470 ohm
resistor. Zenith schematic showed only a diode. Took a wild shot and put
in a 120 ohm resistor in series with diode. OK now.

 

[Mark D. Zacharias]

Back in business. A resistor that seems to be for supplying startup
18-volt
power to the horizontal output stage was burned open. Burned beyond
recognition. Actual circuit had a diode in series with the resistor in
what
appears to be a factory modification. Sams schematic showed only a 470
ohm
resistor. Zenith schematic showed only a diode. Took a wild shot and put
in a 120 ohm resistor in series with diode. OK now.

Often when I'm in this situation, I'll put in a flameproof resistor chosen
to be dissipating, say, 1/10 watt for a 1/2 watt resistor. Any serious
malfunction will take out the resistor safely. If the resistor is feeding a
voltage regulator, this can be tricky though - the regulator will have to
dissipate more power if the resistor value is too low.
Actually, the same would apply to the load circuit if the voltage is
unregulated. Hmmm.


Mark Z.