help with oscilloscope model 34

[thermionix]

I haven't read through the whole thread, but it would be pretty sucky to go through all this trouble and find out the CRT is dead.  Do you at least see the heater lighting up?  Assuming it's not obscured by the cathode, socket, yoke or something.

[Rob Strand]

From the part values you sent me this one looks a but suspicious,

R62 560K=185 METER SET ON 2M

Now the measurement was done in circuit and the surround parts could upset the measurement.
The paths in the circuit that would effect it are:  C32 and pin 2 of the CRT.

It could be you didn't wait long enough to take the measurement.  When you have caps in the circuit, especially with high impedances, it can take some time to settle.

Another good practice for measuring in-circuit resistances it to take two measurements.  One with the probe in one direction and one with the probe in the other.   You have to wait for the measurement to settle in each case.

Now, even if C32 had a problem it would not cause the voltage on R57 to be low.

[Rob Strand]

I haven't read through the whole thread, but it would be pretty sucky to go through all this trouble and find out the CRT is dead.  Do you at least see the heater lighting up?  Assuming it's not obscured by the cathode, socket, yoke or something.

I think he mentioned it was lighting up very early in the thread.  Maybe even in his other thread where be bought the equipment. see post #3 and post# 10

[whomeno]

R62 560k = 927
R60 1m  = 1.023
R63  220k =325.4
R57 3.3m = 1.766
R59  1m = .887
C30 .1uf 1600v=19.16
C31 .1uf 1600v=OL

[whomeno]

yes the crt is lighting up at the rear by the plug.

[whomeno]

the last measurements are ohms
do you want me to put it back together and take live voltage with the probe?

[whomeno]

this one was done with old meter "R62 560K=185 METER SET ON 2M"
The last set was with new meter

[whomeno]

The ones i sent by messanger was resister values. done with old meter.
Just got new meter today. glad i got it

[Rob Strand]

the last measurements are ohms

I'm not sure which ones are in ohms as some seem like they are in K or M

R62 560k = 927                 k?
R60 1m  = 1.023                         M?
R63  220k =325.4                        k?
R57 3.3m = 1.766                        M?
R59  1m = .887                           M?
C30 .1uf 1600v=19.16               
C31 .1uf 1600v=OL

do you want me to put it back together and take live voltage with the probe?

If you are confident making the measurements safely we can go ahead.

A couple of things though:
-  You probably want to force you meter to be on the 6V DC range.   At least that way the measurement will be in kV (so 1V = 1000V)   If it's bobbling around the scales it harder to interpret the results.

- Before you measure the HV measure a 200V rail and a 400V rail and make sure you are getting 0.2V and 0.4V measurements respectively.   If not, do not continue as there is something wrong with the setup or the probe.

[Rob Strand]

Maybe consider using you old meter first?
Then repeat with the new if all looks ok?

[Rob Strand]

I haven't read through the whole thread, but it would be pretty sucky to go through all this trouble and find out the CRT is dead.  Do you at least see the heater lighting up?  Assuming it's not obscured by the cathode, socket, yoke or something.

Another really annoying possibility is someone has broken a pin on the CRT.

I wouldn't like to check at this point as we may break it by accident trying to look at it!.

[whomeno]

ok just to be sure where can I find the 200 and 400 v rails

[whomeno]

ok useing C33 for voltage
235v with meter set on 00.00 =.24
set on 000.0  =.2

424v meter set on 00.00 =.43
meter set on 000.0 =.4

useing probe

[Rob Strand]

ok just to be sure where can I find the 200 and 400 v rails

You found some back in post #106.

The 400V rail is from C33A. 

V7pin7   c33A  =  425v
B+a           C33D  =  160v
B+b [V]   C33C  =  348v
B+c [H]   C33B  =  373v

The 400V on C33A and the 160V on C33D would be fine.
It might be less cramped measuring this on the resistors.

You might want to get more exact values for those voltages by measuring with your DMM.
After that measure with the 1.5kV probe and check they match up.

The whole idea is to make sure both measure the same voltage and that nothing has changed since the other day when we checked the 1.5kV probe.   It's a good idea to verify things like 1.5kV probes.

[Rob Strand]

ok useing C33 for voltage
235v with meter set on 00.00 =.24
set on 000.0  =.2

424v meter set on 00.00 =.43
meter set on 000.0 =.4

useing probe

You beat me to it.

Those results look good:
Probe 0.43V => measured voltage = 0.43kV = 430V   (1.4% high)
Probe 0.24V => measured voltage = 0.24kV = 240V  (2.1% high)

[whomeno]

Great, waiting further instructions. sorry I don't spell so good.

[whomeno]

I seen on the bottom of the one schematic you posted. all resistors are 1/2 watt unless marked different.
So I would go with 1 wat to be safe, will this work? will not change any resisters till we get it working.

[Rob Strand]

I seen on the bottom of the one schematic you posted. all resistors are 1/2 watt unless marked different.
So I would go with 1 wat to be safe, will this work? will not change any resisters till we get it working.

Yes, hold off on any resistors replacements at this point.
The test with 9V battery didn't show up anything to be concerned about.

[Rob Strand]

Great, waiting further instructions. sorry I don't spell so good.

OK.
So we will check some of the HV voltages.  I'm purposely not checking the voltage on either side of R63 at this point.  All the other voltages I've marked have some sort of resistance in series with them to limit mishaps.

So,
- Check the ground lead on the 1.5kV probe is attached well to the chassis of the CRO and make sure it won't get knocked off during the measurements.
- Connect the probe to the multimeter COM (-) and meter V(+) inputs.
- Don't touch the meter or the connections during the measurement.
- Set the meter to 6V DC.   Force the range if possible.
- Set the Focus pot to mid position
- Power-up the unit
- Set the Intensity pot to mid position.
- wait about 30 secs to a minute for the unit to warm up
- measure the six voltages marked in blue on the diagram below.
- turn off the CRO.
- remove the mains plug
- wait about 30 secs to a minute and removed the 1.5kV probe ground connector.
- If anything weird happens like smoke, fizzling noises, sounds of arcing. stop the test immediately,
  turn off the CRO and remove the mains plug.   Tell me what happened and we'll take it from there.

[whomeno]

probe is working can test C33 a-b -c-d
getting 0 on all test points


V57 =0
V58 =
V59 =
V60 =
V62 =
VCRT4 =