Repair Tips for Hitachi V-212 oscilloscope

[bandu]

Hello ,all guys in EDABOARD,
I have a problem in my oscilloscope ,it's HITACHI V-212,got it from my uncle ,all are working but
FOCUS control does not work ,visible broad horizontal line, can not control, I am fear to touch ,because
of high voltage,if anybody have an idea ? which section I have to repair exactly.
Thanks ,Bandu

 

[betwixt]

I don't know that model but from the description you give, it is a very common fault on CRT oscilloscopes. I think you will find that the focus voltage comes from a chain of resistors and one of them has gone open circuit or increased in value significantly. The result is the wrong voltage on the focus anode and the control having little or no effect.

A schematic would help.

Brian.


Just downloaded the manual - it is almost certainly either R1019 (330K), R932 (2.2M) or R933 (15M) that is at fault. I would try R933 first, if you can't get a 15M high voltage resistor, use 2 x 4.7M and 1 x 5.6M in series, it should be close enough.

Brian.

 

[bandu]

OK thanks betwixt, I found it and repair,that 470k resister was open .
Thanks bandu

 

[bandu]

hai, all my friends in EDABOARD,
I have a problem in my Hitachi V-212 oscilloscope, it's not holding the wave form in horizontal direction, I tried my best with all controls ,and struggled to hold it ,but which is not holding ,in my knowledge ,i think it should be in sync circuit ,I don't know weather it's wrong or right ,if anybody have an idea or experience with this problem ,please help .
Thanks Bandula.

 

[D.A.(Tony)Stewart]

Does it trigger in normal mode? If not using AC couple or DC then check caps for ripple on supply, then follow signals on p66 to p67

 

[bandu]

OK thanks Sunny , I will try it and ,comeback to you .
bandu

 

[bandu]

Dear Sunny,
I replaced the caps in power supply(c1101,c1102,c1111,c1121) and also replaced the R527 10 Meg resistor in (sweep gen ) ,it's gone high,and associated with sweep vernier ,little bit improve that wave form rolling ,but difficult to hold.I didn't find P66,P67 it's in which section ?,any way appreciate your kind cooperation .and hope your further help.
Thanks bandu

 

[bandu]

Dear friends in edaboard,
Still have the same problem in my HITACHI V-212 oscilloscope,wave form
is not holding on horizontal direction , sweep vernier section does not work
properly I replaced the caps in power supply(c1101,c1102,c1111,c1121) and also replaced the R527 10 Meg resistor in (sweep gen) circuit,still no
solution ,if anybody has an idea?
Thanks bandu

 

[bandu]

Dear all my edaboard friends,
I solved that my HITACHI V-212 oscilloscope,wave form rolling problem by my self , I slightly turn the trigger level center control (RV420) that's all.
it's solve the problem .
Thanks bandu.

 

[TexasTwister]

more Repair Tips for Hitachi V-212 oscilloscope

[Howdy,
I am knew to this message board and recently purchased this same scope off eBay along with a curve tracer to fix arcade video boards I also purchased off eBay for my own personal use. Anyway it appears CH1 X input is not functioning so it is worthless with the curve tracer so I have downloaded the service manual but thought I would ask what is the best starting point before I open up the scope.

Thanks so much,

TexasTwister