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Hitachi V1100A 4 channel 100 mhz oscilloscope

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steve dove

New Member
Hello all
I have a Hitachi V1100A oscilloscope,that has had a fault that had been kicking in,after approx 10-15 mins operation,it loses 100 volt dc supply rail.,drops down to its ajacent which is 35-40
i am an electronics engineer by trade,i have to say though this one has run me somewhat
ragged,i disconnected the external points where this voltage goes,still same result.
the issue when it first showed up,took longer to occur,but got to happen over a shorter
period,then would not show crt trace at all,same with cursor,i have considered the possibility of thermal protection in the power transformer,this scope comes with user manual that has all the cct layout,schematics inside,i can find nothing re owner faults with these anywhere,my feeling is the problem is either in the rail mentioned,or poss thermal cut,the schem showing power transformer shows the windings,but no indication of thermal protection,so quite possible does not have it,if anyone has sufffered likewise problem with this type or one in this model range,please get in touch i would like to repair it,is in very good condition,have had it since new in box,still have all the original Hitachi packaging,has not had a great deal of use,so if repair can be done,likely go on years it has a lot of features,on screen cursor measurement etc,i dont want to bin it,but if nothing comes of this posting,i may offer it to someone who can bring it back to good order,crt is perfect fix the fault and thats it,only other point was one of the panel pots needed its fixing nut tightening.
rgds steve
 
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JimB

Super Moderator
Most Helpful Member
Welcome to ETO.

,this scope comes with user manual that has all the cct layout,schematics inside
It would help if you could scan the appropriate page of the schematic and post it here as an attachment so that we could see for ourselves before making wild guesses.

JimB
 

steve dove

New Member
hello jim
how you doing thanks for replying.
i have spent a long time doing diags on this,and not had any result as yet,the book with schem
is at my workshop (i think) if at home then i can sort the scan sooner
cheers fella
 

steve dove

New Member
hello again jim
if you type into google hitachi v1100A service manual,2nd down i am seeing download
for owners manual,which i checked out,and there it all is,page 76 (power supply) PEF-675,690,707
shows the 100 vdc supply 1st winding at near top centre of page,P1501 from that connector pins 1&2
thanks steve
 

JimB

Super Moderator
Most Helpful Member
A quick google revealed this, if it helps ..
Well that works badly, for me anyway.
Stuffit complains that it wants part 2, and when I cannot provide it, it just goes off in a huff.

JimB
 

Musicmanager

Active Member
There are 6 parts to that manual ... .. but for some reason ETO will only upload one at a time ..



* Attachments deleted *
 
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steve dove

New Member
jim
did you see the power section in question,from what i can see with the loading
from the boards supplied removed,that should sit at 100vdc ok a little higher
with no load,the components seem to be ok,this is why i think it could be a
thermally protected winding,i may of missed something pulling it down,and
will check again,but if i find nothing i would have to say the winding is suspect
i measured it directly after it shut down the last time,and pins 1&2 of p1501 from
supply winding were indicating o/c when i checked with DVM,if transformer has
failed on that winding,then i wont go any further,for one where will i find a transformer ?
and buying another scope probs a sensible option,so if that is how it pans out,then i will
offer this one out,to someone who has whatever is needed to fix.
cheers
steve
 

JimB

Super Moderator
Most Helpful Member
did you see the power section in question
No. after the downloading failure I went off (in a huff ?) and have been doing other things this afternoon.
I will have a look later.

JimB
 

Musicmanager

Active Member
Ok..

You need to save each section together in a folder and then unzip Pt 1

I have the PDF but it is too large for ETO


S
 

JimB

Super Moderator
Most Helpful Member
OK, I have the manual now.

Looking at the power supply schematic...

Before the 130v supply collapses, measure the voltage at the following points:

P1501 pins 1 and 2

C1501 + and - terminals

TR1503 Emitter, Base, Collector. (measure with one probe of the voltmeter on the +45v point.

When the 130v collapses, measure again and let us know the results, before and after.

JimB
 

steve dove

New Member
hello jim
when measured off pins 1&2 of p1501,i read open winding on the pwr transformer,this may be due to
thermal cutout in the winding,schem does not indicate this,so maybe or not the case,if it is the supply
to 100v dc psu stage,down due to winding o/c then game over doubt will find a replacement transformer.
rgds steve
 

JimB

Super Moderator
Most Helpful Member
when measured off pins 1&2 of p1501,i read open winding on the pwr transformer
Depending on exactly how and where you made the measurement, it may be worth looking at the connector pins and the solder joints where the connector is fixed to the circuit board.
Also look at the wires from the transformer, how they are crimped/soldered to the connector pins.

,this may be due to
thermal cutout in the winding
If there was a thermal cutout in the transformer, I would expect it to be in the primary winding.

if it is the supply
to 100v dc psu stage,down due to winding o/c then game over doubt will find a replacement transformer.
I would agree with that.
It may be worth looking on the likes of e-bay for a scrapper with a good transformer, other than that - tough.

JimB
 

steve dove

New Member
jim
i agree re thermal cut situ primary usually is fav but what was going on
with this hitachi scope,gave impression 100 vdc feed was being lost,i actually
measured from the plug,coming direct from transformer winding,poss a fracture
in one of the wires from transformer,or even a bad connection,actually to the winding.
i will recheck during this week,would not surprise me,if one of the latter points turn
out to be the issue. cheers for now Steve
 
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