Hitachi Oscilloscope problems

[doityoureself]

I got this scope really cheap and I know why now, but It will be interesting to see if it can be fixed, or I should say if I can fix it. I do know the scope has been taken decent care of and no signs of abuse.

With DC voltage on channel 1 two vertical lines appear instead of two dots,(pic 2nd from left)..........when I set the scope to trigger the signal on channel 1 (sorry I cant add picture) it looks like">>>>>>>>>>>>>>>>>>>>>>>>" instead of "======================"

channel 2 beam(or dot) looks fine and I can adjust it out sharp and clear.(pic 1)

(this problem has been resolved, thanks to "Steve"...had bad leads) Now the second problem is on channel 2 testing a/c votage, when I touch the probe to a 110vac supply I get an odd readout(pic 3) until I slightly move the probe off of the test point anywhere from 1/8in, to 2in.(pic 4). Can anyone please tell me what they might think is going on, I know all of the dial settings seem to be working properly, I have taken the cover off and tweaked all of the potentiometers to see if any improvements could be made with no success. I have a feeling I may have some filter caps bad or other component problems as they are problems isolated to each induvidual channels. thanks for ANY input.

 

[(*steve*)]

Are you saying that the 4th display is what you get if you move the probe *away* from the signal source, and that the third is with it connected?

I would cross my fingers and suspect the part which has the most mechanical stress placed on it -- the probe and lead. See if you can beg borrow or... hire,,, another probe.

Do the probes match this scope? does the scope have a calibration signal? What does this look like?

Have you tried wiggling the cable and seeing if this affects the display?

Also, for reference, what make and model is this scope?

 

[doityoureself]

oscilloscope problems

Hitachi V203F 20mhz dual channel, 1x to 10x probe, on the problem with the fuzzy distorted signal as in the next to last picture(3rd from right in

first post), yes the probes are original and worn bad, wiggling at the probe end does produce bad interference so you nailed it. Can I just buy a

probe obviously that has the same input connections, for 20mhz and 10x multiplier? Or does the mhz and/or multiplier matter? This definitly gets

me at least one good working channel and a useable scope. thanks "Steve" taking the time to read and give your thoughts. Now if I can get any

hits on what could be making my channel 1 beam look like a "l" instead of a "." I will be in business. thanks

 

[(*steve*)]

The first thing is to swap the probes over and see if the problems switch from one channel to the other. If so, then all your problems are due to the probes.

If not, then at least you have one good channel.

In general you'll want a probe with the same (or slightly higher) bandwidth as your scope. They should suit the input impedance of your scope, if it is 1M and 20pf, then your scope is the same as probably 90% of scopes on the market.

I would look for a switch able x1, x10 probe first (since that is what you have now). My second choice would be a x10 probe.

Probes can be *very* expensive. But there are places on the net where you can get very cheap (and probably reasonably nasty) probes. I haven't bought any from here, maybe someone else has and can comment on the quality.

The probes I have are HP10042A's that were quite cheap, but still cost me about 10% of the price of my scope (each).

Bad probes can degrade the performance of your scope (as you've seen) but sometimes not so obviously.

The user's manual can be found here. It's probably worth getting it if you don't have a manual.

There are procedures in there for basic fault finding and setup that you should follow.

It looks like you have some trace rotation, I haven't checked, but the manual may tell you how to correct this too.

 

[doityoureself]

I just wanted to follow up on my progress, I had some great luck with this old unit

after I spent $10 on a can of electrical cleaner(the kind for pcb's with no lubricant), the

inside of the cabinet was really dusty, so I took a air hose with a nozzle and carefully

blew as much dust as I could out of the circuitry and around the crt. Then I took the

electrical cleaner and with the unit standing on its back with the knobs standing strait

up, I started at the knobs, sprayed out around the front of them, working knobs back

and forth while spraying, then moved to the back of the knobs and worked my way

all the way down to the back where the cord plugs in. Virtually rinsing down all the

dust out and letting the liquid drain out the back. I then let it set for 24hrs., plugged it

in, read the manual online, and with a little adjustment everything works great. I read

that dust on the inside, especially on the crt can cause static to build up and cause

some of the exact problems I was having. I still could use a set of new probes but it

was not my main problem.


I would have to advise anyone who uses the electrical cleaner to be sure to read

the directions and do not plug any power back in until it has dried completely, also be

careful with some of the older plastic parts as it may eat away at it pretty agressively.

 

[Richard King]

I got this scope really cheap and I know why now, but It will be interesting to see if it can be fixed, or I should say if I can fix it. I do know the scope has been taken decent care of and no signs of abuse.

With DC voltage on channel 1 two vertical lines appear instead of two dots,(pic 2nd from left)..........when I set the scope to trigger the signal on channel 1 (sorry I cant add picture) it looks like">>>>>>>>>>>>>>>>>>>>>>>>" instead of "======================"

channel 2 beam(or dot) looks fine and I can adjust it out sharp and clear.(pic 1)

(this problem has been resolved, thanks to "Steve"...had bad leads) Now the second problem is on channel 2 testing a/c votage, when I touch the probe to a 110vac supply I get an odd readout(pic 3) until I slightly move the probe off of the test point anywhere from 1/8in, to 2in.(pic 4). Can anyone please tell me what they might think is going on, I know all of the dial settings seem to be working properly, I have taken the cover off and tweaked all of the potentiometers to see if any improvements could be made with no success. I have a feeling I may have some filter caps bad or other component problems as they are problems isolated to each induvidual channels. thanks for ANY input.

Lets make it clear...I'm no tech....BUT I see from the pics that your TRACE ROTATION is out of adjustment. Really easy fix too...that hole drilled in front panel...usually in bottom left or by the power button....rotate it gently with a small screwdriver...say the one used to attenuate your probes....until the waveform upper and lower signals align as close as possible to any of the HORIZONTAL LINES on the screen...you may have to rotate the POSITION button for the channel you are using. First off....it seems like your scope needs calibration....download a manual in pdf form and do what adjustments you can if you don't have a function generator and it will get a few things inline for you. BE CAREFUL NOT TO WIGGLE OR PRY COMPONENTS TOO MUCH WHILE TRYING TO GAIN ACCESS TO TRIM POTS FOR ADJUSTMENTS....YOU MAY BREAK SOMETHING IMPOROTANT AND BE IN THE SAME BOAT AS ME....BROKEN SCOPE!!!! GOOD LUCK...