Products > Test Equipment
HP 1741A oscilloscope - restoration project
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mayeri:
Unfortunately, my another oscilloscope is broken too. 
EMG 1568/2A (2x50Mhz). Search it with Google, it is interesting look at him. This is one of products of an former, now defunct Hungarian electronics factory, it it called EMG.  Power supply also was defective, but I am still hunting for the fault because the electron beam is missing.
Do you know? I would not be so lucky…
timjimbaker:

--- Quote from: tekfan on December 28, 2011, 11:48:15 pm ---Recently I got another HP scope. This time an HP1740A. This was on it's way to the dump at my school. The sides were unscrewed and put beside the scope so obviously someone tried to repair it. It is very similar to the 1741A storage oscilloscope. The 1740A is a dual channel 100MHz analog oscilloscope with delayed time base and 1mV/div maximum sensitivity (5mV/div full bandwidth).

This is basically how it arrived. It would blow the fuse when turned on.


After a bit of searching I found two rectifiers shorted. This seems to be a common problem in these scopes.


Then I found two burned resistors on the Z axis board.


Looks like the ceramic capacitor went short circuit and caused the two resistors to blow.


Replacing the resistors allowed the Z axis amplifier to unblank the beam and suddenly a trace appeared.


The time/div switch shaft was also worn. Looks like this scope had a lot of use.


Contacts of the time/div switch are still in great shape but the center hole where the shaft goes trough
is worn so that the contacts on the switch are misaligned with the contacts on the PCB.
This caused severe timing errors in the horizontal time base.


--- End quote ---

Hey Guys, this is my first post. This is a great forum, I hope to frequent it now that I've found it...

I need a bit of help. Just bought a 1740a. It's in decent shape except for one thing. Someone must have lubricated the time division switch with something they shouldn't have many years ago. Basically what ever it was has broken down and turned to glue... I fired some deoxit in there and it freed up the switch. I figured that had fixed the problem. The next day, the switch had re-glued its self again. I dismantled the assembly and took out the pcb that is sandwiched by the two halves of the  switch. The glue/lube cleaned up nicely. My problem is that a few of the contacts have been pulled out of their slots on the switch. Tekfan was kind enough to post all of those great photos of his restoration. One of which is one half of the switch. It shows where the contacts for that side belong. I was hoping someone may have a photo or diagram of the other half so I can make sure the contacts get put back to where they belong.

Thanks. Best regards, Tim.
tekfan:

--- Quote from: timjimbaker on February 07, 2013, 07:31:19 pm ---I was hoping someone may have a photo or diagram of the other half so I can make sure the contacts get put back to where they belong.

--- End quote ---

I'll dismantle the scope sometime during the weekend and post the pictures.

Luckily they didn't use multi-wafer switches. That would be a real pain to clean up.
HackedFridgeMagnet:
I have a 1742 and a 1725 both of which need to be opened at some stage.
But from my recollection if you look carefully you should be able to see from which positions the contacts had been mounted. You can see small wear marks.
Hopefully you don't have any broken leaf springs. I have one broken one that I fixed with a banana plug and an angle grinder but It isn't a long term solution. I have some watch spring steel that I am going to use to fix it a bit more nicely. One day.
lowimpedance:

 
.
--- Quote ---Someone must have lubricated the time division switch with something they shouldn't have
--- End quote ---


The lube/GLUE like goop is whats left of the original HP lube used on these series of CRO's.
Does not age at all well as you have found, how ever its easily removed and new lube applied.
I have cleaned half a dozen of these series oscilloscopes with this 'glue issue', and none of them
had been touched since new.
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