Products > Test Equipment
HP 1741A oscilloscope - restoration project
Omicron:
--- Quote from: tekfan on October 18, 2011, 07:29:56 pm ---
--- Quote from: BravoV on October 17, 2011, 07:04:32 am ---Btw, what Jim Williams pulse generator ? Link ?
--- End quote ---
http://cds.linear.com/docs/Application%20Note/an47fa.pdf
Page 93-95
--- End quote ---
Be careful, the pulse generator described in this app note is not suitable for rise time measurements. I think this has been discussed on this forum before. The pulse it produces is too narrow. For a correct rise time measurement the scope trace MUST be able to reach the full amplitude of the step input. If the input pulse disappears before the scope trace has achieved the true amplitude of the input signal then your reading will be wrong (i.e. far too optimistic). The pulse from this generator is so fast even a 400MHz scope has no hope at all of showing it's real amplitude.
Jim himself undoubtedly knew all this as he made several modifications to the pulser in later app notes to achieve a wider output pulse.
tekfan:
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.
FenderBender:
Awesome work. These scopes really look like great pieces of equipment. I was debating between one of these and a old Tek scope. I wound up going with the Tek, but this is a lovely piece of equipment.
BravoV:
Great finding and awesome restoration job as usual, thanks Tekfan.
Btw, about this particular model 1740A, does it have custom ics ? Cause I'm being offered the same exact model by local surplus shop here.
tekfan:
--- Quote from: BravoV on December 29, 2011, 09:31:03 am ---Btw, about this particular model 1740A, does it have custom ics ? Cause I'm being offered the same exact model by local surplus shop here.
--- End quote ---
The 1740A has four custom ICs. Two hybrids. One for the vertical preamp and the other for the vertical output amp and two ICs in the trigger circuit. One for main sweep and the other for triggered delayed sweep.
I've never had any of these fail no matter how dirty or misused the scope was. The primary problem seem to be the shorted rectifiers.
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