Hi!
This is my first post here, so maby I should introduce my self; I'm from sweden, on my last year studying to become an EE but I've hade electronics as a hobby many years before I started my education.
A couple of days ago I bougt these two nice, old (1977) HP scopes really cheap, one works perfectly, and one is broken. When in sweep mode I get no x movement on either channel, but when in x/y mode i get movement on the x axis, indicating that the x-amplifier works. The x possition adjustment is also off, letting me only move on the right half of the screen.
Luckily I also got the service manual, so I set up the scope and fed it a sine as mentioned and started probing it.
It seems the problem is in trigger mechanism, this consists mostly of TTL-logic, which thankfully is pretty easy to meassure. But I'm having problems with isolating the source of the malfunction, since the circiut is pretty messy with a lot of feedback paths (combination of logic and analog circuitry).
I got a scanned version of the manual, which can be found here: https://tinyurl.com/7slcrrz
I also marked a few testpoints and suspected areas in the schematic of the trigger generator:
**broken link removed**
The testpoints, with reference waveforms from the manual that I tested are marked with green or red depending on working status, the green ones have a waveform, the red ones are flat (DC).
The JK-flipflop U7, marked with pink boxes, was one suspected component, it controlls the nand-gate where the waveforms doesn't get through. But I tried and manage to set it by pulling some of its pins low, so I don't thik It's here.
The strange latch U8, orange box. Doesn't giva an output but it seems to be controlled from U7.
The light blue box contains the chop-oscillator, this is what alternates between A and B to display both at the same time i believe. This is completly dead, no matter how i set the times/div and A/B switches (witch suppusedly changes its speed / turns it off). Could this some how cause the trigger to malfuncion or vice versa? I'm having a hard time figuring that out.
The most promising error source here is the three caps C29, C30 and C47, marked with red circles, C29 / 30 are large tantalum caps (says 1000, = 1000uf or 1000nf??). But I don't have the tools to measure them in circuit (and probably not out either).
I should really appreciate some professional help here, before I completly dissassemble the scope to do more thorough meassurements / try changing components.
I should also point out that all supply voltages are stable and good, no ripple, so no bad caps in the PSU.
Please have patience with any spelling errors since english is not my native language
This is my first post here, so maby I should introduce my self; I'm from sweden, on my last year studying to become an EE but I've hade electronics as a hobby many years before I started my education.
A couple of days ago I bougt these two nice, old (1977) HP scopes really cheap, one works perfectly, and one is broken. When in sweep mode I get no x movement on either channel, but when in x/y mode i get movement on the x axis, indicating that the x-amplifier works. The x possition adjustment is also off, letting me only move on the right half of the screen.
Luckily I also got the service manual, so I set up the scope and fed it a sine as mentioned and started probing it.
It seems the problem is in trigger mechanism, this consists mostly of TTL-logic, which thankfully is pretty easy to meassure. But I'm having problems with isolating the source of the malfunction, since the circiut is pretty messy with a lot of feedback paths (combination of logic and analog circuitry).
I got a scanned version of the manual, which can be found here: https://tinyurl.com/7slcrrz
I also marked a few testpoints and suspected areas in the schematic of the trigger generator:
**broken link removed**
The testpoints, with reference waveforms from the manual that I tested are marked with green or red depending on working status, the green ones have a waveform, the red ones are flat (DC).
The JK-flipflop U7, marked with pink boxes, was one suspected component, it controlls the nand-gate where the waveforms doesn't get through. But I tried and manage to set it by pulling some of its pins low, so I don't thik It's here.
The strange latch U8, orange box. Doesn't giva an output but it seems to be controlled from U7.
The light blue box contains the chop-oscillator, this is what alternates between A and B to display both at the same time i believe. This is completly dead, no matter how i set the times/div and A/B switches (witch suppusedly changes its speed / turns it off). Could this some how cause the trigger to malfuncion or vice versa? I'm having a hard time figuring that out.
The most promising error source here is the three caps C29, C30 and C47, marked with red circles, C29 / 30 are large tantalum caps (says 1000, = 1000uf or 1000nf??). But I don't have the tools to measure them in circuit (and probably not out either).
I should really appreciate some professional help here, before I completly dissassemble the scope to do more thorough meassurements / try changing components.
I should also point out that all supply voltages are stable and good, no ripple, so no bad caps in the PSU.
Please have patience with any spelling errors since english is not my native language