Products > Test Equipment
HP 1741A oscilloscope - restoration project
lowimpedance:
--- Quote from: jeno on May 03, 2021, 06:48:18 pm ---I finaly managed to fix the power supply. All the voltages are oke, when the LVPS is isolted from the rest of the scope, but when I connet it I see no trace, the LEDs are working, and the 48v rail drops to zero. Can I get in contact whits someone for help, or some tips, what can cause that? Thank you.
--- End quote ---
So the whole power supply is working when isolated from the rest of the chassis?. And only the 48V rail collapses when reconnected, all others remain in spec.?.
OK, try loading the 48 V rail with suitable values of resistance to see if it can deliver a decent amount of current (within its current limit of course, ~400mA ? i guess) without the rail collapsing.
That will test its operation and thus if any transistors/components etc are still faulty. Check the other passive are in spec.
If it is working correctly there is a short somewhere in the scope on that rail. best to use the interconnecting diagram
in the manual (page 8-48 to 8-50) to see where the 48V rail is routed to and then isolate those modules and measure for shorted components, ie transistors, cap's etc.
Did you repair the Horizontal O/P stage.
jeno:
I found out thet there is problems whit A7 as well as A17. On the A7 board U2 (that shiny gold one) is getting warm, removing it does not change the current draw. But I cant find any schematic for thet board to trace out what can be problematic, any ideas? Later I will move on to A17
lowimpedance:
--- Quote from: jeno on May 04, 2021, 08:12:34 pm ---I found out thet there is problems whit A7 as well as A17. On the A7 board U2 (that shiny gold one) is getting warm, removing it does not change the current draw. But I cant find any schematic for thet board to trace out what can be problematic, any ideas? Later I will move on to A17
--- End quote ---
Ok A7 from the interconnect diagrams refers to circuit diagram numbers 7,9,11,12 as seen on the bottom right of the manual schematics , ie multiple schematics make up the overall A7.
A17 is circuit diagram 3.
Does the 48V rail work ok with an appropriate resistive load ?.
Be mindful that there is a number of custom HP parts (eg U2 ) and you should use proper handling procedures when out of circuit. Hopefully none of those are broken. BTW that IC U2 is running off the 5V rail.
Use the interconnect diagrams to find which schematic sections use the 48V rail and work through likely failures.
Remove A17 and check the 48V rail (possible A1 output amp failure which uses 48V).
jeno:
I think I managed to repair A1 and A17 (not 100% sure) now all my voltages look Ok when the LVPS is connected to the rest of the components, I also managed to get somthing in the screen, it's all green, none of the buttons doind anything, On the vertical preamplifier I measure 9.23volts at TP1, What can be now the problem?
electronix27:
Hi everyone, bit late to the party here. Just picked up an HP 1740A, and enjoyed reading this post. There are a few circuit issues but the CRT is in great condition. Figured I’d start with a good cleaning. Bit stumped on how to remove the sweep dial from the shaft. Appears to be a small C clip on the notched shaft or maybe something I’m missing. Appreciate your help.
Much Thanks
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version