HP 1741A oscilloscope - restoration project

[AlienRelics]

Thanks!

I did find a free source for a PDF of the service manual.

[techie1234]

Keeping this thread alive...I'm working on a 1743A and am having problems with TIME/DIV controls.  The main control won't rotate more than a couple of positions CW or CCW - sounds like it might be a bent contact in the rotary switch or perhaps some hardened grease.  Also the delay TIME/DIV knob cracked off, but at least the shaft rotates easily by hand.  And those grub screws in the knobs are a pain - wish they would have milled some flat surfaces into the shaft so the set screws could mate flush.  Seems like this is a weak point on these scopes.  Will be having a closer look inside...

My main question is: is there a version of the 1743A manual that has as much detailed repair information as the 1740A one?  The 1743A manual on the Agilent site:

http://cp.literature.agilent.com/litweb/pdf/01743-90905.pdf

has a BoM and exploded diagrams but not a schematic, repair procedures, etc.

Also, are there any recommendations on who sells various parts (like the aforementioned cracked delay TIME/DIV knob) for the 174x series?

[tautech]

Keeping this thread alive...I'm working on a 1743A and am having problems with TIME/DIV controls.  The main control won't rotate more than a couple of positions CW or CCW - sounds like it might be a bent contact in the rotary switch or perhaps some hardened grease.  Also the delay TIME/DIV knob cracked off, but at least the shaft rotates easily by hand.  And those grub screws in the knobs are a pain - wish they would have milled some flat surfaces into the shaft so the set screws could mate flush.  Seems like this is a weak point on these scopes.  Will be having a closer look inside...

My main question is: is there a version of the 1743A manual that has as much detailed repair information as the 1740A one?  The 1743A manual on the Agilent site:

http://cp.literature.agilent.com/litweb/pdf/01743-90905.pdf

has a BoM and exploded diagrams but not a schematic, repair procedures, etc.

Also, are there any recommendations on who sells various parts (like the aforementioned cracked delay TIME/DIV knob) for the 174x series?

IIRC a 1740 I had at one time did the same and I'm pretty sure it's a result of incorrect reassembly, at least it was in mine....I'd had it apart. 
The timebase shaft goes through a # of selector wafers on a # of plugin PCB's and if the wafers aren't in the correct positions you end up "hamstrung" as you describe. Some careful fiddling should sort it out. One wafer might be 180 out.
Thinking back.....the timebase shaft is withdrawn from the front panel, knob and all after the shaft retaining collars are loosened on the shaft, each retaining collar hex grub screw retained IIRC.

[techie1234]

IIRC a 1740 I had at one time did the same and I'm pretty sure it's a result of incorrect reassembly, at least it was in mine....I'd had it apart. 

I'll second that, having had similar experiences on my hp1740.
It is surprisingly difficult to get both knobs, both shafts and both rotors in the right position. It is even worse if, like me, you had also moved the knobs on the shaft in order to add a more visible legend to the timebase control.

Turned out you both were pretty close - the boards appear to have been knocked around a bit at some point.  The side of the boards closest to the case were all about 10 degrees flexed towards the back of the case, relative to the side of the chassis. As such, the middle board (for the main TIME/DEV) was askew relative to where it mated with the shaft.  A careful bit of forward pressure and "pop" - all three boards returned to perpendicular, unjamming the main TIME/DIV shaft.  All is now good. They should really have had slots on the case side for each board to slip into so they weren't just held in place by the one edge connector.  Now to find those knobs...

[atlacamani]

Hello guys .
sorry for my english, i use the google translator to communicate with you.
A friend gave me a disassembled oscilloscope hp1741a. I want to collect it
but I do not know where to connect some wires. Help please. Look at the photo please.

[atlacamani]

general picture

[lowimpedance]

Here are some pictures of my HP1741 showing the wire locations.
If you need any further pictures now's the time to ask before I put the covers back on !.
BTW when needing to service any module or switch assembly, make sure to take many photos before anything is undone !. (I'm sure you already have that in mind now  ).

[lowimpedance]

last set !.

[peterpan]

Listen to my friend!
HP makes your job easier: there is a number for each wire connection, eg. 956. Equal to the color of the matching wire according to the resistance color scale: 9white, 5green, 6blue equal to white wire with blue and green stripe. I tak dalee ...
Hi. PP

[atlacamani]

last set !.

lowimpedance, you really help me, sorry for long silence, it was not my  fault.. My oscilloscope  waiting  me for a year)))
only one wire left:

[atlacamani]

Listen to my friend!
HP makes your job easier: there is a number for each wire connection, eg. 956. Equal to the color of the matching wire according to the resistance color scale: 9white, 5green, 6blue equal to white wire with blue and green stripe. I tak dalee ...
Hi. PP

thank you friend))

[jeno]

Hi, I just got a HP 1741a oscilloscope, and the power supply is bad, none of the voltages match their rating, i replaced two burnt resistors, one of the power tranzistors and some capacitors and still nothing, anyone help?

[lowimpedance]

What voltage is coming out of the bridge rectifiers ?, they do have a hard life so check for dry joints etc .
Also the transistor connectors for the pass transistors on the rear panel maybe not making good contact.
Just tossing a few ideas, perhaps a few good pictures of your power supply PCB if you think it useful unless its pristine .
One other point to note is odd symptoms can also be caused by resistors that have drifted high upsetting critical bias points in the DC coupled circuits, both power and signal paths.

[jeno]

After replacing the bridge rectifier for the +15v rail bridge rectifier, all of the filter caps after the bridges, I have all good voltages at the diode bridges, +5v, +15v, -100v rails are fine but the +48v is reading 26volt and the +120v is at 188v, at the +48 and the +120v the 2w resistors were totally burned i replaced them but still not ok, for the -15v my regulator ic is bad, ill try to put an LM723 for that. But I noticed that the horizontal output board is also has some burnt parts, but I dont have the schematic for that, even for the power supply I paused Dave's video when he showing the schematic.

[jeno]

I also need to get somehow the values of theese components, or the horizontal output schematic

[lowimpedance]

Thats quite some bbq-ing there  , I assume its now clean though !. The manual on this site is ok and has the Horizontal op circuit.

https://elektrotanya.com       ,scroll down for the search window. Read the supply circuit descriptions etc.

Given the damage you really need to isolate the LV power supply from the rest of the unit to fully debug it first as the 120 and 48V rails are
referenced to other supplies and if those are not fully functional things will go bad quickly. So best to trouble shoot in isolation then when working
look for other damage (beyond the horizontal OP PCB as well).  So just to confirm you only get 26V across C5 and 188V across C3 ?. Does that change when
the supply PCB is isolated from the res of the instrument ?. BTW be mindful of the voltages your playing with in the 1741 and follow best safe practices.

[jeno]

Thank you very very mutch, this manual is very useful, i was searching it for days but couldnt find it, whithout the manual it was very hard to understand the working principle, now I vill start measuring all the resistors and all components one by one, I really want to get this boy up and running. Thank you very mutch.

[jeno]

Can someone recomend me some good modern day replacement tranzistors for the A11 board? Only one of the tranzistors survived there, and I cant find any information for those Iwas thinking about BD439,Bc547 and their PNP brothers but Im not sure that those will be fine.

[jeno]

Now my three main supplyes are good, I had to make some little adapters for the LM723 from DIL14 to TO100package, I couldn't get TO100ones, But my +120v and +48v rails are busted, I'm measuring +186volts at the +120v and 26volts at TP5 across C5 I have 78volts, but betwwen the negative side of C5 and GND I'm measuring -52 volts. Across C3 I have 186volt, and betwwen the negative side of c3 and GND I'm measuring -7.5volts. These measurments does not change id I disconnect the power tranies, the power supply is disconected from the rest of the circuits. All the transistors seem fine, what can cause this problem?

[jeno]

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.

[lowimpedance]

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.

 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]

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

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