HP 1741A oscilloscope - restoration project

[calmtron]

I have a 1742A that have/had the same problem with the grub screws. The solution that worked for me was to use high quality hex keys, not-so-gentle tapping and lots of patience. Unfortunately i used cheap hex keys (one hung low ones) first and managed to strip the heads of the screws on one of the the timebase knobs.

I don't think there's any locking compound on the screws, it just looked like a bad case of galling / oxidation. Heating the screw seems like a good idea to try.

[tautech]

The timebase shaft goes through 2 plug-in PCB's and have grub screwed shaft retaining collars.
Form memory the manual describes a method to remove these PCB's that entails removing that shaft, and that will allow you to clean the dials.

[tggzzz]

The timebase shaft goes through 2 plug-in PCB's and have grub screwed shaft retaining collars.
Form memory the manual describes a method to remove these PCB's that entails removing that shaft, and that will allow you to clean the dials.

That's the mechanism, but the grub screws holding the knob onto the shaft is the problem - the legend is "between" the two knobs and shielded/protected by transparent plastic.

[tggzzz]

Thanks for all the suggestions. The problem has now been circumvented...

The original 0.050" grub screws are still as immovable as ever, despite gentle thumping/heating, WD40, gentle force. I didn't want to apply too much of any of those since the knobs were functional and I was afraid I would melt/break adjacent plastic parts of the knobs.

In the end the other two grub 1/16" screws on the delayed timebase were persuaded to turn, which allowed me to disassemble the knob and insert a replacement legend. Sure the font and colour aren't right, but at least I can read them!

[SAUL BRITTO]

Tekfan I need your help! I need to know if the focus unit of 1740A is the same as the 1741A.
I bought an unit of 1741A that the seller said me that, the problem was in the focus unit and I do have a dead one 1740A.

[AlienRelics]

Wow, this is a long-lived thread.

I was just given two 1741A 'scopes for free. I have no idea what is wrong with them, other than that they do not work. I'll be posting pictures and progress.

[tggzzz]

Wow, this is a long-lived thread.

I was just given two 1741A 'scopes for free. I have no idea what is wrong with them, other than that they do not work. I'll be posting pictures and progress.

If you don't have one and need to open it the 1741, strongly consider getting the service manual from http://artekmanuals.com/manuals/hp-manuals/

[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?

[tggzzz]

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

Sphere (Canada), QService (Greece, US), ebay.

It is useful to have exact part numbers, which you can find in the service manual.

[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.

[tggzzz]

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.

[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...

[tggzzz]

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...

Good stuff!

For future reference, my A timebase was faulty and I traced it to two problems. A faulty 100uF electrolytic was easy, but some PCB tracks had been abraded and needed replacing.

The tracks in question are inside the rotary PCB switch. To access them, remove the board, slide off the spring clip so the two black switch halves can be removed from the PCB, but don't drop the internal spring contacts!. The edges of those black halves rub against the PCB at their periphery, and eventually sever the PCB track. The track(s) can be replaced with fine wire and careful soldering - try to avoid getting solder on the gold contacts.

[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