PM3055 Phillips Scope fault - Page 1
Forum section: electronics / testgear

author: sherb_j
author_rank: Newbie
timestamp: April 09, 2014, 12:13:36 pm
content: Hi All,Nice to be on this forum.I'm working on a PM3055 50MHz scope (got the manuals). Have replaced a burned out X2 cap and scope has come alive.But ... all appears well except the A channel Y pos deflection doesn't work ( B channel is fine). If I apply a waveform(5v p to p) to the A input thenI can see the top of the wave peaks at bottom of screen when I drop the scope to the millivolt range, also if I kick in the Trig View then I see the whole wave form, centre screen but can't move it vertically. Any ideas as where to start looking would be much appreciated.Got a couple of sheered pot spindles also. As they appear hard to come by, I've cut a slot in them so can adjust with a screwdriver. Look forward to hearing from you.John.

author: tautech
author_rank: Super Contributor
timestamp: April 09, 2014, 07:45:51 pm
content: Just offer a simple but distinct waveform (square-wave, even probe cal output) to A input and follow the signal path with another scope.

author: Shock
author_rank: Super Contributor
timestamp: April 09, 2014, 11:40:07 pm
content: Reconnect and clean all the cables connections as well that's a common problem.I would check the back of that control board and see if it has intermittent solder joints.I couldn't find anything suitable as a pot replacements. They aren't rare at all, they are just sitting on other scopes.I brought a damaged spare to repair the broken pots on mine just a couple of days ago.

author: sherb_j
author_rank: Newbie
timestamp: April 10, 2014, 07:24:28 am
content: Ok, guys.Many thanks for advice. 'Fraid I can't scope the scope as don't have access to another one but will look for dry joints etc.Thanks again.John.

author: tautech
author_rank: Super Contributor
timestamp: April 10, 2014, 07:57:18 am
content: Often the manuals have DC test points on the schematic. Usually you have to set the scope in a specified way for the DC measurements. RTFMYou might strike it lucky, but when one owns an old scope you normally need another to fault find when it dies.

author: Shock
author_rank: Super Contributor
timestamp: April 10, 2014, 10:41:33 am
content: You can get both manuals here.

author: oldway
author_rank: Super Contributor
timestamp: April 10, 2014, 11:00:01 am
content: It seems to be a defective input fet, (BF410C) V1003, or V1006, or V1011, or V1016.

author: sherb_j
author_rank: Newbie
timestamp: April 11, 2014, 09:35:35 am
content: Thanks to all for your responses.I'll have a look at the fets and thanks for offer of manuals.Much appreciated everyone.John.

author: (*steve*)
author_rank: Regular Contributor
timestamp: April 13, 2014, 12:13:48 am
content: Hi John,I have one of these units with a similar fault, although my 0.22uF cap did a little more damage before it finally gave up.This cap(?) here (the ceramic(?) one below and to the left of the 0.22uF X2 cap:Looks like this on mine:If you want more details, I have posted more stuff herehttp://www.electronicspoint.com/threads/pm3055-oscilloscope-psu-failure-dont-leave-your-scope-turned-on.268181/Basically, I want to know what that component is because it doesn't appear on the overlay in the service manual. I'm going to try to clean it up today to see if I can decipher any writing, but I'm not hopeful.By the way, you got off lightly with the 0.22uF cap (maybe not on the other faults). One of my 68uF capacitors vented its contents and the 0.22uF cap had a rather more pyrotechnic failure. But I'm hopeful of a successful repair.Whilst mine is naked on the bench... If you need any measurements made on my scope to compare against yours (that can be made without a working power supply), please ask and I'll try to oblige.

author: (*steve*)
author_rank: Regular Contributor
timestamp: April 13, 2014, 02:05:36 am
content: I now think it may be a 1.5nF ceramic, but I'm not sure of the voltage rating.

author: Shock
author_rank: Super Contributor
timestamp: April 13, 2014, 05:27:28 am
content: I think it's 105c as well from your photo. Looks like they moved it on the board.My photo is from a different model but I checked 3 models including the PM3055 and all the service manuals had the same part for C6005.You could confirm anyway by properly following the PCB traces to C6007.

author: (*steve*)
author_rank: Regular Contributor
timestamp: April 13, 2014, 05:48:26 am
content: *Thanks*I was about to order some 1.5nF 2kV caps -- I'll try to find 3kV ones -- or go back to my fallback position of a 2.2nF 3kV cap.It is interesting to see how the placement of these caps changes in various revisions of the boards. I also note that the 4 10k resistors I have are higher tolerance than yours but there seems to be no real purpose for this.The yellow cap behind that is C6017 (2kV 1n5 5%) on my board, and C6005 is what we have identified as 3kV 1n5.Yes, look like 125C rated. I have the choice between:* Lower voltage (125C, 2kV, 1.5nF)* Lower capacitance (125V, 3kV, 1nF)* Lower temperature/higher capacitance (85C 3kV 2.2nF)None make me happy.

author: sherb_j
author_rank: Newbie
timestamp: April 13, 2014, 12:46:16 pm
content: Hello Steve,Thanks for reply. My scope also has the black mystery component (on ceramic stand offs). It's directly behind the yellow plastic 2 x 10 mH choke encapsulation.It seems to look ok (not fried or anything). Yes, there seems to be some mods to the psu layout not as the manual. Also I can't find the glass fuses !! - could you tell me where they are on your box, please ? If I can get this scope fully functioning, it will be a result as someone gave it to me after rescuing it from a skip. It did put up smoke when we plugged it in at work (the X2 cap incinerating) - would have got us both fired had it set of the sprinklers !! We blamed the smell on another colleague's breakfast toast !Nice pics, SteveStill scratching my head, here ! - John.

author: Shock
author_rank: Super Contributor
timestamp: April 13, 2014, 01:14:09 pm
content: If you mean the mains fuses if you look at the operation manual it should point to the fuse socket on the outside rear of the scope just above the line in (power socket).250v 1.6A delayed action (slow blow).

author: (*steve*)
author_rank: Regular Contributor
timestamp: April 13, 2014, 09:20:51 pm
content: Yeah, as per shock. Pull out the power liad then the upper portion of the IEC socket pulls out revealing a holder with the fuse and a spare.I had to use a small screwdriver to get mine to come out, it was a little stiff. I expect it hadn't been opened since new.Mine doesn't have that common mode choke. I suspect the board had many revisions and the service manual fewer...Speaking of the service manual. It has a nasty habit of making things sound a lot easier than they are. Those damn clips for the board for example!

author: sherb_j
author_rank: Newbie
timestamp: April 17, 2014, 04:11:10 pm
content: Ah, right. Thanks for advice on finding fuses (just in case they get blown !!).I want to get at the attenuator board next, to check the fets in there, (as previously advised). Doesn't look easy, as it's under a metal plate.Has anyone taken one of these out ?Cheers,John.

author: (*steve*)
author_rank: Regular Contributor
timestamp: April 24, 2014, 06:17:40 am
content: Thanks for the assistance.My scope is not happy and apparently healthy. I get to pass up on SWMBO's offer of letting me go out and buy a new one.Oh and thanks also to RS's free shipping and some 4 cent fuses (http://australia.rs-online.com/web/p/cartridge-fuses/7833305/) that make you less concerned about buying 10 at once.

author: sherb_j
author_rank: Newbie
timestamp: June 29, 2014, 01:29:25 am
content: Sorry to be a bore but, the two main electrolytics on the power supply of my PM 3055 scope have dimples (dents) as though they could have imploded. The beast powers up ok (still can't get the A channel to work). Do I need to replace these two caps ??Regards, John.

author: Shock
author_rank: Super Contributor
timestamp: June 29, 2014, 02:28:58 am
content: Yes if your intending to keep it replace the X2 as well. Those are the 2 most common failures.