Philips PM3055 scope

[Specmaster]

I have a chance of getting a PM3055 scope as a non runner, as far as I know, the LED's light up but nothing on the screen and although I already have 2 scopes, both Rapid Electronics (7020A 20Mhz and 7025 25Mhz) dual channels, rebadged Pintechs I think, I was rather keen to look at fixing up the Philips as well if its viable.

Does any member have any experience of what the likely problem is going to be, does this model have any particular vices? I have been scouring this forum and have come across a number of threads regarding this machine.

One in particular where jancumps posted a nice screen shot of this back in August 2014 hat showed no fewer then 8 traces on the screen where he explained that the upper 4 were from the on board memory and the lower four were in real time? This has me scratching my head just as to how was this possible from a dual channel scope or is it a special party piece of this scope and I'm missing something?

I have downloaded some form of a manual for this scope but not read it as yet, still gathering as much information as I can about it.

Many thanks in advance for any useful tips and comments put forward.

[jancumps]

It's a 4 channel scope. The bnc connectors for 3 and 4 are on the backside, you can change their y position wih trimpots that are reacheable via holes on the left side. Channels 3 and 4 only work in digital mode.

My 8 beams show 4 signals captured in memory and 4 live signals.

[Specmaster]

Thanks for the speedy reply, that makes sense now. Di I then also take it that say channel 3 would share the same Volt/Div switch as channel 1 and that channel 4 and 2 share the respective switch as well?

My current scopes are very basic ones so I have not across rear mounted sockets before.

I'm learning something new everyday here, thanks.
 

[jancumps]

Channel 3 and 4 have two predefined volt/div settings. You switch by connecting the probe to a different BNC at the back.

The switches on the front pannel are not shared.

[george.b]

Wait, what?

The PM3055 is a 2-channel analog scope. Or rather, "2+1" channels, as it can also display the trigger signal. It can show 6 traces: the 2+1 channels, plus those same channels in the second timebase.
I looked for jancumps' screenshot - that's a PM3305, not a PM3055:



This is a PM3055, using the DTB to show 4 traces:

[jancumps]

you are right. I have dixlescia

[Specmaster]

Thanks George B, and that makes two of us then jancumbs, because I did start the thread off with a question about PM3055 and then dragged you into it erroneously because you were talking about a PM3305. My only defense was that I did post late in the day when I should have been in bed I guess, cheers everyone for your kind inputs.

Any more info on the possible causes of a PM3055 to switch on but not display any traces would be welcome before I make a decision to purchase a scope that could perhaps turn out to be:-
A/ Uneconomic to repair or B/ getting a bit long in the tooth so major problems may just round the corner after I repair it and that I may be better off sticking with what I already have or looking for another newer model, if so what would you suggest I look for?

I went initially for the 2 Rapid scopes as they were almost brand new and are still on sale new today, so I figured that as many other companies badge these scopes, that they must be reasonable enough, albeit a bit basic and of a low bandwidth.   

[tautech]

Thanks George B, and that makes two of us then jancumbs, because I did start the thread off with a question about PM3055 and then dragged you into it erroneously because you were talking about a PM3305. My only defense was that I did post late in the day when I should have been in bed I guess, cheers everyone for your kind inputs.

Any more info on the possible causes of a PM3055 to switch on but not display any traces would be welcome before I make a decision to purchase a scope that could perhaps turn out to be:-
A/ Uneconomic to repair or B/ getting a bit long in the tooth so major problems may just round the corner after I repair it and that I may be better off sticking with what I already have or looking for another newer model, if so what would you suggest I look for?

I went initially for the 2 Rapid scopes as they were almost brand new and are still on sale new today, so I figured that as many other companies badge these scopes, that they must be reasonable enough, albeit a bit basic and of a low bandwidth.

Much depends on your knowledge, ability and tools on hand to undertake CRO repairs.
If a service manual or at the very least a User manual WITH schematics is not available then DON'T touch it.

If the display is not working it need be very cheap or free and if you have the skills sometimes these can be a bargain. Many CRO repairs are not trivial due to the high voltages present and need for equipment that can handle such. Generally the HV circuitry is the most under stress, that's just how CRO's are.
I've said many times and now another member has as his signature: If you own a CRO you'll need another to keep it going. Sad but true.

[george.b]

The service manual for the PM3055 is readily available, but I would be wary of getting any cathode ray tube oscilloscope that comes on and doesn't display a trace.
IMO, the most likely causes, in decreasing order of likelihood, are: a faulty flyback transformer, some fault in the FBT drive circuitry, some fault in the supply rail for the HV section, or some other fault somewhere else that's preventing the display from coming up.
In case it's a toast FBT, it's pretty much like tautech said, you'll need to cannibalize another PM3055 (or a very similar unit, like the PM3050) to repair it.

[Specmaster]

Many thanks everyone for their input, in the end I snapped up an Iwatsu SS-5710 4 trace scope that was working but was thought to require calibration, subsequent careful cleaning of the controls with WD-40 contact cleaner soon sorted those out, all I had to in the end was to replace the power on LED as the old one was not working. Overall the unit was clean but showed signs that it had been neglected for a while. Scrubbed up a real treat.

Like the 3305, the inputs for 3 & 4 are a bit restrictive as they have fixed input ranges of .1v and 1v but they add that extra degree of functionality if required.

[george.b]

Nice, congratulations on the new scope! Always nice when it's an easy fix.
I'm all for fixing and extending the useful life of equipment, but that PM3055 sounded like trouble.