oscilloscope for troubleshooting mobile phones

[poseido]

Hello;

I've been browsing the forum for a while and I can not find an straight answer to this question:

what specifications a oscilloscope must have to be used in mobile phone repair/troubleshooting ? I'm starting to think on learning the job, and I'd like to purchase some equipment... but I do not want to purchase an expensive (and useless)piece of hardware because I do not know exactly what to get.

thanks in advance!

(the idea is to troubleshoot not signal/aerial issues but pcb and components problems in 2 3 and 4g mobile phones)

[Alex Eisenhut]

Hello;

I've been browsing the forum for a while and I can not find an straight answer to this question:

what specifications a oscilloscope must have to be used in mobile phone repair/troubleshooting ? I'm starting to think on learning the job, and I'd like to purchase some equipment... but I do not want to purchase an expensive (and useless)piece of hardware because I do not know exactly what to get.

thanks in advance!

(the idea is to troubleshoot not signal/aerial issues but pcb and components problems in 2 3 and 4g mobile phones)

What mobile phone can be troubleshooted with a scope? The biggest concerns are
1) What are you probing without a schematic? These phones are fantastically integrated and complex embedded systems with RF modules.
2) How can you probe? Have you seen a modern phone? You're lucky if you even *have* traces on the outside anymore! And if you have test points, you need to know what they are.
3) Your usual scope probe would be like trying to perform brain surgery with a shovel.
4) Then what? How can you desolder and resolder SMT parts packed super tight on a HDI PCB and under metal shields?

Most problems I've seen with phones are cracked screens, dropped cases, defective switches, bad batteries, software issues. You just need a good set of screwdrivers, suction cups, soldering iron, multimeter. That's it.

[aveekbh]

Hello poseido,

As Alex mentioned, this kind of repair would be extremely difficult to do. The norm these days is to use BGA-type packages (like the WTR1605 in Alex's picture), which cannot really be soldered by hand.

I believe the repair approach these days is to replace the failed module, which just requires some (or quite a lot of) careful assembly.

If you are really serious about this, I would imagine a 'scope with 100-500 MHz bandwidth would be sufficient - but that can be quite expensive. Anyway, there's not much you can do with the RF stuff with a scope - for that you need a spectrum analyzer.

Hope that helps 

[poseido]

Hi

thanks for the quick replies;

to Alex Eisenhut

1) I do have the schematics of the phones I'll try to repair
2) I do have testpoints on the phones, and know what they are (as said, I have factory the schematics)
3) ummm.. ok
4) maybe a SMT level repair is not the aim, just basic checks on the pcb's (is the current ok, etc)

of course it will not be a "factory quality department level repair"


to: aveekbh

I'm not planning to check RF, just basics on the pcb's

[AG6QR]

I'd start with a good multimeter and a good set of small, sharp probes intended for SMD work.  Fluke TL910 or Pomona 6341 probes are basically the same thing with different branding, and they're good for working on crowded PCBs filled with tiny SMD components.

There are many multimeter threads -- I don't have too much to add except to say that you shouldn't try to go too cheap with what will be your most used electronic diagnostic tool.  Get a decent meter.

As for a scope, until you know what it is you want to measure with it, I'd be tempted to postpone the purchase.  When you DO know what you want to measure, that will give you an idea of your bandwidth requirements, the number of channels you'll need, and any kind of special features to look for.  Personally, I don't know of many reasons a repair technician would need to use a scope on a phone very often, but then I don't have a lot of experience in that area.

[Alex Eisenhut]

Hi

thanks for the quick replies;

to Alex Eisenhut

1) I do have the schematics of the phones I'll try to repair
2) I do have testpoints on the phones, and know what they are (as said, I have factory the schematics)
3) ummm.. ok
4) maybe a SMT level repair is not the aim, just basic checks on the pcb's (is the current ok, etc)

of course it will not be a "factory quality department level repair"


to: aveekbh

I'm not planning to check RF, just basics on the pcb's

Factory schematics, as in a service manual? They usually tell you what equipment you need.

And as for 3, look at the size of a scope probe tip, look at the size of the components.

The only scope probes I've seen that are meant to work with 0201-ish parts are the ones that come with DCAs. They need to be soldered in.

[poseido]

AG6QR, advice well noted, first a good pair of sharp probes and a good multimeter
Alex Eisenhut, many thanks, I'll check those manuals as soon as I get them

thanks guys, so far I have in my mind not to purchase the oscilloscope.

[Alex Eisenhut]

AG6QR, advice well noted, first a good pair of sharp probes and a good multimeter
Alex Eisenhut, many thanks, I'll check those manuals as soon as I get them

thanks guys, so far I have in my mind not to purchase the oscilloscope.

Well, not for phone repair, no.
If you really do actually have the information about the test points and what they do, I'd suspect a logic analyzer is the tool you want. Maybe even a jtag pod.

[aveekbh]

AG6QR, advice well noted, first a good pair of sharp probes and a good multimeter

At work, I use the Agilent Keysight 34138A (they come as standard accessories with their high-precision bench multimeters). They have these really sharp probe extenders (like needles) that can actually be used even with 0201 components (with a really steady hand).

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