Author Topic: PING Louis Rossmann, you're needed in surgery! Repairing an Agilent DSO8104A  (Read 5019 times)

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Offline vze1lryy

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Re: PING Louis Rossmann, you're needed in surgery! Repairing an Agilent DSO8104A
« Reply #25 on: September 29, 2017, 04:55:03 am »
Why on earth is this a public post?


marketing

We honestly don't advertise or solicit this stuff since we don't do it... for the record, if someone mistakes any of my posts for marketing odd jobs, and you have something that is not a liquid damaged macbook.. from the horse's mouth here, you should not send it. If we are busy with "regular" repairs then the odd stuff people drop off(refrigerator PCBs/oscilloscopes/other weird stuff) winds up at the bottom of the pile... and steve will always kick my ass for taking in some refridgerator PCB/custom PCB/odd audio interface since we can't test it. usually flux is cleaned off in the ultrasonic but a Crest CP500D we bought for laptop boards is never going to fit this. No video since too busy by far over the past month to do any regular repair videos. I didn't do this one so not sure what it could be, I'll ask jason how he did it and take a look when it comes back... odd that it didn't work.

I'll take a 2nd look once it comes in. I'm sorry to hear it didn't work.
Louis Rossmann
Component level motherboard repair technician.
 
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Offline Jwalling

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Re: PING Louis Rossmann, you're needed in surgery! Repairing an Agilent DSO8104A
« Reply #26 on: September 29, 2017, 03:22:34 pm »
(Whining snipped)


We honestly don't advertise or solicit this stuff since we don't do it... for the record, if someone mistakes any of my posts for marketing odd jobs, and you have something that is not a liquid damaged macbook.. from the horse's mouth here, you should not send it. If we are busy with "regular" repairs then the odd stuff people drop off(refrigerator PCBs/oscilloscopes/other weird stuff) winds up at the bottom of the pile... and steve will always kick my ass for taking in some refridgerator PCB/custom PCB/odd audio interface since we can't test it. usually flux is cleaned off in the ultrasonic but a Crest CP500D we bought for laptop boards is never going to fit this. No video since too busy by far over the past month to do any regular repair videos. I didn't do this one so not sure what it could be, I'll ask jason how he did it and take a look when it comes back... odd that it didn't work.

I'll take a 2nd look once it comes in. I'm sorry to hear it didn't work.

Hi Louis,
Never-mind the whiners that have nothing to worthwhile to contribute.

I greatly appreciate the work you've done for me on that TDS694C some months back (and the one you now have in your possession), as well as on this DSO board repair project as well. Sometimes things go wrong; believe me I understand that! It doesn't help at all that you don't have any way to test after doing the re-work...

Anyway, I hope that you'll still be open to doing future repairs for me, but I understand this may be a bit out of your comfort zone. If not, then that's OK as well.

I'm going to try to reflow the pin/pad a bit and see if the short goes away, hopefully today, but if not, then tomorrow
Thanks.

Jay

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Offline Jwalling

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Well, I was unable to remove the short by reflowing the pad or using solder wick. So I attempted to break the connection by carving out the conductive material with an x-acto knife on the chip itself in the vertical half circle that runs down the edge of the chip. This was successful, so I cut the 1cm etch that runs to a via and put a wire from the via to the top of the chip where the silver conductive material goes under the top cap of the chip. This is where things went wrong. That silver material did not like being soldered - it sort of just disappeared.  |O

In hindsight, I should have used the x-acto knife to cut away the connection where the half circle solder point meets the PCB itself, then run the wire from the half circle to the via. Live and learn. :(

So the chip will need to be replaced again with another donor chip.

During all this screwing around, I also noticed the Teledyne RF relay was cooked. Measuring resistance at the BNC in 50Ohm mode at some vertical amplitude settings, the impedance was 285 Ohms. So it looks like someone overloaded the input when the scope was in 50 Ohm mode. That's replaced and all is well there now.
Jay

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Online TheSteve

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Ouch - I believe anytime you solder anything to a trace that is on ceramic you need to use silver solder.
VE7FM
 

Offline wraper

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Ouch - I believe anytime you solder anything to a trace that is on ceramic you need to use silver solder.
FYI SMT resistors and capacitors are made from ceramic. Special leaded solder with added silver is thing of the distant past. Pads on remotely modern parts have nickel barrier on top of the silver protecting it from dissolving. It rather sounds that metallization was torn off by mechanic impact, and when soldered, was just washed away with liquid solder.
 

Online PA0PBZ

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Since it is unusable as it is now, try to decap it? If it doesn't work out at least you'd get some pretty pictures :)
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Offline Jwalling

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Since it is unusable as it is now, try to decap it? If it doesn't work out at least you'd get some pretty pictures :)

I probably will after it's replaced; I won't attempt to repair or re-use it, though. I've requested that he return the damaged chip with the boards when he send them back. Luckily I have more spares to replace it with!
Jay

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Offline Jwalling

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Update. Board is back after having the chip replaced again. Still failing cal. but somewhat normal waveforms can now be seen! I now believe that the pre-amp is operating correctly (Thanks Louis!). There's many more "PASSED" tests in the debug log. Before and after attached.

I now have a high impedance fault to figure out... Amplitude is way too high, and some distortion on top and bottom of square wave. Whoever blew this scope's input really meant business!

EDIT: Since the blowout occurred in 50 Ohm mode, I'm wondering if the scope sensed the overload and switched over automatically to 1M, thereby blowing something the 1M path as well? The Tek TDS700X input hybrids do this...
« Last Edit: October 12, 2017, 11:36:16 am by Jwalling »
Jay

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Offline Jwalling

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Obligatory chip porn as promised. This is the one I mucked up trying to remove the GND short and adding a wire.

The ceramic cap is bonded to the substrate using a material very similar to RTV. Must be a high temp version as no discoloration or burning is noted. It was a breeze to de-cap.
« Last Edit: October 11, 2017, 05:18:44 pm by Jwalling »
Jay

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Offline Jwalling

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One of these days, I'd love to get a microscope with the ability to take hi-res pictures. Not in the budget now...

If anyone in the US has a setup like that and wants to take some good pictures for us, I'll mail the chip for free!
Jay

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Offline Samogon

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I can try Amscope x40 with 5mp camera
 

Offline Armadillo

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Something like this would be at ~X50 or X70, can't remember.
Was trying to get good depth of field but my lighting was at the max.
 

Offline AF6LJ

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Good deal Jay, sounds like you are well on the way to having that scope back on the road.   :-+ :-+
Sue AF6LJ
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Offline Jwalling

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I can try Amscope x40 with 5mp camera

PM sent. Thanks.
Jay

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Offline Jwalling

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Still working on the DSO.

In other news, Louis has performed another successful trigger chip swap on a TDS694C for me.  :-+
This one failed to trigger on CH1 and CH2 with two obviously burnt chips in U1823 and U1813. While U1833 wasn't obviously blown, it had a very slight brownish color to it, so I didn't trust it. The board was repaired by using the spare chip from the previous repair back in April, and placed in U1823.

EDIT: wrong picture posted.
Jay

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Offline AF6LJ

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 :-+ :-+
Good deal.
Sue AF6LJ
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Offline Samogon

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Jay, got your chip today
Here are some snapshots from may Amscope 45 with barlow lense x2 and 5MP camera.
I have articulating arm which is extremely shaky on x90 magnification. Hard to get focus
 
« Last Edit: October 21, 2017, 06:02:58 am by Samogon »
 
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Offline AF6LJ

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Nice shots, thanks for posting them.  :-+
Sue AF6LJ
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