PING Louis Rossmann, you're needed in surgery! Repairing an Agilent DSO8104A - Page 1
Forum section: electronics / repair

author: Jwalling
author_rank: Unknown
timestamp: August 16, 2017, 03:59:31 pm
content: I've got a customers DSO8104A on my bench that won't self calibrate. CH1 has a bad/blown pre-amp - it's input impedance from the attenuator is way too low (The calibration routine doesn't even detect that the coax cable is connected from CH1 to the AUX OUT connector, and "common" calibration fails). The cal log is attached.Luckily I have a few scrap 54831B/32B acquisition boards around as they use the exact same preamp. Once again though, I don't have the needed equipment or expertise to do the repair as there's a large GND pad underneath the chip. The chip is entirely made of ceramic; whether this requires more delicate handling and heating to keep it from cracking is unknown. It looks like the "cap" of the chip is bonded to the bottom ceramic plate where the die lies; I'm hoping the cap doesn't fall off as I have no idea what material holds it together. Hopefully not glue!I'm going to have Louis Rossmann do the repair work again like he did in this thread:https://www.eevblog.com/forum/repair/looking-for-someone-who-can-replaceswap-tek-tds694c-trigger-chips-for-$/msg1186021/#msg1186021Does he read this forum? Let's find out!Pictures of the good chip on the scrap donor board, and the bad chip on the board to be repaired are attached as well.

author: vze1lryy
author_rank: Regular Contributor
timestamp: August 17, 2017, 04:41:01 pm
content: Sure. Might use the zm-r6200 if more precise heating is required for the ceramic. Send it in.

author: Jwalling
author_rank: Unknown
timestamp: August 17, 2017, 04:50:58 pm
content: Excellent. Will get it shipped out to you tomorrow. Thanks!

author: tooki
author_rank: Super Contributor
timestamp: August 17, 2017, 08:44:21 pm
content: Quote from: Jwalling on August 16, 2017, 03:59:31 pmWhy on earth is this a public post? You could have sent him a PM, or an email, or called his office... nothing about this needed to be public.

author: Toasty
author_rank: Regular Contributor
timestamp: August 17, 2017, 08:55:08 pm
content: Because someone else might have this problem and need assistance. Just a thought.T

author: KE5FX
author_rank: Super Contributor
timestamp: August 17, 2017, 08:56:45 pm
content: Quote from: tooki on August 17, 2017, 08:44:21 pmMuch the same could be said of your post.One difference is that the result of Louis's repair attempt will make for an interesting follow-up.

author: RGB255_0_0
author_rank: Frequent Contributor
timestamp: August 17, 2017, 09:01:58 pm
content: Would be cool if he live streams itAlso would be interesting to know if it's the most expensive piece of equipment he'd have worked on - besides priceless data recovery.

author: Jwalling
author_rank: Unknown
timestamp: August 17, 2017, 09:55:55 pm
content: Quote from: tooki on August 17, 2017, 08:44:21 pmThis is a forum about repairing equipment.This particular thread is about documenting a repair on a piece of equipment, specifically an Agilent DSO8104A. Of particular interest to some (not you) may be the difficulty of replacing a chip entirely made out of ceramic with an unknown bonding agent that may or may not survive the process.With a little bit of luck, I'm hoping to see a Youtube video made of the repair process; this may interest some people (not you) as well.With a little more luck, I'm hoping for a successful repair.If you don't want to read this thread, then don't. I'm pretty sure no one is forcing you to read this (I'm not), but correct me if I'm wrong. Or not.

author: Cyberdragon
author_rank: Super Contributor
timestamp: August 19, 2017, 11:29:21 pm
content: Louis has his own forum, but I think it's a paid subscription. He probably stays over there rather than coming here and having "4chan" find him.EDIT: WAIT A MINUTE...is vze1lryy actually Rossman? If it is, I need to slap myself. (employees of his don't count, my point still stands)

author: Rasz
author_rank: Super Contributor
timestamp: August 20, 2017, 12:42:37 am
content: Quote from: tooki on August 17, 2017, 08:44:21 pmmarketing

author: retiredcaps
author_rank: Super Contributor
timestamp: August 20, 2017, 01:40:57 am
content: Quote from: Cyberdragon on August 19, 2017, 11:29:21 pmHe is.

author: Armadillo
author_rank: Super Contributor
timestamp: September 16, 2017, 12:55:46 am
content: What's Up with this work? Any updates?

author: bigeblis
author_rank: Contributor
timestamp: September 16, 2017, 07:02:03 am
content: Quote from: Jwalling on August 16, 2017, 03:59:31 pmSorry, English may not be very good.I've done this work. You need a far infrared auxiliary heating platform to heat the bottom of the PCB board. I'll heat it at 180 degrees, and then use the hot air gun over the top to heat it up to 260 degrees to remove the chip.Note: never hold the upper part of the film to move it, especially when the temperature is very high. Otherwise, the chip will be scrapped immediately. Only the bottom ceramic substrate can be clamped to move the chip.It is impossible to use only a hot air gun to disassemble the chip, and I have damaged the two chips.

author: Jwalling
author_rank: Unknown
timestamp: September 16, 2017, 09:36:01 am
content: Quote from: Armadillo on September 16, 2017, 12:55:46 amThe boards were received on 8/21/17.Last update on 8/30/17 is "It's still in progress. It's proving to be difficult. We will keep you posted once we have any news."So nothing yet...I'll probably shoot them an email this coming week.

author: KE5FX
author_rank: Super Contributor
timestamp: September 16, 2017, 06:03:18 pm
content: Quote from: Jwalling on September 16, 2017, 09:36:01 amWatching the TDS 694C repair, I was surprised that his idea of preheating was "stick the board in an oven for a while before putting it on the workbench." I wouldn't be surprised at all if he's discovering the limitations of that particular process.

author: Jwalling
author_rank: Unknown
timestamp: September 16, 2017, 06:08:22 pm
content: Quote from: KE5FX on September 16, 2017, 06:03:18 pmI'm hoping you're wrong!I let him know that one of the pre-amp hybrids on the donor board was known bad (put an X on it with a sharpie pen as well), and could be used to experiment with / get a heating profile.

author: Jwalling
author_rank: Unknown
timestamp: September 21, 2017, 05:11:11 pm
content: I just got an update.QuoteWell, that's a relief!So it looks like it's all done. Just have to pay and hopefully it'll be back next week for further testing/repair.Disappointed that there's no video.

author: Jwalling
author_rank: Unknown
timestamp: September 28, 2017, 05:18:32 pm
content: Update.Got the board back today. It now will complete a calibration (no more cannot detect cable so you can't proceed) But it fails CH1 trigger and vertical. Cannot get any kind of a decent trace on the screen...Further testing shows that there's a solder short on pin 20 to the large GND pad, see pictures.Checked it in four wire REL mode on my Keithley 2000, it's 60uOhms, so it's definitely between the pin 20 pad and the GND plane (no way can it be the chip or at the other end of the trace).The pad can be seen on the donor board.It looks like it's going to be heading back to NYCQuestion: Will performing the operation twice increase the likelihood of killing the chip? In other words are the heating effects cumulative?

author: PA0PBZ
author_rank: Super Contributor
timestamp: September 28, 2017, 06:02:49 pm
content: Looks like you also have some excess solder between 20 and 21? What about sucking the pin(s) clean with litz wire? With a bit of luck the short will be removed I'd guess.

author: TheSteve
author_rank: Unknown
timestamp: September 28, 2017, 06:04:34 pm
content: Preheat with a heat gun and use some really good solder wick possibly?

author: PA0PBZ
author_rank: Super Contributor
timestamp: September 28, 2017, 06:05:41 pm
content: Quote from: TheSteve on September 28, 2017, 06:04:34 pmSolder wick, that was the word I was looking forAlso I was thinking if you suck it clean and then still have the short put a piece of kapton tape in between and a wire from the pin to the track...

author: Jwalling
author_rank: Unknown
timestamp: September 28, 2017, 06:13:27 pm
content: Quote from: PA0PBZ on September 28, 2017, 06:02:49 pmI just measured pin 21 to GND and it's 1MOhm. Good spot though, I couldn't see it with my optical visors and never thought to look closer at the picture. A little flick with the end of an x-acto blade removed it. Not entirely sure it wasn't flux; there quite a bit of it remaining even after cleaning with some IPA.

author: wraper
author_rank: Unknown
timestamp: September 28, 2017, 06:14:56 pm
content: Quote from: TheSteve on September 28, 2017, 06:04:34 pmI'd say preheat the board if possible (borrow hot air from your wife), apply decent amount of tacky (gel) flux and solder the pad. Short will likely go away even without a solder wick.

author: PA0PBZ
author_rank: Super Contributor
timestamp: September 28, 2017, 06:16:01 pm
content: Quote from: Jwalling on September 28, 2017, 06:13:27 pmSo one non-existing problem solvedIf I compare the amount of solder with the IC above it he didn't really hold back...Pins 30 and 31 are also looking very suspicious on the picture.

author: Jwalling
author_rank: Unknown
timestamp: September 28, 2017, 06:17:59 pm
content: Quote from: TheSteve on September 28, 2017, 06:04:34 pmAnother good idea! I've got a nice tiny nozzle for my hot air station. Thanks Steve, I'll give that a try tomorrow.

author: vze1lryy
author_rank: Regular Contributor
timestamp: September 29, 2017, 04:55:03 am
content: Quote from: Rasz on August 20, 2017, 12:42:37 amWe 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.

author: Jwalling
author_rank: Unknown
timestamp: September 29, 2017, 03:22:34 pm
content: (Whining snipped)Quote from: vze1lryy on September 29, 2017, 04:55:03 amHi 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 tomorrowThanks.

author: Jwalling
author_rank: Unknown
timestamp: October 02, 2017, 10:14:52 am
content: 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.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.

author: TheSteve
author_rank: Unknown
timestamp: October 02, 2017, 04:12:02 pm
content: Ouch - I believe anytime you solder anything to a trace that is on ceramic you need to use silver solder.

author: wraper
author_rank: Unknown
timestamp: October 02, 2017, 04:35:43 pm
content: Quote from: TheSteve on October 02, 2017, 04:12:02 pmFYI 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.

author: PA0PBZ
author_rank: Super Contributor
timestamp: October 02, 2017, 07:26:13 pm
content: 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

author: Jwalling
author_rank: Unknown
timestamp: October 02, 2017, 07:30:23 pm
content: Quote from: PA0PBZ on October 02, 2017, 07:26:13 pmI 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!

author: Jwalling
author_rank: Unknown
timestamp: October 11, 2017, 05:07:57 pm
content: 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...

author: Jwalling
author_rank: Unknown
timestamp: October 11, 2017, 05:16:40 pm
content: 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.

author: Jwalling
author_rank: Unknown
timestamp: October 11, 2017, 05:21:36 pm
content: 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!

author: Samogon
author_rank: Frequent Contributor
timestamp: October 12, 2017, 12:01:10 am
content: I can try Amscope x40 with 5mp camera

author: Armadillo
author_rank: Super Contributor
timestamp: October 12, 2017, 01:43:36 am
content: 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.

author: AF6LJ
author_rank: Unknown
timestamp: October 12, 2017, 03:48:15 am
content: Good deal Jay, sounds like you are well on the way to having that scope back on the road.

author: Jwalling
author_rank: Unknown
timestamp: October 13, 2017, 02:45:04 pm
content: Quote from: Samogon on October 12, 2017, 12:01:10 amPM sent. Thanks.

author: Jwalling
author_rank: Unknown
timestamp: October 13, 2017, 02:50:17 pm
content: 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.

author: AF6LJ
author_rank: Unknown
timestamp: October 14, 2017, 02:20:41 am
content: Good deal.

author: Samogon
author_rank: Frequent Contributor
timestamp: October 21, 2017, 05:01:04 am
content: Jay, got your chip todayHere 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

author: AF6LJ
author_rank: Unknown
timestamp: October 21, 2017, 11:55:32 am
content: Nice shots, thanks for posting them.

author: charlyd
author_rank: Frequent Contributor
timestamp: February 14, 2021, 10:47:21 am
content: did it work after all?

author: Jwalling
author_rank: Unknown
timestamp: February 14, 2021, 11:27:20 am
content: https://www.eevblog.com/forum/repair/looking-for-someone-who-can-replaceswap-tek-tds694c-trigger-chips-for-$/