Looking for someone who can replace/swap Tek TDS694C trigger chips for $ - Page 1
Forum section: electronics / repair

author: Jwalling
author_rank: Unknown
timestamp: April 14, 2017, 06:06:41 pm
content: Does anyone in the USA have any experience swapping/replacing trigger chips in a TDS694C scope? Would need to be in the US.I've got one with an obviously bad chip (burnt pin) triggers properly on two channels, but doesn't on the other two.Passes SPC and full diagnostics; Amplitude is good to 3GHz as well.These scopes come with four chips, but will work fine with only two.See here for details:https://www.eevblog.com/forum/testgear/least-expensive-but-reliable-used-market-scope-with-at-least-1-ghz/msg791170/#msg791170I know that this is true, as I've worked on one myself for a customer that had only two chips, yet triggered fine on all four channels.The chip has a largish solder pad underneath the chip connected to GND on a 12 layer board, so proper equipment like a pre-heater is needed.Thanks.

author: Jwalling
author_rank: Unknown
timestamp: April 15, 2017, 10:08:04 am
content: More details of what's needed.1. I would like to have U1823 (the highlighted one with the blown out pin) removed and discarded.2. U1813 would be removed and put into U1823.3. U1833 would be removed and returned to me. Or perhaps whoever were to do the rework would want the chip and put it towards the total cost of the work. These chips when last available from Tektronix were $155 each.If anyone knows of any companies that do this type of one-off rework and/or what it would likely cost, that would be helpful as well.Thanks.

author: kripton2035
author_rank: Super Contributor
timestamp: April 15, 2017, 10:13:32 am
content: don't know if you're near New York but someone like louis rossmann can do this job. may be you can ask or visit him ?https://www.rossmanngroup.com/

author: Jwalling
author_rank: Unknown
timestamp: April 15, 2017, 10:37:23 am
content: Quote from: kripton2035 on April 15, 2017, 10:13:32 amThanks! I'm in MA so he's about 140 miles or so from me. I'll fill out their request form in a moment.

author: Jwalling
author_rank: Unknown
timestamp: April 15, 2017, 10:55:23 am
content: Just sent a request and pointed him toward this thread.Here's a picture of the entire ACQ board. It measures approx. 16" x 11"The area in question is highlighted in red.

author: nctnico
author_rank: Super Contributor
timestamp: April 15, 2017, 09:26:58 pm
content: If you have a hot plate and hot air this shouldn't be a hard job. The biggest problem would be shielding the FPC connector close to the chips. BTW I wouldn't mind getting my hands on a broken TDS694C myself but people are paying crazy money for them.

author: Jwalling
author_rank: Unknown
timestamp: April 16, 2017, 03:43:44 pm
content: Quote from: nctnico on April 15, 2017, 09:26:58 pmA hot plate like for cooking? Yikes! I don't think I would try that, there's a lot of SMD components on the other side of the PCB as well. You're braver than I am...

author: nctnico
author_rank: Super Contributor
timestamp: April 16, 2017, 04:00:39 pm
content: Quote from: Jwalling on April 16, 2017, 03:43:44 pmThere are hot plates for pre-heating or reflow soldering boards. What I (would) do in cases like a board with components at both sides or a board with through hole parts is put a piece of aluminium between the hotplate and the PCB at the location I want to heat. This keeps the rest of the board cool.

author: johnkeates
author_rank: Contributor
timestamp: April 25, 2017, 10:36:58 pm
content: This repair seems to be live streamed right now:

author: nctnico
author_rank: Super Contributor
timestamp: April 25, 2017, 10:53:30 pm
content: OMG The way he swipes the pads with solder-wick is asking for trouble. It is very easy to ruin a PCB that wayI usually try not to remove the old solder to reduce the risk of swiping the pads off with solder-wick. And then the way he puts the chip back again by heating the chip and not the board

author: johnkeates
author_rank: Contributor
timestamp: April 25, 2017, 10:57:24 pm
content: Quote from: nctnico on April 25, 2017, 10:53:30 pmI know right... but somehow he does the same on those multilayer laptop PCB's and that all works out fine. He probably isn't wiping/pushing/scraping as hard as you think he is.This board seems to have 1 lifted pad but that's the one with the burnt pin. So far so good!

author: rustybronco
author_rank: Contributor
timestamp: April 26, 2017, 03:28:03 am
content: Nice watching Louis do his thing. He makes it look easy.

author: TheSteve
author_rank: Unknown
timestamp: April 26, 2017, 03:46:10 am
content: Quote from: nctnico on April 25, 2017, 10:53:30 pmClearly he is used to working on high quality boards. I suspect he also has a pretty delicate touch with his level of experience. As a general rule of thumb never run wick across the pads though.Anyway, with a little experience and some decent tools swapping those chips is pretty easy stuff.I recall swapping BGA flash parts with a 1200 watt heatgun on 8 layer boards many years ago before I had any proper tools. I warped a few PCBs but never killed anything and the gear is still working today.

author: vze1lryy
author_rank: Regular Contributor
timestamp: April 26, 2017, 04:06:23 am
content: Quote from: nctnico on April 25, 2017, 10:53:30 pmI am not pressing down... but I am sure you can tell the force I am using from 8000 miles away... you do wick in the direction of the pad if you are using any actual level of force, which I am not. Use force to remove a screwhole from a groundplane, not here. Solder pads on iPhone boards pop off if you look at them the wrong way so "floating" rather than "pressing" is a must-have skill and feel if you are doing any of this.Quote from: johnkeates on April 25, 2017, 10:57:24 pmIt was lifted and off to the side, and is now straight and sitting safely where it belongs. I can get it burning, but it moving to the left post-burning was quite surprising to me.

author: Armadillo
author_rank: Super Contributor
timestamp: April 26, 2017, 07:20:35 am
content: Craftsman versus armatures really. No matter how the wipe and swipe, the pads and traces refuse to lift up. I think its also has something to do with the solder wick he used. Somehow I don't know whether its quality wick or not. For one, the solder wick is rather thick, second it didn't seems to soak up the solder quickly and filled the wick. The other observation is, he uses a lot I mean A LOT of quality solder flux that didn't appear to smoke. I don't think any of us use that many flux.And all the equipment he used are hidden at the angle. Wonder what hot air station he actually used at that time.

author: Psi
author_rank: Super Contributor
timestamp: April 26, 2017, 09:59:21 am
content: Quote from: nctnico on April 25, 2017, 10:53:30 pmPads coming off when you swipe with solder wick is ONLY a problem on- Really old PCBs.- Ultra cheap 1 layer rubbish from the cheapest dogyest china supplier.- Using an iron that is running WAY too hot for what you're soldering.The procedure is totally fine on modern PCBs when done with a light touch, especially in good equipment.And a light touch is all you need with good wick+flux.May i suggest that Louis has spent more time soldering than 99% of the people on here.He knows what works.

author: TiN
author_rank: Super Contributor
timestamp: April 26, 2017, 02:17:16 pm
content: Thumbs up for Louis for taking up the jobWatched the thingHe spend bit of extra time fiddling with the chips (those EQFPs easy to solder with getting tab done and then just wavesoldering pins row on each side, takes a minute to do, and maybe a minute extra to remove bridge on the corners). Surely recording and talking with chat people affects the flow, as off-camera he would do it in few minutes too.Now let's see if the scope works.

author: NivagSwerdna
author_rank: Super Contributor
timestamp: April 26, 2017, 02:36:05 pm
content: I find watching Louis work very therapeutic... in fact following his channel was a major influence in getting me playing with electronics again and SMD in particular.Good job.

author: nctnico
author_rank: Super Contributor
timestamp: April 26, 2017, 04:58:03 pm
content: Quote from: Psi on April 26, 2017, 09:59:21 amI do too. I have my fair share of (special) rework jobs under my belt including replacing surface mounted MOSFETs from multilayer boards without thermal reliefs. I know from experience that getting these too hot reduces the life significantly so heating the board instead of the device is essential for a succesful long term repair. In this case we are talking about chips which have run way too hot for years so they really need a lot of care and as less heat as possible to get as much life out of them as possible.

author: james_s
author_rank: Super Contributor
timestamp: April 26, 2017, 05:12:23 pm
content: I don't mind doing this sort of thing for myself and I'm usually successful but I'm very reluctant to do it for anyone else, unless there's a clear agreement that it's already broken and if I somehow manage to break it worse there will be no hard feelings. It's a delicate job and there is always some risk.

author: Harb
author_rank: Regular Contributor
timestamp: April 29, 2017, 02:53:00 pm
content: I have spent hours desoldering delicate doner boards trying to find the limits of solder pads and tracks.........I have used solder wick of all types and swiped them with varying pressures and never had an issue........unless the board has been previously heat affected.The most dangerous thing you can do to any board is use one of the spring loaded desoldering tools.....the shock of the mechanical action is a disaster for most boards if not done with care.......vacuum desoldering is the way to go there for sure.

author: eKretz
author_rank: Frequent Contributor
timestamp: April 29, 2017, 04:10:59 pm
content: I do a lot of repair and sometimes it is absolutely necessary to do a little swabbing with the solder wick to get a pad completely clean. I'm sure it depends on certain parameters, like maybe massive ground planes, etc.

author: james_s
author_rank: Super Contributor
timestamp: April 29, 2017, 04:16:42 pm
content: I haven't had any trouble with pads lifting so long as they're not overheated. Dipping solder wick in liquid flux greatly improves the performance.

author: nctnico
author_rank: Super Contributor
timestamp: April 29, 2017, 04:32:46 pm
content: Quote from: eKretz on April 29, 2017, 04:10:59 pmI try to avoid that; I prefer to reflow using existing tin. After all you can't really be sure how well the pads are attached to the board.

author: eKretz
author_rank: Frequent Contributor
timestamp: April 29, 2017, 04:35:56 pm
content: I definitely do also, but sometimes it just won't come off otherwise. I've tried all the tricks on the tough ones, including soaking the wick in multiple types of flux. I don't know if it's the solder alloy or what, but some can be a total pain and others will wick right off like they were waiting to jump ship. I absolutely do not use any down pressure, only just touch the pad and lightly move the wick to the side. Some still won't come up even after alloying with a ton of 60/40. Even with preheat. Admittedly I don't run into these every day, but they're out there.

author: Armadillo
author_rank: Super Contributor
timestamp: April 29, 2017, 07:31:11 pm
content: Will you consider his application of flux to be TOO excessive?

author: PA4TIM
author_rank: Super Contributor
timestamp: April 29, 2017, 07:34:01 pm
content: I use a gullwing tip to clean pads. If it needs to be cleaner than that and the risk is not high I use wick or a desolder gun. It is just a matter of experience and practice. (a steady hand and fine mechanics skills and good tools help a lot)And you must have confidence in your own skills.I also do pcb repairs, still rather simple cases to practice my skills. This is my most recent one:http://schneiderelectronicsrepair.nl/?p=481Not the most difficult one but for sure the most complex one. (pcb repair as in replacing pads, vias and (inner)traces ) I do not think there is a market for it but I really love doing it.

author: Dtec
author_rank: Contributor
timestamp: April 30, 2017, 01:52:58 am
content: Quote from: nctnico on April 25, 2017, 10:53:30 pmWell I have not seen him tear one off yetSent from my iPhone using Tapatalk

author: Dtec
author_rank: Contributor
timestamp: April 30, 2017, 01:54:35 am
content: Quote from: Armadillo on April 29, 2017, 07:31:11 pmIt works well for himSent from my iPhone using Tapatalk

author: ebclr
author_rank: Super Contributor
timestamp: April 30, 2017, 02:21:52 am
content: By the way, did the scope worked?

author: amb101
author_rank: Newbie
timestamp: April 30, 2017, 06:37:31 am
content: probably still in the mail. I'm sure we will hear when it all happens.....

author: Harb
author_rank: Regular Contributor
timestamp: April 30, 2017, 07:38:23 am
content: Quote from: Armadillo on April 29, 2017, 07:31:11 pmIts actually a good idea.......it helps avoid bridges and it tends to soak up the heat from surrounding components........it cheap enough and easy to clean, so why not pile it on.

author: SeanB
author_rank: Super Contributor
timestamp: April 30, 2017, 08:51:21 am
content: Too much flux will be if it is in a pile on the floor, after dripping off the bench.I have some small 10ml bottles with a dropper insert, that are perfect to dispense flux, and have a good number of them filled for use, just remove the lid, put on a drop where needed and put the bottle down. With the tiny dropper insert it is slow to evaporate the alcohol solvent in the bottle, but it goes fast on the board. When doing SMD work a drop before application of the iron to the component is fine, and same for every rework.

author: Jwalling
author_rank: Unknown
timestamp: April 30, 2017, 09:50:09 am
content: Quote from: ebclr on April 30, 2017, 02:21:52 amCurrently the board is in the mail. I'll be testing it this coming week.

author: Jwalling
author_rank: Unknown
timestamp: May 01, 2017, 06:16:16 pm
content: Quote from: Jwalling on April 30, 2017, 09:50:09 amJust arrived in the mail. I was going to wait till tomorrow to test it, but curiosity got the best of me in about 12.3 minutes.The results is a SUCCESS!! Louis, you are da' man!Nice work.Scope triggers great all the way up to 3GHz on all 4 channels!Thanks for all your help!Jay

author: rustybronco
author_rank: Contributor
timestamp: May 01, 2017, 07:50:31 pm
content: Glad to hear that!

author: nctnico
author_rank: Super Contributor
timestamp: May 01, 2017, 08:11:30 pm
content: For increased life do yourself a favour and put some extra heatsinks on the trigger chips.

author: Armadillo
author_rank: Super Contributor
timestamp: May 01, 2017, 08:33:35 pm
content: Any flux residue? LOL;Great job.

author: Jwalling
author_rank: Unknown
timestamp: May 01, 2017, 08:35:29 pm
content: Quote from: Armadillo on May 01, 2017, 08:33:35 pmActually, there is. I hope it's no-clean!

author: KE5FX
author_rank: Super Contributor
timestamp: May 01, 2017, 09:00:45 pm
content: Quote from: nctnico on May 01, 2017, 08:11:30 pmThey actually don't get that hot under normal conditions. If you pull the cover off the scope after it's reached operating temperature and take an IR snapshot before the board cools off, you will (or, rather,should) find that they're running under 50C-60C.The two great mysteries with these chips are why they fail in the first place, and why Tektronix seemingly included two extra ones on the board for no apparent reason.

author: Jwalling
author_rank: Unknown
timestamp: May 01, 2017, 09:25:16 pm
content: Quote from: KE5FX on May 01, 2017, 09:00:45 pmUsually catastrophically, IME. POOF!Quote from: KE5FX on May 01, 2017, 09:00:45 pmIndeed. And they're not just sitting there unconnected to anything either. They're connected to the GaAs MMIC switch chips and other circuitry as well. Weird... Would love to discuss this with the guy who designed the scope.Fun fact: The engineering code name for the TDS694C scope was "SCREAMER". I had one come through my hands a few years ago that had the word "SCREAMER" where the serial # should have been.PS: John, thanks for your assistance and encouragement off-line in all of this.Jay

author: james_s
author_rank: Super Contributor
timestamp: May 01, 2017, 10:53:57 pm
content: Perhaps there is some situation where all of the trigger chips are used, something that doesn't come into play in most normal use. Maybe it's only in certain models of the scopes that used that acquisition board? Maybe it was a feature they planned to use but never did? These are complex enough instruments that it's hard to say whether the performance is degraded in some way by a faulty IC even if it exhibits no apparent problems.

author: Jwalling
author_rank: Unknown
timestamp: August 16, 2017, 11:10:24 am
content: Quote from: Jwalling on May 01, 2017, 06:16:16 pmLooks like I have another job for Louis. This time it's an Agilent 1GHz DSO8104A with a blown pre-amp chip on CH1. The chip is all ceramic and has a large GND pad underneath the chip. I'll start another thread for this one in a bit.