Author Topic: Looking for someone who can replace/swap Tek TDS694C trigger chips for $  (Read 10959 times)

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Offline Jwalling

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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/#msg791170

I 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.

Jay

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Offline Jwalling

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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.
Jay

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Offline kripton2035

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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/
 
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Offline Jwalling

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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/

Thanks! I'm in MA so he's about 140 miles or so from me. I'll fill out their request form in a moment.
Jay

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Offline Jwalling

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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.
Jay

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Offline nctnico

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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.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline Jwalling

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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.

A 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... :)
Jay

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Offline nctnico

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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.
A 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... :)
There 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.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline johnkeates

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This repair seems to be live streamed right now:
 

Offline nctnico

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OMG The way he swipes the pads with solder-wick is asking for trouble. It is very easy to ruin a PCB that way :palm: I 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 :palm:
« Last Edit: April 25, 2017, 10:59:08 pm by nctnico »
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline johnkeates

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OMG The way he swipes the pads with solder-wick is asking for trouble. It is very easy to ruin a PCB like that :palm:

I 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!
 

Offline rustybronco

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Nice watching Louis do his thing. He makes it look easy.
 

Offline TheSteve

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OMG The way he swipes the pads with solder-wick is asking for trouble. It is very easy to ruin a PCB that way :palm: I 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 :palm:

Clearly 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.
VE7FM
 

Offline vze1lryy

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OMG The way he swipes the pads with solder-wick is asking for trouble. It is very easy to ruin a PCB that way :palm: I 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 :palm:

I 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.

This board seems to have 1 lifted pad but that's the one with the burnt pin. So far so good!

It 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.
Louis Rossmann
Component level motherboard repair technician.
 
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Offline Armadillo

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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.
 

Offline Psi

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OMG The way he swipes the pads with solder-wick is asking for trouble. It is very easy to ruin a PCB that way :palm: I 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 :palm:

Pads 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.
« Last Edit: April 26, 2017, 10:04:16 am by Psi »
Greek letter 'Psi' (not Pounds per Square Inch)
 

Offline TiN

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Thumbs up for Louis for taking up the job :) Watched the thing  :popcorn:

He 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 :D.
YouTube | Metrology IRC Chat room | Live-cam | Share T&M documentation? Upload! No MB limit, firmwares, photos.
 

Offline NivagSwerdna

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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.  :-+
 

Offline nctnico

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OMG The way he swipes the pads with solder-wick is asking for trouble. It is very easy to ruin a PCB that way :palm: I 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 :palm:

Pads 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.
I 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.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline james_s

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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.
 

Offline Harb

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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.
 

Offline eKretz

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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.
 

Offline james_s

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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.
 

Offline nctnico

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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 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.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline eKretz

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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.
« Last Edit: April 29, 2017, 04:38:04 pm by eKretz »
 


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