[weblacky]

Hi All,
I’ve started the process of recapping my Tezro inventory.  I have two Tezros (one with confirmed power problems back in 2011) and I purchased a spare PSU for this purpose about 2 years ago.

I’ve successfully decapped the spare PSU, this process was actually much harder than at first glance would suggest.  Now I’ve only done an Indy PSU beforehand, and this layout hides the issues you’ll encounter due to changes in the PCB construction since that time.

I will post images of the disassembly soon to the image archive for others to see.

In order to get more room and measurements, I did desolder both daughter boards from both halves of the PSU.  However on the large board on the LV card did cost me two pads, I think these pads are stand-alone (as the bottom side has actual tracks to the them) so I think at this time I’m safe and they are stabilizing only.  But I’ll have to take measurements after reassembly to be sure.  It took 4 attempts to remove it.  That included add leaded soldering and 3-4 second soak times.  Still very hard, I don’t believe I’ll HAVE to remove it for a recapping normally, there are three caps of interest on that daughter board, only one of which is SMD electrolytic and I’m going to replace and I can get to the cap without removing the board.  I only did so for research purposes.

I can confirm just by my experience that there will never be a cap kit, because the chances of anyone without a desoldering gun with several tip types, a pin vice with 1mm drill bits, professional soldering iron, and stable 450F knife tip to cut through stabilizer, completing it successfully is near zero.  It took me over 3 hours (over several days) just to free all the caps due to 3 barriers, (give time I think I can get this down to under 2 hours):

1. Vias on this board are tiny, like 1mm, they are laid in very large (wide) tracks.  Clearing them is not possible with desolder wick, and if the component slips out of hole during heating, clearing a solder-filled hole is very hard.  I had to use BOTH soak time on the desoldering gun AND a 1mm drill bit with a pin vice to clear the remaining walls on some of the vias.

2. The power tracks are very wide and do a great job of heat transfer, you need to hold the desoldering gun on the component and wiggle, waiting for it to free up, then run the pump, while wiggling (as you’re supposed to do), and still several vias needed several reattempts as penetration didn’t take hold with the added reflow solder so easily.

3. One of the cap legs is just UNDER the structural component that holds a screw to one of the metal case sides, you must desolder the structural component, clear the via, then reinstall the structure.

4. There are several caps in between the DC output wires (forested), and they are glued together, trying to cut them apart or bring them out together without damaging the DC wiring is very difficult.  I still melted some wire coating by glancing touch…never got to the core (thank goodness).  This combined with some aggressive stabilizer gluing, means it’s a slow process where mistakes can damage stuff.




As it goes the PSU itself is accessible, but several components are hidden under large heatsink assemblies and while no Caps are, in the event of a failure, troubleshooting those areas is will hard (due to lack of access).  I’d again say the thing here would be to proactively replace caps and some of the resistors BEFORE critical failure.

From the Indy PSU research, If I see 1-2 Watt carbon resistors in the power path, I’ve decided to just replace them with higher wattage (same same) metal oxide resistors with flame retardant and temperature tolerance properties.  I’ve seen a few instances where these caps bake and change resistance after 20+ years.  Leaving one in a Tezro could mean a change in another 5-10 years after rebuilding.  We wouldn’t want that, so I’ll be experimenting with higher wattage, better heat tolerant resistors where I see them.

Right now I’ve just finished producing a cart on Digi Key with items, sadly I did run into two instances of prefect but out of stock scenarios and had to go with a backup Cap.  I’m not thrilled by this, but all inventories are low.  I checked those same caps elsewhere and they are also gone from other inventories as well (until like Dec this year).

I must go back over the list and revalidate my choices, then I’ll be buying enough cap for 5 power supplies worth of work.

I’m hopeful that a PSU rebuild solves my power issues on my first Tezro, I know I may need to replace a few board caps as well…that’s another project if this doesn’t fix it up. 

There are several on-board VRM circuits on the mainboard (not the daughter cards) that carry some Polymer caps, these are known to only have like a 15-year life span.  So, it’s possibly they are the cause of the VRM lower output issue, but since I’ve had additional issues (5V PCI AUX going low) as well…I blame the PSU first!

I’ve placed this thread here to keep it update in one place.  I’ll update more in a day or so after ordering and posting the pics I’ve taken of the process.

[robespierre]

When the thermal conductivity of the board is really high, as in your case, low-melting-point solder alloy can help a lot. (It goes under names like ChipQuik, SRA LowMelt, etc.) It mixes with the existing solder and allows it all to melt at a lower temperature, which means less heat conducted away through the board, which means less power required from the soldering iron.
I would also use a Metcal because it seems like power is a problem. A 60W Metcal (or other RF magnetic induction iron) is a lot more powerful than a 60W ceramic iron.

[weblacky]

I use T15 tips from hakko on an FX-951, the only ceramic tip technology is my hakko desoldering gun.  Technically these aren’t the new induction tips as I refuse to spend that kind of money without reason. I also get micro soldering features with this station so I don’t have to buy another station. 

These are the copper composite heater cores, fantastic - I never complained of heating with my iron, it’s great and also the same model all the YouTube stars use nowadays.  Zero reason to switch. I have resistive soldering stations for large heatsink as well.

I did this work almost solely with my hakko fr-301 gun, if you have reasonably priced, better gun, that uses improvements beyond ceramic, that’s advise I’ll take.  I will not trash my fantastic setup that’s taken me years to afford to switch my 10 or so tips to metcal.  And while if I went super-pro I’d stick with hakko as they beat out PACE and Metcal for supplies and tips I can readily get in the USA for fair pricing.

Also I use Kester leaded solder, like 63/37. That should be enough to mix, as mentioned.  I cannot afford to dump special low-melt in my projects. There is enough soldering on this board that I could run through like 1/4 of an small container of that stuff.   I only ever consider that on ICs I intend to reuse after removal.  

Otherwise heavily leaded solder should do find for the purpose of wetting exist joints.

[robespierre]

It sounded like you were having a lot of difficulty with the workpiece, so looking at tools and technique is logical. You can't learn soldering from "YouTube stars" (many like Ben Heckendorn and David Murray have no skill). Where there are videos of skilled soldering on YouTube, they are anonymous Shenzhen technicians or Eastern Bloc repairmen.

By the way, "heavily leaded solder" has a very high melting point. It was used as die-attach alloy (maybe still is for military components).

[weblacky]

Album of pics of Tezro PSU teardown is now up at: https://siliconimage.irixnet.org/index.p...o-PSU-Work

I wasn't complaining about my setup, I was giving advice that most people's setup will have this or WORSE results without Pro tools. I even used the short/large conic 1mm tip on my desoldering gun instead of my offset tip due to thermal mass requirements. Even so I've only seen a board like this one time (Cisco Switch Mainboard) where the vias are so small, that they JUST fit the cap legs, and are very hard to clear for both reasons of heatsink material and small diameter combined with depth (very thick PCB). This PSU cannot possibly have that many layers, yet it feels like it when I'm desoldering.

I wasn't implying I learned soldering from Youtube Stars, I simply mentioned it's a favorite station to a lot of known people. I learned soldering from the old NASA soldering instructional document as well as several certification videos I ran across for later IC package formats that are newer than the NASA document covers. So I take NASA as gospel for basic soldering.

Unleaded solder has a much higher melting point than leaded solder, not the other way around. Putting slightly MORE lead into the solder allows better flow and wetting, that's why I use a solder that has a lot of lead. I want results and longevity for my repairs, I'm saving something from a landfill, therefore I get us a slightly more toxic fix.

I do not run my desoldering gun on high (like 800F+). I only run it around 700F...closer to 650F. I'm ok with smoking time increasing over burning. I hate using high heat unless I have to as it increases the chance of lifting pads and scorching/mistakes. Since I use leaded solder is do not need to nuke everything, and less is more, I use slightly LESS solder (in accordance with NASA tutorials) then MORE. Most people use way too much.

I've just completed my third go through on the parts and have pressed buy on Digi Key. I should have the parts by later next week. Then the prep/cleaning/clearing will pay off in the reassembly. I'm crossing my fingers on this one. Thought I am curious about longevity after repair, 99% of them are from the same Nichicon family lines (as good as I could get) with like one rubycon...that was also a rubycon to begin with (same series). I assume Tezro PSU cannot be newer than like 2004? SO I'm wondering how far this will reset me to? I'm hoping beyond 15 years, at least, but I'm uncertain.

Also I'm trying to help the next technician in my rebuilds, I'm using less stabilizer and hopefully in a way that it's easy to gain access for separation when the next repair is needed. But I can tell that some of these designs require stabilizer for vibration/drop protection so you have to use some if you intend to ship them.

[weblacky]

I now have my parts order for five rebuilds worth of Tezro PSUs. I'm not done with my first rebuild (waiting for the free time), but after I rebuild my own, I should have two rebuild kits worth of parts for additional PSUs. I'll keep you all updated.

After my own, I should have parts for two more Tezro PSUs...should there be any takers. I'll update on the success of the first attempt soon.

[Irinikus]

I will be getting myself one of these before I start recapping my power supplies: (Or carrying out any smt repairs for that matter!)



@weblacky, thanks for showing the things that you do, as I'm sure the info will come in handy when I get around to servicing my machines!

[Shiunbird]

I will be getting myself one of these before I start recapping my power supplies

Wow this is beautiful - I appreciate proper tools.

[weblacky]

I will be getting myself one of these before I start recapping my power supplies: (Or carrying out any smt repairs for that matter!)



@weblacky, thanks for showing the things that you do, as I'm sure the info will come in handy when I get around to servicing my machines!

Make sure if you're attempting this to ensure you have these items:

1. A knife tip for your soldering iron, you'll need it set to 450F to melt (without burning) through the white silicone stabilizer (delicate process to NOT touch surrounding items).
2. An electric desoldering pump (gun)...Seriously, Tezro PSU vias are VERY small...you will never clear them with desoldering wick!
3. Even after desoldering correctly, about 4 of my vias still had partial blockage, needed a small 1mm drill bit and pin vice to ensure all vias cleared.

After that, you can improvise, but I do not see anyone completing the Tezro PSU without these above items. Also I add leaded solder (kester 63/37 leaded) to all joints and stay on the area about 3 seconds with my desoldering gun and wiggle to check that  the pin is free to move (fully liquified solder joint) before attempting a clear vias, heat transfer isn't nearly as easy as older boards.  I run my desoldering gun close to ~700F and my soldering iron at 650F.

I recommend you use both the default conic 1mm desoldering gun tip and purchase an extended tip (1mm & 1.5mm recommended) for very tight places!

Also a tip for the primary filter cap, melt through adhesive holding down cap on it's side first, then unsolder the small board from the larger one, then heat both legs of cap and use prying tool to remove cap while both legs molten, then clear large filter cap leg holes with desoldering wick (only time you can really do that outside of one other place).

I had to remove/solder screw holder (metal piece) on underside to access the cap legs in that area, be prepared for that too.  Otherwise, it's like it seems.

[weblacky]

OK, I had time today to try to put all the parts back in. My part notation had some issues and I had trouble with my parts and as it seems I may have duplicated parts or confused very closely rated parts when ordering (ordered too much in some cases). I've soldered every cap in, but I've left the daughter board on the LV PCB off and I will be going back over my spreadsheet (discovery) and cross-checking every cap I installed with that sheet to ensure I rectified my labelling screw-up. I guess that's what happens when you order parts after midnight :-)

So that will slow me down a little. I will say that I was grateful to have fully cleared vias...but soldering vias into large ground planes was still problematic (while trying NOT to overheat a leg/component in that via). This only occured about maybe 4-5 times. But it's a kind of issue. A part of me wonders if for quality and speed, it be better to use a hot air wand to preheat the grounding plane a little, it would definitely slow me down (as you cannot do them all at once without a jig of some kind to hold the parts).

Anyway, it wasn't the biggest deal. I'm kind of afraid to start the PSU given the changes and first-time experience on this model (that it won't run...you don't want your first repair experience with a new piece of equipment to go wrong...it's demoralizing). So cross-checking will buy me time.

I will say that given the need to remove the two daughterboards and the thick ground planes, I don't know (even with practice) how fast one can really do this board. The Indy's by comparison go very fast (from a soldering perspective). Also I replaced ALL electrolytics on this PSU (even on the daughterboards).

I'll update as I get closer and all that! I really need my Tezros to work anyway...so I'm motivated, just given the difficulty, it's kind of a labor of love...I doubt in terms of a service people really want to pay what it takes for time on these. Right now I doubt I can do one in under 3 hours.

More to come....