[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.