Thanks! This one is typical for a previous attempt to repair using TH components, with a few lifted pads. But yes, once you fix the traces and replace failed or damaged passives it just works. It's usually far less involved if no repairs were attempted.
C12 and C14 should be bi-polar capacitors, but i don't see anyone using them. If you look on the board C12 and C14 have no + sign either. So they should be BP type capacitors. Does it matter ?
Non-polar caps use the same package as regular, so look the same except they don't have polarity marking on top. And yes, originally they're non-polar types, as they see AC sine wave across them. I usually leave them alone if they are factory as I've never seen them fail. I read a research paper a while ago that describes what happens to the capacitor when AC voltage is applied, but can't locate it now. The gist is that significant reverse voltage applied over time dissolves the oxide layer that serves as the dielectric, causing the capacitor to eventually develop high leakage which may lead to thermal damage in many applications. The higher the voltage relative to rating, the quicker the process is. However, if the capacitor is not damaged, applying correct polarity restores the oxide layer, so applying AC voltage at amplitude that's a small fraction of the capacitor rating does not immediately destroy the capacitor, as the correct polarity pulse restores almost all of the damage caused by the reverse polarity pulse. It's unclear how to derate the expected life in this scenario, so it's hard to estimate how long a polarized cap will last in this circuit. Here it only typically gets a couple volts in reverse, so if the cap is rated at 25 volts it could last a long time.
I used this www.stewmac.com/electronics/shielding/conductive-copper-tape/, you can find more on Amazon or Mouser, search for "copper tape" or "copper foil". I scrape off the adhesive on the back and clean up with IPA. I'm yet to find a suitable glue - nothing I've tried so far (epoxies, CA, cements) bonded to copper strong enough to withstand heat and mechanical stresses. I created a custom copy of the capstan PCB and waiting for the order to arrive. I think going forward I'll use the same process as my Dolby daughtercard rebuild instead of patching up the pads. Transferring all components over to a new board could be quicker than fixing up all the damaged pads.
@@bonno666 here are gerbers for JLCPCB github.com/quietcat/tascam238s/tree/main/capstan-pcb/238-capstan/gerbers There is a Kicad project too in the parent folder. Or if you like I can send you one from my order
