Impossible to undo pcb screws, never had this one before
 

I suspect they deliberately used non-matching threads,ie cross-threaded,
despite disassembly ideograph of a screw on the pcb overlay and red
nail-varnish anti-shake lock.
Even 2 minutes of soldering iron tip on the head will not free the
locking .
And of course buried deep in the case surrounded by all sorts, that
block access, to grind flat blade slots in the screw heads or pairs of
flats for mole-grips etc.
Before grinding off the heads of these screws , any ideas to try.? Good
mechanical holding of this pcb is via a large bolt through the main
bridge
rect, that came away easily, then glue on the shanks of the original
screws would do for remounting. The retaining pillars for these pcb
screws are welded to the case bottom.
Before attacking wiht a grinder I'll try an impact driver, but that is
guaranteed to butcher the cross-head slot.
It might be easier to grind through the pillars as better access for
that angle, not decided yet. Then sleeve over the existing half pillar
for reassemble and glue to stop any rattling.

Impossible to undo pcb screws, never had this one before
 

Going by the slight hex shape under the case, these pillars must be Hank
Bush (TM) press fitted pillars , not welded.
Rather than silicon wafer colateral damage possibility from impact
driver shock, I'll try grinding into the base of one of those pillars,
to free the pillar with pcb screw. That keeps grinding dust out of the
elctronics. Then reassembly may be just countersunk head screw into the
pillar at the other end.

Impossible to undo pcb screws, never had this one before
 

That worked surprisingly well, just hoping the punch through shock of
each pillar moving impulsively did not do any electronic damage. Not
seen the pillars yet as will be marking the 30/40 or so headers and
crimps and photoing before disconnecting that rat's nest.
So method used. Clearly mark the hex shadow in the outer case paint.
Dremmel and .5mm grinding disc (no breakage) 3 cuts diametrically to the
corners of the hex, about 3 minutes per pillar . The centre will then
take a 3mm ball bearing. Then use a board over the amp and a clamp to
squash between board and ball. The ball punches through leaving a small
disk on the end of the pillar which hopefully will grind off easily when
I get the now loose pcb out of the case. The cuts reduce the metal and
allow seating of the ball.
Another impossible task in my portfolio, still learning about all this
stuff.

Impossible to undo pcb screws, never had this one before
 

Incompetent or deliberate filling the tapped pillars with proper
threadlock before screwing in , correct threads, then blinder blobs of
antishake lacquer on the heads. Needs more than 50W soldering iron, due
to heatsinking of the steel casing via the pillars.

Impossible to undo pcb screws, never had this one before
 

"N_Cook" wrote in message
...
I suspect they deliberately used non-matching threads,ie cross-threaded,
despite disassembly ideograph of a screw on the pcb overlay and red
nail-varnish anti-shake lock.
Even 2 minutes of soldering iron tip on the head will not free the locking
.
And of course buried deep in the case surrounded by all sorts, that block
access, to grind flat blade slots in the screw heads or pairs of flats for
mole-grips etc.

Might be worth reading the; "Best Philips screwdriver" thread.

Could be the crosspoint in the screw head is too shallow for the pointy end
of your screwdriver and the cross blades are only part engaging.

Screws can be tight, and a poor fit screwdriver will ruin the head.

Unless there's an overhead obstruction, you should be able to seat a drill
bit in the crosspoint recess and drill the head off. Removing the threaded
bit with only the thickness of the PCB to get hold of might be fun.

If you haven't chewed the heads up too much, drilling down with a pilot
drill smaller than the thread core diameter might allow you to turn it with
a regular Philips screwdriver. Or you could graze the pointy end of the
screwdriver a little with a grinder.

Impossible to undo pcb screws, never had this one before
 

In sci.electronics.repair, on Tue, 7 Feb 2017 21:12:57 -0000,
"Benderthe.evilrobot" wrote:


"N_Cook" wrote in message
...
I suspect they deliberately used non-matching threads,ie cross-threaded,
despite disassembly ideograph of a screw on the pcb overlay and red
nail-varnish anti-shake lock.
Even 2 minutes of soldering iron tip on the head will not free the locking
.
And of course buried deep in the case surrounded by all sorts, that block
access, to grind flat blade slots in the screw heads or pairs of flats for
mole-grips etc.

Might be worth reading the; "Best Philips screwdriver" thread.

Could be the crosspoint in the screw head is too shallow for the pointy end
of your screwdriver and the cross blades are only part engaging.

Screws can be tight, and a poor fit screwdriver will ruin the head.

Unless there's an overhead obstruction, you should be able to seat a drill
bit in the crosspoint recess and drill the head off. Removing the threaded
bit with only the thickness of the PCB to get hold of might be fun.

Use a reversible drill and left-handed drill bits. then theres a
pretty good chance you'll unscrew the screw before you get done
drilling. So you only have to replace the screw. Otherwise, you can
glue it back together later.

Also, there is another kind of screwhead/screwdriver in with crossed
slots, other than Philips. It's supposed to eliminate the need for
more than one size of such a screwdriver. I don't know any place these
scdrews are used by maybe you found one.

(Yes, I read the thread and know you finished this one but for next
time.)

If you haven't chewed the heads up too much, drilling down with a pilot
drill smaller than the thread core diameter might allow you to turn it with
a regular Philips screwdriver. Or you could graze the pointy end of the
screwdriver a little with a grinder.

Impossible to undo pcb screws, never had this one before
 

In sci.electronics.repair, on Tue, 7 Feb 2017 21:12:57 -0000,
"Benderthe.evilrobot" wrote:


"N_Cook" wrote in message
...
I suspect they deliberately used non-matching threads,ie cross-threaded,
despite disassembly ideograph of a screw on the pcb overlay and red
nail-varnish anti-shake lock.
Even 2 minutes of soldering iron tip on the head will not free the locking
.
And of course buried deep in the case surrounded by all sorts, that block
access, to grind flat blade slots in the screw heads or pairs of flats for
mole-grips etc.

Might be worth reading the; "Best Philips screwdriver" thread.

I can't find this. I looked back to before last June in SER, so where
can I find it?

Also the screw style I meant was Pozidrive. Could that have been the
difference?



Could be the crosspoint in the screw head is too shallow for the pointy end
of your screwdriver and the cross blades are only part engaging.

Screws can be tight, and a poor fit screwdriver will ruin the head.

Unless there's an overhead obstruction, you should be able to seat a drill
bit in the crosspoint recess and drill the head off. Removing the threaded
bit with only the thickness of the PCB to get hold of might be fun.

Use a reversible drill and left-handed drill bits. then theres a
pretty good chance you'll unscrew the screw before you get done
drilling. So you only have to replace the screw. Otherwise, you can
glue it back together later.

Also, there is another kind of screwhead/screwdriver in with crossed
slots, other than Philips. It's supposed to eliminate the need for
more than one size of such a screwdriver. I don't know any place these
scdrews are used by maybe you found one.

(Yes, I read the thread and know you finished this one but for next
time.)

If you haven't chewed the heads up too much, drilling down with a pilot
drill smaller than the thread core diameter might allow you to turn it with
a regular Philips screwdriver. Or you could graze the pointy end of the
screwdriver a little with a grinder.