Roksan Kandy LIII amp , 2 years old
N_Cook
http://community.whathifi.com/forums/t/313192.aspx
and would rather I looked at it rather than the maker
Easy to blame PbF as printed all over as such.
Problem is different to that above thread. For ages now the R ch has failed
occassionally at switch on. Switch off and most of the time it comes up.
Very rarely that ch dies in use, Then last week both ch failed at sw on , so
he decided something needed doing
Anyone know how to find mechanical data on 16 amp output relays
Make Finder 40.615 , clear cased so can see the contact gaps
About .75mm for the R one and .5mm or so for the L. Thinking fine contact
contamination and not enough mechanical punch-through.
Both relays in series from one supply and TA3717 ptotector IC
Or any other ideas other than checking phones socket, if wired in to affect
output somehow, PbF solder looks fine. Wanging with engraver and nylon bolt
has only highlighted a microphonic capacitor.
Looks like another amp where I'll make an LED mod that the owner can view
through the phones socket. Bring out pcb mounted, relays-on LED ,and add a
different colour one for the main rails supplies on, both viewable through
the phones socket transparent plastic panel at its rear
N_Cook
N_Cook
Phones uses switched ground contact for cutting speaker output , via relays,
so not a
suspect now. Can see why there are "pot" problems with these amps but not
this one - YET. The PbF soldering on this board looks terrible compared to
main board , no chance of the "green ring" of concave sided volcano mirror
PbF finish here under a 30x . Matt grey crystalline and cracking solder so
the "ring crack" of PbF likely in a few years with normal localised user
induced vibration from using phones or turning the vol knob.
A technical issue - if anyone is up on the matter as twice in one month ,
different makers. I've found PbF solder being used on boards apparently made
from substrate not specified for PbF , or rather the extra temperatures/heat
reached in the soldering process.
From the UL.com E number and type number these amp boards are tin-tinned for
PbF use but the board material is rated 260 deg C/ 8second dwell (270 /10
for PbF , 260/10 for SnPb and 288/8 for polyimide high temp material ) so
lower spec than the already lower spec (8 second dwell time) of traditional
solder formulation boards.
N_Cook
+/-15V rails but one pole contacts welded closed. Supply side cap 220uF/
25V and switched line has 68uF/35V which is blown on the permanent welded
set of contacts, other rail ok so far. There is 000 ohm resistor down stream
of each contact , any suggestions of ohmage to try replacing it with now
the relay is out for replacement? contacts are 1 amp DC rated and is
probably just supplying 4 dual opamps and no transistors or anything else
active in the phono preamp and tape-in and tape out section. Presumably in
the range 2R to 15R in each rail to limit switch on current. Presumably all
those , user unused , opamps were permanently "powered" unipolar, never
checked phono inputs on initial testing