Musical Fidelity P170 Blown Transistors

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AndrewT

R.I.P.
Joined 2004
Hi Rig,
is Pmik correct?
Are 2sj81/k226 the original fitment?

These are 2bolt Fpack packages.
The To247 Renases replacement are single bolt fixing and should be a straight swap. The Pin order is identical, but you'll need to move them sideways to align with one of the existing tapped fixing holes
2sj161/k1057 are the 140V equivalent.
2sj162/k1058 are the 160V equivalent, these are available from Rapid.
 
PMik

PMik

Member
Joined 2004
I would strongly advice you to change both pairs of MOSFET's to the 2SJ162/2SK1058 this to insure equal performance betwin the chanals ;)

An interesting detail regarding the 2SJ162/2SK1058 is the fact that the pair are equal to the 2SJ50/2SK135 pair
The 2SJ50/2SK135 where used in the MF B200, P140 and P150
Class AB standing current should be set for at least 100mA and imho for best sonic performance 200mA :)
 
R

rigel9999

Member
Joined 2007
neolio.eu
P170 MOSFETS purchased

Hi All,

I took delivery today of the replacement TO-247 FETS offered by http://www.profusionplc.com/subsites/exicon.htm

I'm somewhat confused as to which TO-207 replaces which of the original FETS

The replacements are marked;
ECX 10N20
EXC10P20

Can any of you please advise where each of these FETS sits on the board.
With the cover removed, I'm looking at the board on the rear of the case, there are four MOSFETS from left to right

1, 2, 3, 4

Which number corresponds to which of the above replacement FETS?

Finally, would you suggest I drill a nrw fixing hole to the rear of the case/cooling fins to attache the new single hole FETS or should I try to bend the pins on the new FETS and try to utilise one of the existing fixing holes?

Thank you all once again for your replies.

Christos
 
A

AndrewT

R.I.P.
Joined 2004
Hi,
if you use one of the existing holes, are the pins long enough to reach all three pads and go through the PCB for soldering?
The 2sj is the Pchannel part and matches the exc10p20
the 2sk is Nch = exc10n20

I suspect you have not downloaded the datasheets for either of these FETs. Go google them.
 
R

rigel9999

Member
Joined 2007
neolio.eu
Hi Andrew,
The pins are a little too wide for the existing board holes, I guess I shall need to drill them out a little.
I have lined up the replacement FETS and once they are sited over the pin holes on the board, the fixing hole is directly between the two original fixing holes.

O x O

O=original fixing hole
x=replacement fixing hole.

I guess with a little force, the FETS, after being soldered in place can be 'coaxed' into position to centre on one of the existing holes. Is this possible or will the pins snap?

I do not possess the ability to solder these in place as i can use only 1 hand and thus need to take my amp along to an electronics repairer.
I am making all these questions in the hope i shall have the answers if the repair guy encounters any problems.

Thanks again Andrew

Christos
 
A

AndrewT

R.I.P.
Joined 2004
rigel9999 said:
The pins are a little too wide for the existing board holes, I guess I shall need to drill them out a little.
I have lined up the replacement FETS and once they are sited over the pin holes on the board, the fixing hole is directly between the two original fixing holes.

O x O

O=original fixing hole
x=replacement fixing hole.

I guess with a little force, the FETS, after being soldered in place can be 'coaxed' into position to centre on one of the existing holes. Is this possible or will the pins snap?
Click to expand...
Do NOT ask anyone to bend the FET across to it's mounting hole after soldering.
Either
bend the legs individually until they line up with the pads and mounting hole before soldering.
or,
use very short jumper wires between the pads and the FET pins. The gate pin needs a resistor (gate stopper) to prevent oscillation in the FET and inductance of the connections. Use a resistor for the gate instead of a wire jumper and then short out the original gate stopper resistor. This method requires the pins to be cut fairly short, so the Technician needs to know what he is doing.
 
E

Evilbat

Member
Joined 2009
ianallenphotography.co.uk
PMik said:
The original Hitachi 2SJ81/2SK226 (2SJ82/2SK227) is no where to find and this has been a fact for more than a decade ..., solution use Hitachi 2SJ162/2SK1058 notice these FET's have different housing (TO-3P)
Click to expand...

Sorry to drag up an old thread with my first post, but my P170 has the Hitachi J162 and K1058's as installed from new. Obviously MF tweaked the design when they introduced the updated front panel design.
 
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