old Sessionette 75 Mk 2 - no output

[Bushbaby]

Ok, I have removed these and retested.
I haven't a clue to interpret these values against the data sheets? Do the data sheet cover them when powered up to read the values? 
One thing that seems apparent from my limited knowledge is the black 2SK226 does appear to be missing the diode between the source and drain connection or am I incorrect? Does this suggest that this one is actually faulty??

Could these be upgraded to the current equivalents (if they exist?). Otherwise, this will definitely have to go to Award- Session for repair / upgrade.

Best Regards

Rob


       

[Murphyv310]

Well is should have the diode and either it's faulty or the tester isn't for some reason not picking it up. It should be measurable on a standard diode test but make sure the gate is discharged.

[Bushbaby]

I have got this correct I hope, I initially placed a lead between pins 1 & 3 of the N-Channel Mosfet 2SK266 and used my other multi-test unit to see what the values would be (see attached). Again, no diode shown - does this indicate that this mosfet is kaput??

Best Regards

Rob


       

[Murphyv310]

Hi.
Best way is to short all three legs together with a suitable crock clip or whatever you have. Ideally you need it on an antistatic mat with you at the same potential, remove the short then measure between source and drain with a dmm on diode test then reverse the connections and do the same, report what you find.
Now to the very same with the other MOSFET and see if there is any difference noting what way round the dmm leads are connected

[Bushbaby]

I hope that I've recorded this correctly, the readings are as follow (pin 2 source, pin 3 drain) using UNIT-T UT61-E DMM set on diode test
2SK226 (Black) N - Channel MOSFET.
- source to drain = 0.1358 V
- drain to source = 0.0L V
2SJ82 (Green) P - Channel MOSFET
- source to drain = 0.0L V
- darin to source = 0.2858 V

I hope this helpful?
Best Regards
Rob

[Murphyv310]

The opposite readings between n and p channels is correct. The 0.1358v though seems low which might effect the transistor tester results. I'd replace it although my advice still sticks to send it on a wee journey.

[Murphyv310]

Incidentally the originals are available in the UK, for around £60 + the chancellors commission.
Beware Chinese cheapo's.

[Bushbaby]

There is virtually no chance of obtaining replacements for either of these obsolete MOSFETS. I cannot even find equivalents or upgrades to replace them either. It does appear that this will have to go Award- Session after all. They do offer a replacement board for £59.99 but as I indicated earlier, if there is an issue with preamp too it could affect the power amp so its not worth just buying the power amp module. I will discuss with my friend what he wants to do with it - its a shame really at the end of the day.

Best Regards

Rob

[Bushbaby]

Just a thought (maybe no chance) could I replace this with a possible modern MOSFET? Obviously it would have to be of a very similar specification.

Best regards

Rob

[Murphyv310]

Personally I feel I've gone far enough with advice here on the thread and one to one.
Im sorry but I'm not contributing any further.