CA-1010 -30Vdc output phono stage

mbz

Addicted Member
Intermittent problem where approx -30Vdc output from right channel phono stage
(between FR104, FR106).

Power rails ok +/-31Vdc. TR110, 12, 14, 16, 18 replaced. D102 (VD1212) replaced.

Recaped, solder joints/bridges/shorts checked ok.

Approx -30Vdc on FR102 (either side), FR102 replaced with metal film
TR112 Vb-e approx 0.2Vdc
TR114 Vb-e approx 0.0XVdc
TR116 pulled, still high dc present.

TR106,8 Vb-e's look ok 0.6-0.7V, b&e voltages in line with other channel

TR104b approx 12Vdc
IC104 pin 6 approx 14.6Vdc

Plan is to replace IC104(2SK100) with other channel

Has anyone come across this problem before, ie, high dc on phono stage?
Also, 2SK100 is no longer available, having problems finding the datasheet (yamaha internal).
I would expect that these are two closely matched FETs. Any significant drawback with
replacing the IC with individual FET's? Recommendations? Donor amps are rather expensive in AU.
 
Problem confirmed, switched IC103 and 104, abnormal voltage moved to left channel.

AK search did not reveal much. Talk of someone having the datasheet, appreciate a
copy or parameter details. DIYAUDIO post suggests 2SK389 or 2SK170 (both obsolete)
as possible replacements, maybe work off those datasheets???
 
If you have a Peak DCA you can check each FET.
Sounds like time to buy some more test equipment.

This fault was particulaly annoying, amp would power up ok, phono stage fine for anywhere 1sec-10minutes then fallover
and then recover or even stay faulty. Intermittent/inconsistent=annoying.
 
Sounds like time to buy some more test equipment.

This fault was particulaly annoying, amp would power up ok, phono stage fine for anywhere 1sec-10minutes then fallover
and then recover or even stay faulty. Intermittent/inconsistent=annoying.
Pretty much slamming the rail to output.
 
you said it is 2SK100
Which one ?
2SK100 (IE100600)
2SK100A (IE100900)
2SK100C (IE101130)
2SK100D (IE101140)

?
 
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First up, thanks for all the input, greatly appreciated.

I do have an A-1 that I had planned to refurb (one day). I'm tempted to lift the 2SK100 from that and investigate a discrete solution for the A-1.
My main motive for participating in AK is to learn, maybe time to learn about FETs....

Can confirm that it's the 2SK100 (IE100600). So a datasheet or parts recommendations (SMD ok) would be appreciated.
 
DIYAUDIO post suggests 2SK389 or 2SK170 (both obsolete) as possible replacements, maybe work off those datasheets???

If the 2SK389 will work for you, I can pull one from a parts amp of mine and throw in an envelope.

Let me know.
 
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Thanks for the effort guys. Really chasing the FET's characteristics IDSS etc... I have not "studied" FETs but they appear to be just a choke device, ie,
voltage at gate restricts flow between S&D. That said makes me wonder what impact if any they have on sound quality, by that I mean the IC package\versus discrete items. OK the IC will be closely matched pair but discrete FETs should(?) work. Like I say, time to learn about FETs...
 
Oldsansui441, thanks for the offer on the 2SK163, need to do some homework first. Like I say, I'm treating this as a learning exercise.

Clinic-audio, brilliant, thank you.
 
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