Are any of these transistors have to be replaced? ( HK CD401 )

[xchg.ca]

Hi guys, this is a list of transistor I have in HK CD-401 deck

It suffers from low record/playback level
I have found and replaced leaked caps ( 10mFx16V and 1mFx50V )
I also found that 2x2SC2878(B) in rec-mute circuit were partially opened all the time regardless of button ( at the moment they just removed )

Here is the list of all transistors of the deck. I did search and cross reference with a list posted in forums. Seems like there are no know bad ones on my list! But may be I've missed some?

HK CD 401 list of transistors

Main Board
2SB855(C)
2SC2603(F) X3
2SA1115(F)
2SC1419(C)
2SD2236(Y)
2SA1115(F) OR 2SA1115(E) X10
2SC2603(F) OR 2SC2603(E) X35
2SC2320L(F) X4
2SD667(C)
2SA999L(F)
2SK163(M)
2SB647(C)
2SC2878(B) X2

LINE AMP, MIC BOARD
2SC2320L(F) X2
2SA999L(F) X2
FET - 2SK170(GR) X2
FET - 2SJ74(GR) X2
2SA984(F) X2
2SC2274(F) X2
2SC2603(F) OR 2SC2603(E) X2
2SC2603(F)
2SC2320(D) OR 2SC2320(E) X2
2SC2878(B) X2

Logic Control board
2SC2236(Y) X3
2SA1115(E) OR 2SA1115(F) X5
2SC2603(E) OR 2SC2603(F) X7

HX PRO BOARD
2SD667(C) X2

PB EQUALIZER
2SA1190(E) OR 2SA1190(D) X2
2SC2855(E) OR 2SC2855(D) X2
2SC2320L(F) X2
2SA999(F) X2
2SC2603(F) OR 2SC2603(E) X2

ELECTRONIC COUNTER BOARD
2SC2603(F) OR 2SC2603(E)

TORQUE CONTROL BOARD
2SC2320(F) OR 2SC2320(E)

 

[elnaldo]

There is a thread here at AK, about the "top ten noisy transistors" , which has more than 10 transistors known to fail after so many years.

If you find in that list some of the parts present in your unit, you could replace them as a preventive maintenance.

If, not, let them be, just find the problem and fix it. You can introduce literally hundreds of new problems, very hard to trace, if you start to replace all those transistors without a reason.

 

[HPMguy]

Replacing all the electrolytic capacitors is likely to do much more for you than replacing all the transistors, especially since some may be difficult to find replacements for.

If you had some leaked low value capacitors, I'm betting every single similar capacitor is bad. I don't have a schematic, but very likely you have capacitor coupled signals, and if those capacitors are bad, you will have low output and low recording levels if it works at all.

Do the re-cap and check the power supply, fix anything there, and then see how it works. Likely all the transistors are good unless something shorted from the leaked caps.

 

[petehall347]

first thing is try a pre recorded tape that is known to have good levels . if playback still low look for something in common with rec playback . if both channels first suspect power supply issues .
another thing is record on it and playback on another machine if possible . .

 

[xchg.ca]

Thank you guys for suggestions.
I did replaced all questionable caps! Also found someones mishap with some previous repair. They mixed up one channel coupling cap 10mFx16V with 1mFx50V... not that big of a deal, but still that was wrong.

I did not plan to replace transistors w/o reason, that is why I'm asking community to see if there any know bad ones in my list
I did check prior to posting with another thread here listing about 15 transistors. None of them were found in my list. But may be that list is incomplete?

 

[roger2]

...

I did check prior to posting with another thread here listing about 15 transistors. None of them were found in my list. But may be that list is incomplete?

IMHO that list is more than complete. To put it another way, I have amplifiers with several of the transistors in the list, and none of those transistors have caused any issues. I don't doubt the reports of failures that landed some of those transistors on "the list". The list is an asset to AK'ers and kudos to dlucy for creating it. But it is too easy to over estimate the true scope of the issue with the way the list has been compiled. If 5 people report transistor 2sa9999 "going noisy" it might make the list....but what about the other 10,000 2sa9999 transistors out there quietly doing their job and still working fine? Perceptions can get skewed very easily.

On the other hand, the impulse to knee-jerk-react out of fear and replace everything in sight is a problem, and much more likely to create issues than leaving things alone. Recapping electrolytics is generally a good thing (although some make a case against it), but we now have examples of guys replacing every cap including film and ceramic caps, every carbon film resistor, and every transistor. I have seen some threads where a BOM is created and ordered before a "new" amp/receiver is even delivered. It is crazy. It is the opposite of wisdom....and wisdom is what you have received in previous posts in this thread. Focus on specific problems, replace electrolytics (or tanalums if it has any). Be happy and move on to the next project...


Welcome to AK

 

[elvi]

Remember.

Semiconductor technology and quality evolved from the 1970s . My CD player might not have any suspect parts