Nakamichi Soundspace 5 - headphone works normal, both speakers volume very low at max

[beetle1303]

Re: Nakamichi Soundspace 5 - headphone works normal, both speakers volume very low at

My DMM will show minimal of 3-digit number like 11111, 111, 011, 001, etc. So 1Ω will be 001 and open will be 1.

OK. Voltage check means power-on and take readings would be like what I reported in post #30?
Q504: pin1 0v, pin2 0v pin3 0v
Q505: pin1 11.9v, pin2 0v, pin3 0v
Q506: pin1 11.9v, pin2 0v, pin3 11.9v (switching from radio to CD to tape same readings)

These readings were taken with black lead on chassis ground, and re lead on each of the 3 pins.

Can I test if Q506 is shorted Emitter to Collector by putting red lead on Emitter and black lead on Collector? Or how should I take the reading?

[beetle1303]

Re: Nakamichi Soundspace 5 - headphone works normal, both speakers volume very low at

For my education and future references, could you help by labeling the Base, Emitter, and Collector in those transistors in the diagram attached?
Thank you, appreciate very much all the lessons thought.

[R_J]

Re: Nakamichi Soundspace 5 - headphone works normal, both speakers volume very low at

just Google transistor pinout

It IS rocket science. If the emitter arrow points away from the base it is NPN if the arrow points toward the base it is PNP

[beetle1303]

Re: Nakamichi Soundspace 5 - headphone works normal, both speakers volume very low at

I can see quite clearly from physical drawing of the transistor and which pin is waht, but from the schematic I sometimes get confused between NPN and PNP where the label for pin1 and pin3 are reversed, or sometimes labelled as Grd, In, and Out..

Anyway, take a bit of time to sink in. Thank you.

Kindly advice again how do I test if Q506 Emitter to Collect is shorted?

[beetle1303]

Re: Nakamichi Soundspace 5 - headphone works normal, both speakers volume very low at

I bought a new DMM that can measure diode and capacitor.
Here is the new set of readings in diode mode:

RED lead on pin2:
pin1 pin3
Q504: 2.36v 2.69v
Q505: OL OL
Q506: 1.89v 2.25v

BLACK lead on pin2:
pin1 pin3
Q504: 1.51v OL
Q505: OL 2.65v
Q506: OL OL

RED lead on pin2 / BLACK lead on pin3:
Q504: OL
Q505: 2.23v
Q506: 2.51v

BLACK lead on pin2 / RED lead on pin3:
Q504: 2.33v
Q505: OL
Q506: 2.69v

Again, I have idea what these readings mean, hopeful is of some use to spot the problem.

[R_J]

Re: Nakamichi Soundspace 5 - headphone works normal, both speakers volume very low at

I tried to explain this, before maybe google translate is having a prolem?

These digital transistors can not be checked in or out of circuit because they have a built in resistor in the base circuit. When you check a normal transistor, you use diode test because it applies more voltage across the junction so you can measure the voltage across the junction. in most cases .6xx volts. (similar to measuring a diode)
But because of the 10k resistor in the base you can't measure the forward voltage drop of the junction. the transistor will check like it is open.

Transistor pins are labeled E, B, C, NOT 1,2,3 !

[R_J]

Re: Nakamichi Soundspace 5 - headphone works normal, both speakers volume very low at

The only transistor in that circuit you will be able to check using diode test is Q507. With the meter knob in Ω, You may need to push the SEL button to get it to diode mode. If it is in auto it might think its check a capacitor.

[beetle1303]

Re: Nakamichi Soundspace 5 - headphone works normal, both speakers volume very low at

This is why voltage checks work better. Take Q504 for example. this is a digital switch. the base controls weather the switch is on or off
with 0 volts on the base, the switch is OPEN
with about 2~5 volts on the base the switch is CLOSED

When the there is 2~5 volts on the base and the switch is closed, the collector is shorted/connected to the emitter and in this case ground.

My apology for not reading your input in it's entirety. I was eager to find out more after reading this statement, and bought a new DMM to try...

I am planning of doing 2 things now:
1) Find a remote control to check if it would have any effect.
2) Get a trashed circuit board with the same SMD transistors to practice de-soldering and soldering back. If I can get this task done correctly, I would attempt to replace Q506, Q508 and Q509.

Do you think this is a logical next steps? If not, what would you recommend ?

[beetle1303]

Re: Nakamichi Soundspace 5 - headphone works normal, both speakers volume very low at

While scouting around for a remote control, a highly unexpected but most pleasantly surprise encounter: someone donated a complete SS5 with both remote controls absolutely free of charge! Other than radio tuner doesn't work, every else works perfectly!

Here is the most anticipated test - whether remote control would un-mute the muted speakers: unfortunately, NO...

So I swapped out the donor tuner with mine, and now I have a complete and fully working Soundspace 5 !!!

I decided not to pursue replacing those transistors as I really don't have the skills to do it right.

Thank you R_J and others who helped and guided me the entire journey.

However, I do want to see if the tuner module can be salvaged. When powered up in radio mode, the tuner simply producing constant hissing noises scanning across all frequencies. I removed the tuner module and visually see a patch of black soot on the metal cover. Removing the cover, there is a slight deposit of black soot on top of the big cylindrical component. I checked the service manual but can't find any schematic on this TU101 module.

Any idea if this is tuner module is salvageable ?

[R_J]

Re: Nakamichi Soundspace 5 - headphone works normal, both speakers volume very low at

I doubt you will find a schematic for the tuner pack, You can get the ic pdf's and you will see what there functions are, It is not likely it will be easily repairable. If that "soot" was due to an electrical arc on the module it's hard to say what it damaged, but without a scope I don't see how you would check the circuit.

[beetle1303]

Re: Nakamichi Soundspace 5 - headphone works normal, both speakers volume very low at

OK, then I believe this will mark the end of learning journey for this system.

Once again, thank you very much @R_J (the all the rests) for all the guidance and knowledge sharing. It's been educational, and I will definite return with other learning project.

Cheers everyone.