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

[R_J]

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

Thats good to know it works like this, this is just for testing and should not be left like this. So the problem is in that mute circuit, too bad you don't have the remote to toggle the mute line. I would check all of those digital transistors in that circuit, they can be hard to test but try and compare the readings between same numbered transistors. one might show a real difference.

[beetle1303]

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

I was overjoyed, and assembled everything back and enjoy the moment for a little longer.
I didn't mentioned it, but I did grounding at various points from pin30 CDC and output pin of Q507, Q508 and Q509. Only when output pin of Q509 is grounded then speakers sounded. So I think Q509 could be the culprit.
I ordered online a transistor meter, now waiting for delivery. I will do some testing with this new meter to see if I can pinpoint it. Will report back later.

[beetle1303]

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

You will have to watch out if the PRE_Mute is no longer in the circuit, it can get loud pop on the speakers and damage the speakers.

I was really excited to have sound!!

I didn't notice any popping sound when switching on/off the main power supply, nor turning from/to standby/on mode, neither when switching sources between radio and CD player. But I did noticed a low pop sound when turning the volume up and down!

Any idea when would this PRE-Mute line be turning on/off in a normal working system like this?

[budm]

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

You need the remote to see if you can turn Muting function on and off or not, may be it was stuck in the Mute mode when it was set by the remote Mute button. I do not see any info in the service manual for resetting the system to the default condition.

[beetle1303]

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

You need the remote to see if you can turn Muting function on and off or not, may be it was stuck in the Mute mode when it was set by the remote Mute button. I do not see any info in the service manual for resetting the system to the default condition.

I'm doubtful I can get a remote control locally...
Can you point out where is the remote control sensor input in the circuitry? Is it possible to force feed a voltage in to simulate an input from remote control?

[R_J]

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

Can you check the voltage on CN504 pin 3 (MUTE) this plug goes to the cd mechanism, maybe the fault is from there, Page 44 (pdf,47) has a LSMUTE line that should be 5 volts. There is a mute line from U501 pin77, that turns on Q522, that turns on Q521 that supplies ZD521. That MUTE line connects to R539 on page 41 (pdf,44)
So maybe that is where the problem is? Have you tried the CD? does it work?

[beetle1303]

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

CD (changer) works all along. Prior to grounding R570, radio and CD works in headphone mode, and after grounding, both radio and CD works with speakers volume.

Readings at CN504 pin3 (MUTE):
1) standby mode: 0v
2) power-on: 0v
3) switching/looping the audio sources:
Radio->CD->Tape->Aux
0v -> 5.14v -> 0v -> 0v
*noting that switching out of CD to Tape->Aux->Radio quickly the voltage remained at 4.95v, and dropped to 0v after 15-20s

I am not able to follow the rests of the circuitry to figure out what to measure and how to measure...

[R_J]

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

When you switch from Radio to CD, the mute line at CN504 changes from o to 5v. Check the voltage on Q507 base and switch from Radio to tape, Does the voltage change? Then check the voltage on Q508 base and switch from Radio to CD.
If the voltage on Q507 base changes, it should also change the state of Q508 and then Q509 which should change the Premute line.

[beetle1303]

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

Q507 Base voltage:
Standby mode: 1.2v
Power on: 1.1v

Radio: 1.1v
CD: 4.7v
Tape: 0.8v
Aux: 0.8v

Another word, switching in and out of CD, voltage changes. Switching in and out of the sources, no changes.

Q508 Base voltage:
Standby mode: 11.98v

Either at this point, or when I turn on the system while the red probe still on pin2- the fuse Blown!

Based on the attached diagram, base is pin2, correct? If not, could it caused the fuse to blow?

*I have 1 last fuse, so I should wait before continuing on Q508 and Q509.

[beetle1303]

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

I replaced the fuse, and decided to check on somewhere else to see if there is a +ve input to Q508. So I traced from U502 pin8 Mute to:
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)

Does it mean Q506 is problematic?

[R_J]

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

Q506 could be shorted, emitter to collector. With 0 volts on the base the trasistor should be open, and have no voltage on the collector.

I don't see how checking the voltage on Q508 base can blow the fuse

[beetle1303]

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

From what I googled: Q504,Q506 and Q506 are all PNP transistors, pin2(In) is base, pin1 (Grd) is emitter, pin3(Out) is collector.

At power-off, DMM set to 200KOhm, black lead on pin2(In), red lead on pin1 & pin3, the readings are:

Q504: 10.0 / 1(open?)
Q505: 154 / 45.4
Q506: 79.2 / 52.8

When I reversed the black and red leads (red on pin2)

Q504: 85.7 / 91.4
Q505: 1(open) / 1(open)
Q506: 22.1 / 70.2


Is there anything unusual about these readings?

[budm]

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

Are you checking those resistance with the AC cord removed from the outlet?

[beetle1303]

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

Yes, AC cord off the outlet, and power supply pack cable disconnected from the main board.

[beetle1303]

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

Also, some readings were instantly sat a stable reading, while others starting at lower number climbing slowly and stabilise at almost doubled the initial reading.

[R_J]

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

You will never find the problem doing this type of measurement. Any voltage left in the circuit from discharging caps, etc. will throw off the meters resistance readings.

[beetle1303]

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

Noted. Pardon my novice learning journey, every answered is a lesson learnt.

So these readings indicate if Q506 shorted or not? If not, how do I determine if Q506 is shorted Emitter to Collector?

[R_J]

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

I'm not sure what you are measuring here:

Q505: 1(open) / 1(open)

what does this mean????

1(open)? Are you saying it reads 1 Ω and YOU believe the reading is OPEN?

What is the reading on YOUR meter when set to ohms when the leads are not touching? This is OPEN
When the leads are shorted, What is the reading on the meter? this is a SHORT.
Don't use 200k range to check for shorts etc. in that range a wet noodle will check shorted.

Put your meter in diode test or the lowest range (200Ω), Check between emitter and collector of each transistor. If it is reading 1Ω, the transistor is shorted.

These are digital transistors (they have built in biasing resistors) so the will not check the same as normal transistors.
These have 10k resistors in the base so the will likely check open when testing.

[beetle1303]

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

My DMM - set to Resistance Mode, leads not touching shows 1, touching shows 0.

Reading on Q505: 1(open) / 1(open) means when the red lead is off, it shows 1, touching pin1 & 3 both remained 1 (nothing happened).

Set to 200Ω, it shows 1 and doesn't change.
Set to 2000Ω same thing.
Set to 20kΩ it jump up quickly then to 1
Set to 200kΩ then the numbers are readable.

Yes, my DMM is a diode/continuity mode. Leads not touching shows 1, leads touching shows 002 and beeps. In this mode, all readings taken are stationary at 1, one or tow readings will flash a number then stayed at 1.

So digital transistors like these should be removed from circuit in order to test correctly?

[R_J]

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

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.
The only real test you can do would be the resistance from emitter to collector and wheather it is a short or open. but you need to use the 200Ω range or use the diode test.
I had no idea the 1 you refered to was open circuit, what is the difference between 1 and 1? 1 being open and 1Ω being short?

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.