Nikko Beta 40 relay not click. Need help.

[ReisDaddy]

I bought Nikko Beta 40 pre amp and the seller said it is working. But its not, but i dont want send it back since its hard to find.
I think the relay is not clicking.

Trying to isolate, is this what i do is correct?
I pull the bridge rectifier D801 and D802 except to the relay which is D803.
I did check all transistor and caps and resistor, so far its looks good reading.

What i already replaced:
C901 new 100uF, old was reading 80uF
C826 new 33uF , old was reading 48uF
Q901 Transistor 2SC1845 to FairChild C1845.

But im still confused, the relay still not clicking.
This is protection relay, am i right?
I did pull the relay to check it doesnt has clicking sound? Looks like big IC. Supply it with 12v to the coil symbol and using DMM with beep mode it is working.



When power on, the relay coil both pin is 15.9v. After delay around 5 seconds, they both drop to 12.2v
Is it normal?

And in transistor Q901 SC1845 pins:

PIN	Power ON	Delay 5 secs
RELAY RY901
COIL 1	15.9v	12.3v
COIL 2	15.9v	12.2v
Q901 SC1845
E	0.0v	0.0v
C	15.9v	8.3v
B	-1v	0.66v

Here is the schematic.




Please help, 4 days cannot find the problem. I will post any information needed.
Thank you so much.

UPDATE 2024.08.05
As i promised to give information after full recap and cleaning back of the pcb, hope will help future owner with same problem.
My solution was replace:

Parts	Service Manual	Physical	Replace
D804	1S2076A	1S2076A	Fairchild 1N4148
D902	1S2076A	1S2076A	Fairchild 1N4148
Q901	2SC1845	2SC1845	Fairchild C1845

Here is the final DMM reading:
Please note:
RED is previous reading
BLUE is the final working condition
Muting relay clicks around 8 secs.
Q901 Collector reading is decreasing When powered 14.4v, after 8 secs around 6.1v then until 0.95v





Thank you for AK members for helping me.

 

[p4spooky]

1. Check the relay off circuit - with a 12VDC power supply
2. Check R903 - does is measure 220R?
3. Check D901/ZD901 and R902 just to be safe

I think 8.3V on the collector of Q901 is too high (had it as "low" before the edit)

 

[ReisDaddy]

1. Check the relay off circuit - with a 12VDC power supply

Sorry, but i already sai: I did pull the relay to check it doesnt has clicking sound?
Supply it with 12v to the coil symbol and using DMM with beep mode it is working.

2. Check R903 - does is measure 220R?

Checked 220 ohm

3. Check D901/ZD901 and R902 just to be safe

R902 checked 150K ohm
Also checked D901/ZD901 by using DMM diode mode, 0.6xxv and OL when reversed.

 

[mbz]

The protection circuit has a simple(RC) timer C901, R902 to provide a mute period, yeah 5 seconds mute sounds about right. During the mute period Q901 will be off so voltages at the relay coil will be the same and >12V (since no current flow/volt drop) 15.9V sounds good. When C901 charges up then Q901 turns on providing a current path through the relay to GND. Relay coil voltages drop to 12.3V is again good.

Current through R903(220) is 18mA, I would have expected a little higher but it does not sound unreasonable. Could not find the datasheet for the relay to confirm relay current. Thinking some more, I would have liked to see 12V across the relay (so thinking 18mA relay current is too low)

Have you tested D804, maybe it's failing under load?
Q901c at +8.3V is too high
Measure the resistance of the relay coil, ballpark 200ohms? Reverse the probe polarity and remeasure to make sure, possibly you have a near short in the relay coil. Try and find the relay datasheet.

 

[ReisDaddy]

Thank you guys for helping me,

@mbz
Not tested D804 underload yet, how to do that?
Here is the result of the relay coil: 819 ohm



Edit:
Diode mode Red Black = 0.382v
Reverse probe: same 0.382v

And cannot find datasheet everywhere in internet.

 

[mbz]

I screwed up the math on the relay current, should be (12.3V-8.3V)/(819+220)=3.8mA (low?)
My main concern is that Q901c should at/near 0Vdc (Vce sat) and the 12V should be mostly across the relay coil.
Problem might be too low relay current caused by???

Not tested D804 underload yet, how to do that?

Wait at least 5 seconds (mute time) after power on. Measure dc voltage at D804 anode. Repeat for D804 cathode. Has C826 (33uf/25V) been replaced.

Have you replaced the power pilot lamp (typically above the ON button), it's on the same supply as the relay

 

[Goldie99]

When power on, the relay coil both pin is 15.9v. After delay around 5 seconds, they both drop to 12.2v
Is it normal?

I'm not sure this is correct - as long as there's no relay current the voltages on both ends of the relay coil will be equal, and 15.9V seems reasonable. As soon as current turns on, after C901 is charged, then the relay coil should have ca. 12V difference between the 2 ends of the coil - so not "they both drop to 12.2V".

It would be worth extending the voltage checks suggested by mbz, and taking a new set of voltages (after the mute period) on the 2 sides of the relay coil, and on Q901(c) - that would also eliminate any chance that the 8.3V seen previously on Q901(c) was maybe 0.3V (?).

 

[sregor]

When power on, the relay coil both pin is 15.9v. After delay around 5 seconds, they both drop to 12.2v
Is it normal?

And in transistor Q901 SC1845 pins:

PIN	Power ON	Delay 5 secs
RELAY RY901
COIL 1	15.9v	12.3v
COIL 2	15.9v	12.2v
Q901 SC1845
E	0.0v	0.0v
C	15.9v	8.3v
B	-1v	0.66v

Collector of Q901 should go all the way down to near zero volts. There is enough base voltage that it should be firing relay, but it is not.
Relay is not relay a protection circuit, but just a time delay on turn on. Also the 15 volts seems kind of low - it could be C826 is open and not filtering the supply enough. Use same value (33uF) as going up in value slows down turn off time. As I think about it, it seems more likely to be the problem.

Edit - see you changed those parts. Double check installation and look for soldering issues or bad tracks or grounds. There is not anything complicated about that circuit.

 

[ivandezande]

Be sure to replace all the garbage caps in the unit.

I've had this issue on two Nikko preamps, I just bypass the relay. It's not worth the headache, I could never get it going.

 

[ReisDaddy]

I screwed up the math on the relay current, should be (12.3V-8.3V)/(819+220)=3.8mA (low?)
My main concern is that Q901c should at/near 0Vdc (Vce sat) and the 12V should be mostly across the relay coil.
Problem might be too low relay current caused by???

Wait at least 5 seconds (mute time) after power on. Measure dc voltage at D804 anode. Repeat for D804 cathode.

D804 under load:

PIN	ON	5 sec
Anode	8.24v	7.19v
Cathode (-)	15.4v	12.38v

Has C826 (33uf/25V) been replaced.

Yes, new panasonic 33uF 50v

Have you replaced the power pilot lamp (typically above the ON button), it's on the same supply as the relay

I did not replaced the lamp. It lid.
Pin 17 (lamp) = 1.6v

I forget to mention that i pull R819 to block power to headphone amp. Is it OK?

 

[ReisDaddy]

Relay is not relay a protection circuit, but just a time delay on turn on.

Ahh i see, thats why in service manual parts list it says "MUTING SECTION"

There is not anything complicated about that circuit.

Yeah i thought that too. But it is complicating me. I mean us!

Be sure to replace all the garbage caps in the unit.

I've had this issue on two Nikko preamps, I just bypass the relay. It's not worth the headache, I could never get it going.

I plan to recap, but i just want to hear it first how it sound paired to my Sansui and Marantz.
Before i spent more and decide what caps, is it worth or not.

 

[sregor]

How good are the ground connections to the 2 boards (preamp and power supply). Thinking that there is poor filtering due to ground issues near the smoothing cap. Try checking for high AC on the +15 supply voltage. Just a shot. don't think 15 volt supply should drop to 12 with small load....

 

[ReisDaddy]

How good are the ground connections to the 2 boards (preamp and power supply). Thinking that there is poor filtering due to ground issues near the smoothing cap. Try checking for high AC on the +15 supply voltage. Just a shot. don't think 15 volt supply should drop to 12 with small load....

Sorry, how to check good ground? Im not that pro. Can you give me more detail how to that?

Is this enough?
Red Probe Pin 19 YEL and Black probe Pin 18 GRY = 14.9vac (same reversed probe)

 

[sregor]

Sorry about lack of clarity. Check resistance to ground from chassis ground to ground end of capacitor C628. Check for AC voltage on +15 DC supply for relay. From here it looks like the AC is not sufficiently filtered and DC voltages seem low, but that is just a guess.

 

[sregor]

Check for continuity along the green "line"

 

[ReisDaddy]

Sorry about lack of clarity. Check resistance to ground from chassis ground to ground end of capacitor C628. Check for AC voltage on +15 DC supply for relay. From here it looks like the AC is not sufficiently filtered and DC voltages seem low, but that is just a guess.

Do you mean C826?

That is 14.9vac in supply AC pin 18 and 19





Is that correct way?

 

[ReisDaddy]

Check for continuity along the green "line"
View attachment 3260230

Yes its beeping.

 

[ReisDaddy]

Just to give information,
If i pull Q901 from circuit,
Using DMM in circuit,
Pin E : Steady 0v
Pin C: Steady 15.4v
Pin B: from 0v then incremental around 20 sec to reach steady 8v.

 

[sregor]

Just to give information,
If i pull Q901 from circuit,
Using DMM in circuit,
Pin E : Steady 0v
Pin C: Steady 15.4v
Pin B: from 0v then incremental around 20 sec to reach steady 8v.

Those seem to be correct.
By measuring ac, I meant one lead on ground, one on the +15 DC line and meter set to AC. Looking for AC ripple which shouldn't be there.
I have run out of ideas for now. Good luck.

 

[p4spooky]

Just to give information,
If i pull Q901 from circuit,
Using DMM in circuit,
Pin E : Steady 0v
Pin C: Steady 15.4v
Pin B: from 0v then incremental around 20 sec to reach steady 8v.

Those voltages are correct. If you have a KSC2383Y or KSC1815Y try these instead of KSC1845. These will have better current handling.