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Nikko ALpha III

philster said:
Nothing changed except my -56vdc jumped to -80vdc. I shut it dow. Yes i did back off the bias before going full mains. You think the 1.2vdc on the left output will keep it from engaging?
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Just to clarify, where exactly did you measure the -80 VDC?

Also, was that 1.2 VDC measured at the amplifier output, before the protection relay? If so, that's definitely abnormal and could be enough to prevent the relay from engaging.

EchoWars discussed DC offset and protection thresholds in this thread:
https://audiokarma.org/forums/threads/amplifier-distortion-dc-offset-and-you.5634/
 
EchoForge said:
Just to clarify, where exactly did you measure the -80 VDC?

Also, was that 1.2 VDC measured at the amplifier output, before the protection relay? If so, that's definitely abnormal and could be enough to prevent the relay from engaging.

EchoWars discussed DC offset and protection thresholds in this thread:
https://audiokarma.org/forums/threads/amplifier-distortion-dc-offset-and-you.5634/
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-80vdc at pin 17 on the main amplifier board. Should be -56vdc. I measured at the output of the main amp board which is pin 12 and that connects to pins 10 and 11 on the reg/protect board. I assume you have the schematic?
 
Yes, I have the schematic. It shows approximately ±80 V unregulated and ±57 V regulated. Pin 17 should be around -57 V, not -80 V. It looks like your negative regulator isn't regulating properly, and the DBT may have been masking the problem by lowering the unregulated supply voltage. I'd investigate Q816 and its control circuit first.
 
Thanks, I will investigate tomorrow. Tired and my eyes are shot as I have been after all day and I don't want to make a mistake
 
EchoForge said:
Yes, I have the schematic. It shows approximately ±80 V unregulated and ±57 V regulated. Pin 17 should be around -57 V, not -80 V. It looks like your negative regulator isn't regulating properly, and the DBT may have been masking the problem by lowering the unregulated supply voltage. I'd investigate Q816 and its control circuit first.
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Back at it. I got both regulators at +/- 63vdc. . Voltage at the main board however is +53vdc at pin 4 and -61vdc at pin 17. and we are connected to the DBT. Still too much current being drawn on the neg rail. I have replaced the regulator with the original pulling out the MJE15033
 
Ugh, I installed Q815 backwards, sigh. That changes everything. I get a steady +/- 61vdc at both pins but still have my 1.2vdc on one of the outputs. Its on the left channel output and that could explain why the outputs are getting warm. The other outputs are nice and cool.
 
There still has to be an issue with the regulator. I should be getting 57vdc to the main board and I am not even close. I have replaced both q815 and 816 no change
 
Before we go any further, let's make sure we're both looking at the same service manual and identifying the same measurement points.

On the schematic, do you see the regulator/protection board outlined by the dashed lines?

If we're looking at the same schematic, let's start by checking the power supply section before moving on to the amplifier boards.

Could you take the following DC voltage measurements directly on the Regulator/Protection board, using pin 16 as your ground reference?
  • Pin 15: Positive unregulated supply (+80 V)
  • Pin 17: Negative unregulated supply (-80 V)
  • Pin 6: Positive regulated output (+57 V)
  • Pin 18: Negative regulated output (-57 V)
Also, could you measure the voltage directly across ZD815 and ZD816, the two 22 V Zener diodes?

Please keep the DBT connected and take all six readings under the same conditions.

Since Q815 was previously installed backwards, I'd like to establish whether both regulators are actually functioning correctly before we investigate the amplifier circuits.

One more thing: what wattage bulb are you using in your DBT?

1794101977253.png1794102009206.png
 
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EchoForge said:
Before we go any further, let's make sure we're both looking at the same service manual and identifying the same measurement points.

On the schematic, do you see the regulator/protection board outlined by the dashed lines?

If we're looking at the same schematic, let's start by checking the power supply section before moving on to the amplifier boards.

Could you take the following DC voltage measurements directly on the Regulator/Protection board, using pin 16 as your ground reference?
  • Pin 15: Positive unregulated supply (+80 V)
  • Pin 17: Negative unregulated supply (-80 V)
  • Pin 6: Positive regulated output (+57 V)
  • Pin 18: Negative regulated output (-57 V)
Also, could you measure the voltage directly across ZD815 and ZD816, the two 22 V Zener diodes?

Please keep the DBT connected and take all six readings under the same conditions.

Since Q815 was previously installed backwards, I'd like to establish whether both regulators are actually functioning correctly before we investigate the amplifier circuits.

One more thing: what wattage bulb are you using in your DBT?

View attachment 3871799View attachment 3871803
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Sorry I had shopping to do. We are on the same page as the schematic. We are taking measurements from the same locations.
pin 15 61vdc
pin 17 -61vdc
pin 6 61vdc
pin 18 -61vdc

ZD815 22.1 vdc
zd816 21.3 vdc

I have a 75w bulb in there as it was the only incandescent bulb I could find. I know if I were to go full mains I would have 80vdc unregulated and 80vdc regulated. There doesnt seem to be any regulation. Before I changed out the differential I was able to get to relay engaged and had bias readings along with offset voltage.
 
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philster said:
Sorry I had shopping to do. We are on the same page as the schematic. We are taking measurements from the same locations.
pin 15 61vdc
pin 17 -61vdc
pin 6 61vdc
pin 18 -61vdc

ZD815 22.1 vdc
zd816 21.3 vdc

I have a 75w bulb in there as it was the only incandescent bulb I could find. I know if I were to go full mains I would have 80vdc unregulated and 80vdc regulated. There doesnt seem to be any regulation. Before I changed out the differential I was able to get to relay engaged and had bias readings along with offset voltage.
Click to expand...
I noticed you corrected the DBT bulb wattage from 100 W to 75 W in your previous post.

Have you been using the same 75 W bulb since the beginning of this repair, including when you measured ±56 V at the amplifier boards in post #16?

Are you still using that same bulb, or have you been switching between different wattages during troubleshooting?

I'm asking because the bulb wattage can significantly affect the voltage reaching the regulators, which is important when comparing your earlier readings with the current ones.
 
EchoForge said:
I noticed you corrected the DBT bulb wattage from 100 W to 75 W in your previous post.

Have you been using the same 75 W bulb since the beginning of this repair, including when you measured ±56 V at the amplifier boards in post #16?

Are you still using that same bulb, or have you been switching between different wattages during troubleshooting?

I'm asking because the bulb wattage can significantly affect the voltage reaching the regulators, which is important when comparing your earlier readings with the current ones.
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same bulb, just a typo i made
 
If philster in forum DIY is you... I went back through your 2024 Nikko Alpha III repair thread on DIYAudio, where Mooly helped you troubleshoot the voltage regulators. There's some useful information there that applies directly to what we're seeing now.

In post #22, Mooly explained how the Zener reference and the 33k/22k resistor divider determine the regulated output voltage.

Using your current Zener readings:
  • ZD815: 22.1 V → approximately +56.8 V regulated
  • ZD816: 21.3 V → approximately -54.8 V regulated
These are the approximate voltages we should expect if both regulators are operating normally.

Nikko Alpha III that I can't set the idle current on

More importantly, in post #35, Mooly explained that the regulators should maintain approximately ±56 V with around ±65 V or more at their inputs.

And in your own post #43, on November 6, 2024, you reported approximately ±66 V at the collectors of Q815 and Q816, with around ±55 V at their emitters. So you had both regulators working properly under the DBT on that Alpha III.

Nikko Alpha III that I can't set the idle current on

Now, on your current Alpha III, we're seeing only ±61 V at the regulator inputs, with the outputs following at the same voltage.

With the 75 W bulb limiting the incoming supply, we may simply not have enough voltage for the regulators to operate properly.

I'd like to establish whether we're dealing with insufficient input voltage under the DBT or an actual regulator fault before replacing any more components.

If philster in forum DIY is you, did you happen to record what wattage bulb you were using in your DBT during that 2024 repair? Have you been using the same bulb ever since, or have you changed wattages over the years?

That would be useful to know, especially since you were able to get both regulators working at approximately ±55 V with ±66 V at their inputs back then.
 
EchoForge said:
If philster in forum DIY is you... I went back through your 2024 Nikko Alpha III repair thread on DIYAudio, where Mooly helped you troubleshoot the voltage regulators. There's some useful information there that applies directly to what we're seeing now.

In post #22, Mooly explained how the Zener reference and the 33k/22k resistor divider determine the regulated output voltage.

Using your current Zener readings:
  • ZD815: 22.1 V → approximately +56.8 V regulated
  • ZD816: 21.3 V → approximately -54.8 V regulated
These are the approximate voltages we should expect if both regulators are operating normally.

Nikko Alpha III that I can't set the idle current on

More importantly, in post #35, Mooly explained that the regulators should maintain approximately ±56 V with around ±65 V or more at their inputs.

And in your own post #43, on November 6, 2024, you reported approximately ±66 V at the collectors of Q815 and Q816, with around ±55 V at their emitters. So you had both regulators working properly under the DBT on that Alpha III.

Nikko Alpha III that I can't set the idle current on

Now, on your current Alpha III, we're seeing only ±61 V at the regulator inputs, with the outputs following at the same voltage.

With the 75 W bulb limiting the incoming supply, we may simply not have enough voltage for the regulators to operate properly.

I'd like to establish whether we're dealing with insufficient input voltage under the DBT or an actual regulator fault before replacing any more components.

If philster in forum DIY is you, did you happen to record what wattage bulb you were using in your DBT during that 2024 repair? Have you been using the same bulb ever since, or have you changed wattages over the years?

That would be useful to know, especially since you were able to get both regulators working at approximately ±55 V with ±66 V at their inputs back then.
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Yes that is me in DIY and that was of course a completely different Alpha III. I am using the same DBT setup with the same bulb intact
 
Finally back in the tech room. I had some personal stuff with my dad and cancer treatment that took priority. So I guess we need to determine if the regulators are actually working?
 
philster said:
Going full mains I get 80vdc on the collector and 80vdc on the emitters of Q815 and Q816
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Before we go any further, I'd like to come back to why I was asking about your DBT bulb wattage.

With the 75 W bulb, you measured approximately ±61 V at both the inputs and outputs of the regulators. When you switched to full mains, those voltages increased to approximately ±80 V, but the outputs still followed the inputs.

There's a useful Audiokarma thread started by EchoWars about selecting the appropriate DBT bulb wattage. I think it's worth reading:
https://audiokarma.org/forums/threads/dim-bulb-tester-what-watt-bulb.330103/

Now, consider what happens when you increase the wattage of the incandescent bulb in a DBT.

How does that affect the voltage reaching the amplifier, and what happens to the current-limiting capability of the DBT?

With that in mind, can you think of a way we could have increased the voltage available to the regulators without going directly to full mains?

And what would you expect to see at the regulator outputs as the input voltage increases, assuming both regulators are working properly?

I'd like us to work through this step by step, using your measurements to understand what's happening in the circuit before making any further changes.

For now, I'd avoid another full-mains test until we've established why the regulator outputs are following their inputs.
 
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EchoForge said:
Before we go any further, I'd like to come back to why I was asking about your DBT bulb wattage.

With the 75 W bulb, you measured approximately ±61 V at both the inputs and outputs of the regulators. When you switched to full mains, those voltages increased to approximately ±80 V, but the outputs still followed the inputs.

There's a useful Audiokarma thread started by EchoWars about selecting the appropriate DBT bulb wattage. I think it's worth reading:
https://audiokarma.org/forums/threads/dim-bulb-tester-what-watt-bulb.330103/

Now, consider what happens when you increase the wattage of the incandescent bulb in a DBT.

How does that affect the voltage reaching the amplifier, and what happens to the current-limiting capability of the DBT?

With that in mind, can you think of a way we could have increased the voltage available to the regulators without going directly to full mains?

And what would you expect to see at the regulator outputs as the input voltage increases, assuming both regulators are working properly?

I'd like us to work through this step by step, using your measurements to understand what's happening in the circuit before making any further changes.

For now, I'd avoid another full-mains test until we've established why the regulator outputs are following their inputs.
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I agree. Its just not making a lot of sense to me and have not changed anything in regards to the DBT. Same DBT and bulb
 
What I was trying to point out is that you can use different bulb wattages in your DBT to change how much current is allowed through and how much voltage reaches the amplifier.

A 100 W bulb will generally allow more voltage to reach the amplifier than a 75 W bulb, while still providing some current limiting. A 150 W bulb would reduce that limitation further.

So instead of going directly from a 75 W DBT to full mains, we could have increased the bulb wattage progressively and observed how the regulator input and output voltages responded.

The trade-off is that increasing the bulb wattage also reduces the protection provided by the DBT.

Now, considering your measurements, what would you expect a properly functioning ±57 V regulator to do as its input voltage increases from ±61 V toward ±80 V?
 
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