[ellendelen]

Hi there,

I have been having some trouble getting my mp 566 to work. I don't seem to come past point 5 of the test guide. The manual says that the led should stay off when turned on, but in my case it flashes red green, and then green for a little bit. and then nothing happens when I turn the pots. It reads -5.08 dcv between 0v and tp 8, but I also don't see the tube light up, which I suppose should happen when powered on. 

Earlier on I made the mistake of soldering U4 directly to the pcb (stupid I know) So I figured that I might have fried it and ordered a new TCA 0372 dp1 chip, desoldered the other one and replaced it. But the outcome is the same. 

Any tips?

[ellendelen]

I'm sorry, I mean it reads -5.0 at 0v and tp 8, and the tube does slowly gets warm.

I just don't get any AC volts reading or led turning green/red when turning the pots.

I do get a reading of 14.1 AC volts plus leds turning green/red when inserting the signal into the DI input. 

[JPK]

but I also don't see the tube light up
You must be in total darkness to see the tube glowing.

Do you hear the DI relay clicking when you insert a plug into the DI socket?

[ellendelen]

No clicking when inserting the jack. 

[JPK]

Probably Q1 (2N7000) is dead.
This device is sensitive to static electricity and is preferably handled with the body grounded (shoes removed).

[ellendelen]

So I replaced Q1, the relay is clicking now when inserting the jack, so there was definitely something wrong there. 

Only thing that doesn't match up now is the ACV meting with the 1VAC sine at the input of my rack. 
With the gain set to low nd pot 1 turned to max I don't get a green light, when I turn pot 2 to max I do get a green light, but no acv reading. When switching to mid gain with both pots set to max I get a reading of3.8 ACV and when set to high I get 14.1 ACV

So I think there is still something up? Or is it okay to move ahead?

Thanks in advance

[JPK]

Did you measure the input voltage (1VAC) with the source connected to the pre? The input impedance of the pre may load the source and reduce the input voltage when connected.

[ellendelen]

no I measured the input voltage (1VAC) at the XLR pins. Where can I measure it when the source is connected to the pre?

[ellendelen]

(I do have the lunchbox extender)

[JPK]

On the extender it is between pins 8 and 10.
Without an extender you must remove the cover of the XLR plug to get to the contacts.

[Claudio]

Not trying to hijack this thread, but I have a very similar issue. When I measure the 1kHz sine source directly at the XLR plug unconnected, I get 1VAC, but plugging in the XLR and measuring at the extender with the MP566 connected, voltage falls down to 0.086VAC. That’s a drastic change. In my DAW I can’t even push the output any louder than around 0.7VAC.

My LED also flashes when I switch on power, although the test guide says it shouldn’t.

Any clues what the problem(s) might be?

Thanks!

[JPK]

The input impedance of the MP566 is around 1k2.
Which can be low for some sound cards, creating an voltage attenuator. 
Check the output impedance and max level of your sound card (from the specs sheet).

Now going from 1VAC to 0.086VAC seems really too much loading. Make sure the 48V is off, check the cable.
Check with the gain switch set to LOW.

[ellendelen]

So, I measured 1 VAC at pin 8 and 10 on the extender, with the preamp connected, it didn't drop at all compared to measuring just xlr pins.

Now with gain set to low I turn P1 and it turns green, I turn P2 and it turns red, but I get a reading of 13.3 volts AC instead of 7volts AC. 

[JPK]

Check the value (by color code) and solder joints of R38 to R44.
Are you sure your meter is OK, with a fresh battery?

[Claudio]

Check the output impedance and max level of your sound card (from the specs sheet).

Unfortunately I couldn’t seem to find any info on the output impedance of the interface in my test setup, but it’s a MOTU 4Pre, and I doubt it comes with any unusual specs.

Make sure the 48V is off, check the cable.

Check with the gain switch set to LOW.

Yes, 48V is off and gain switch is set to LOW.

Any other ideas?

Thanks,
Claudio

[JPK]

What DC resistance do you measure between pins 8 & 10 on the extender, with the gain switch on LOW (module powered).
Do you see any resistance between pin 8 and pin 5 (0V).
Do you see any resistance between pin 10 and pin 5 (0V).

[ellendelen]

Check the value (by color code) and solder joints of R38 to R44.
Are you sure your meter is OK, with a fresh battery?

Checked the values, checked the joints, reflowed some of them. Checked the battery of my DDM, which is good. I still get a reading of around 13V with the gain switch set to low and the pots turned fully open. Switched to mid it reads about 15v and switched to high it reads about 10v, which seems odd. 

[JPK]

Try to follow the signal as shown here.

[ellendelen]

I've bought a 'better' multimeter just to be sure. 

With a 0.5 VAC sine I get:

-  ' Set Pot IN to 10, Pot OUT to 0, Gain switch to MID:you should read 3VAC on TP1'  

I get  3.14VAC on TP 1

-  'Set Pot IN to 10, Pot OUT to 10, Gain switch to LOW:you should read 2.25VAC on TP3 and 7.2VAC on TP4.'

I get 2.32VAC on TP3 and 7.5VAC on TP4

[JPK]

it looks like you are all good!

[ellendelen]

Yes! I tested it with a dynamic mic and it sounds awesome, thank you for your help so far!

One minor issue I now have is, the phantom power is not working.. I'll start a new topic concerning this for future reference. 

Thanks!