[narekm97]

Hello, 

When I connected my MP566 to my lunchbox, I turned on the power and got a red light on the LED. After around 5 seconds the LED light went out and I couldn't get any signal through the preamp. Not sure where to look for the problem 

[JPK]

Check again the voltages then follow these tests: https://www.soundskulptor.com/forum/index.php?topic=209.msg981#msg981

[heimito]

I have the very same problem as described above.

I also checked Topic: "In case your MP566 doesn't work as expected" - there are no "usual suspect" to be found on my build.

Neither the DI nor the Mic in let any signal through.

What should I do?

[JPK]

Try to follow the signal as described in the same place here.
It will tell you where to look.

[heimito]

Thank you for replying.

I was not able to follow the instructions to "follow the signal" - I am new to this DIY stuff and I simply don't know what to do with the instructions.

Since this is my first build, I might have done something wrong, although I took special care to insert all the components in the right direction.

This is what happenes:
- I turn on the power of my R6, the LED flashes red for about a secont or two then it goes out
- the device emitts a faint smell, so I think some components are heating, the tube is not getting warm and the tube does not light up

Here is, what the test-restults are:

Test 1 (Short circuit test) -> 2,72 MOhms (If I got the test right, since there is no GND test pin on my board)

Test 2 (High Voltage Test) -> 0,03V and decreasing over time to 0

Test 3 (Low Voltage Test) -> -0,02 and rising to 0

Test 4 (Signal Check) -> I read 1,63V between OV and TP4, the LED stays off even if I max out the Output potentiometer

If you know what that means; I would be greatful to get any advice how to find and fix the problem.

[JPK]

There is something wrong around U4, D14, D15, R47...R50.
Check value, direction and solder joints.

[heimito]

Thank you. I checked the components you told me:

U4 - direction ok, solder joints ok

D14 - direction ok, solder joints ok

D15 - direction ok, solder joints ok

R47 - 330k - ORG-ORG- BLK- ORG-BRN measures at 105 kOhm

R48,49,50 - 47k - YEL-VIO-BLK-RED-BRN measure at 41kOhm

So there is one difference in R47... is that the problem?

[JPK]

From the picture I can see that you have the wrong IC in U4 (OPA134 instead of L272/TCA0372).
The OPA134 goes in U1.

[heimito]

Thank you. I switched the ICs and now it tests as follows:

Test 2 (High Voltage Test) -> 223,7V

Test 3 (Low Voltage Test) -> 0,0 V

Test 4 (Signal Check) -> LED stays off all the time. I measure 0,003 VAC with in and out turned on to max.

Where else can i look for problems?

[JPK]

You have probably destroyed the TCA0372 by putting it in the wrong spot. Maybe both IC's.

[heimito]

Thanks for your help.

I replaced both ICs - but nothing changed. It still does not work.

Test 1 (Short circuit test) -> 2,72 MOhms

Test 2 (High Voltage Test) -> 223,8V

Test 3 (Low Voltage Test) -> -0,04 and rising to 0

Test 4 (Signal Check) -> LED stays off all the time. I measure 0,003 VAC with in and out turned on to max.

What could it be?

[JPK]

The heater is not working.
Check the tube heater by measuring the resistance value between TP8 and V- (with power off): ~12 ohms.
If you don't get this value, check on the tube itself between pins 4 and 5 (bottom view).

[heimito]

I measure:

between TP8 and V- => 12,3 ohm - Sometimes wildly jumping up to 15 to 20 Ohms

between pin 4 and 5 of the Tube (bottom view): 16 ohms and rising

between pin 5 & 6 (bottom view): 12,2 Ohms

[JPK]

between pin 5 & 6 (bottom view): 12,2 Ohms
Do you confirm. This is totally uncorrect.
Can you check again the tube when disconnected?

[heimito]

You are right. I was off by one pin.

I measured again with the tube disconnected: 127,5 Ohms.

Do I need a new tube?

[JPK]

Is that between pins 4 and 6 (not sure from the photo).
If true, then you need to replace the tube. Contact us here.

[heimito]

Thank you - I replaced the tube, now audio is coming through. But very very quiet.

The sound is not distorted or anything, but very quiet.

Here is what I did:

I set the Input Level on my apollo twin to 3/4 (that is 52dB)
I set the MP566 Input to 10 and output to 10

With the Gain Switch to low: I receive 46dB of level
With the Gain Switch to mid I receive 20dB of level
With the Gain Switch to hi: I receive 36dB of level (yes, acutally quieter than with mid)

Still seems something to be wrong. What else could I do?

[JPK]

Try sending the signal via the DI jack and check if it is louder?
Try to follow the signal

[heimito]

I re-checked:

Audio-Check:
POT in & POT out set to 10
Apollo Twin set to 65 dB input (fully turned up) - Noise is at 46dB constant

Code: [Select]

Line-in:     |  High-Z in:
Lo:  -27 dB  |  Lo:  -18 dB
Mid:  -5 dB  |  Mid: -18 dB
Hi:  -25 dB  |  Hi:  -36 dB

Then I followed the signal. I sent the 1000Hz sine to the line-in, measuring 0,5V between 8 and 10 of the extender

Code: [Select]

    | black probe | red probe
------------------------------
TP1 |  0,142 V    |  0,207 V
TP3 |  0,137 V    |  0,217 V
TP4 |  0,164 V    |  0,227 V

[JPK]

    | black probe | red probe
------------------------------
TP1 |  0,142 V    |  0,207 V

The value on TP1, TP3, TP4 are measured against 0V (black probe on the 0V test pin).
The value on TP1 should be around 3VAC with the gain switch on MID.
Do you get a better level when sending the signal on the DI input?

[heimito]

Thank you for clarifying.
I remeasured: black probe to oV - red probe to TP1, TP3, TP4.

Code: [Select]

    | Line-in |  DI in
-----------------------
TP1 |  0,0V   | 0,496V
TP3 |  0,0V   | 0,0V
TP4 |  0,0V   | 0,0V
Same results for Gain Switch lo, mid and hi
Potentiometers did not affect the measurement

I got 0,496V on pin 8 and 10 of the extender - my multimeter showed 1,044kHz - so the input should be right.

[JPK]

You have 2 issues here.
- The input signal not reaching the first triode: Check the connections on RLY1, transformer T1, potentiometer P1.
- The tube amp gives no output: Check the connections on the tube, on potentiometer P2.

Check the usual suspects.

[heimito]

I checked all the connections. Solder joints look okay to me, only T1 looks a bit strange.

I remember having trouble soldering the 90° connectors of the tube PCB (A) to the Main PCB. The solder just didnt stick correctly.

Please find attached pictures of the joints.

Should I resolder?


RLY1


T1


P1


Tube socket


PCB Connector


P2

[JPK]

This solder joint on T1 looks bad:



Should I resolder?
Do not hesitate to reflow any suspect joint. Your iron should be hot enough, around 320-350°C.

[heimito]

I finally got the time, to resolder and do the tests again.

The signal is now coming through louder
- Pot IN and Pot OUT turned to max
- input level on my apollo is turned to max (65dB)
- Signal is louder but only in position mid gain (solid level up to 0dB)
- but Signal is very very noisy.

Test 4 (low voltage check) -> -15V

Test 5 (signal check)

Code: [Select]

    |          Line In         |/|           DI In          |
    |   Lo   |   Mid  |   Hi   |/|   Lo   |   Mid  |   Hi   |
----|--------|--------|--------|/|--------|--------|--------|
TP1 | 0,271V | 3,043V | 3,043V |/| 0,496V | 0,496V | 0,496V |
TP3 | 0,000V | 0,006V | 0,000V |/| 0,000V | 0,000V | 0,000V |
TP4 | 0,001V | 0,019V | 0,001V |/| 0,002V | 0,002V | 0,000V |
What else should I try?