Author Topic: CP4500 went dark during setup part 6

February 03, 2021, 03:57:34 pm
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Dolbah

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Greetings
My CP4500 went dark during setup part 6 (Calibration).

It powered it on, and the In button worked and the VU meter had light (the needle popped up to 20dB).
I got correct measurments during the voltage check, and everything seemed fine.
But after i had adjustet the sinewave to 3VAC by measuring pin 2/3 on the output XLR the LED went from green to dim orange when i turned it on. I turned it off and back on and now both the VU meter anbd the led is dark.

I have taken the unit out and put it back in several time, with no luck. I have also done a visual check, but nothing seemes off. 
I have also remeasured  0v against V-, V+ , -12v and +12v and i still get the correct measurments.
Audio passes through, but nothing seems to work.

Any one got any suggestion?
« Last Edit: February 03, 2021, 11:42:30 pm by Dolbah »

February 03, 2021, 04:13:49 pm
Reply #1

JPK

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Remove all the IC's for their safety.
First things to check :
https://www.soundskulptor.com/forum/index.php?topic=11.msg11#msg11

Reversed D19, D20 diodes?
Reversed relays?
R104, R105 value?
Solder bridges on CN2a/CN2b connectors.

Check the LED with a DMM
JPK

February 03, 2021, 05:45:44 pm
Reply #2

Dolbah

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Remove all the IC's for their safety. - Done!


  • Forgotten solder joint - No
  • Bad solder joint (reflow suspicious joints), Found 1 :)
  • Reversed components (electrolytics, tatalum's, diodes, transistors, IC's). In case of IC's, probably destroyed, better replace - No, everything is where it is supposed to.
  • Components in the wrong place like IC's or transistors - No, all good.
  • Trim all the component leads and test pins as short as possible. Nothing must touch the chassis plate - Nothing has ever touched the chassis


Reversed D19, D20 diodes? - No
Reversed relays? - No
R104, R105 value? 220
Solder bridges on CN2a/CN2b connectors. 

I did screw up and soldered the CNs wrong way. de-soldering and re-soldering these did wear a bit on the surface of the PCB, revealing some copper curcits. I do get measurments between some pins, but there's no bridges.

In the picture below, there is a connection between the two pins that resides all the way to the left.







Check the LED with a DMM - I must do this later
« Last Edit: February 03, 2021, 11:43:09 pm by Dolbah »

February 03, 2021, 07:48:23 pm
Reply #3

Dolbah

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Update:  I forgot to mention, that i plugged it back in after the last round, and i still did not work. I also tried sending a drumloop through it, to see if it reacts to any of the front panels parameters, but the audio is unaffected, so this is more then just the lights going out. The unit is just not turning on.

Very weird that it worked fine and just suddenly crashed.  No funny smells or visuly broken components either.

One thing i can mention though, is that the "IN" switch was a bit slow in the begining. It did not work every time, i often had to push it a couple of times before it reacted. But suddenly it worked, and now it "clicks" everytime.

February 03, 2021, 09:09:17 pm
Reply #4

Dolbah

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LED test:

The LED is dead, no reaction. I tested another type of new led that i have laying around, just to mtest (since i have not tested LEDs before :) ) and that one worked fine.

Also, did a new sweep of ALL components and checked that every item is the correct one in the correct position. I checked all colorcodes on resistors, each capacitor and so on. I found no mistakes.

I also started reflowing less suspicious solderjoints

EDIT: I also tried to put it in another slot on my Box. Just in case, but same result.

Re-assembled and did a quick test, but still no life.
« Last Edit: February 03, 2021, 11:41:51 pm by Dolbah »

February 04, 2021, 02:21:55 pm
Reply #5

Dolbah

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New day, new tests.

I have gone over every solderjoint, and reflowed almost everyone on PCBA and PCBC

Then I startet measuring connection between components based on the schematics.
Schematics is not my second language, but I  understand most of what I see pretty well.

What I am missing is a overview over which PIN on all CNs are connected to what component?
The Blue/Green dots only refere to what CN but not which PIN on the CN.

I have measured my way to the top PINs on CN2A succesfully from C56.
My question is if there is supposed to be a connection between these two PINS at the top or not?






February 04, 2021, 03:44:34 pm
Reply #6

JPK

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Look at the attached pic that shows the pins interconnect and connections.
Check that you get the correct signals on each pin. You might have destroyed some vias when removing the connector.
JPK

February 04, 2021, 04:12:45 pm
Reply #7

Dolbah

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Look at the attached pic that shows the pins interconnect and connections.
Check that you get the correct signals on each pin. You might have destroyed some vias when removing the connector.
Thanks!

I checked now, and i get the exact same connections as shown in your picture, and no connection between "Vu" and "0V to Vu+"


Could you send me a similar overview of connections / interconnection on the two other CNs? These are the only components i misplaced in the process, so i would like to check their integrity.

Any more tips to get me further are welcome, also i need a new LED, can i get that from you or do i have to locate the part myself?


« Last Edit: February 04, 2021, 05:03:54 pm by Dolbah »

February 05, 2021, 05:21:50 pm
Reply #8

JPK

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The green LED is needed to power up the unit so you need to replace it or short it temporarily.
As you can see on the schematic page 3, the on/off switch activates the bypass relay via the green LED, the meter LEDs and R104.
You can check if there is unusual current through R104 (suspicion due to the LED turning red) by measuring the voltage across it: 1.6V
JPK

February 05, 2021, 06:22:39 pm
Reply #9

Dolbah

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Thanks! I am out of town until tomorrow, but will check asap.

I can insert an other type of led in the meantime.
I have a bunch of those square 2x3mm ones, often used in Euroack etc. That should work temporary, right?

February 06, 2021, 08:30:59 am
Reply #10

JPK

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February 06, 2021, 09:58:16 pm
Reply #11

Dolbah

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Ok, good news is that the unit works again, with new LED (or at least it turns on)

All ICs are still not plugged back in.

I register that again, the VU needle jumps to over 20dB (100% peak) as soon as it turns on, is this because it is not calibrated yet, or is this a symptom?

Voltage across R104 is only 1.1V , is this the/a problem?

Not sure if i dare continue on the setup/calibration yet, until i can get a yay or nay on the R104 voltage




Edit: I tried turning the unit on/off a couple of times and it took not a long time until the new led burned out. So, i'll defo wait until you evaluation of the R104 voltage, and where to go next.






Edit2: I have measured and checked all resistors yet again.
These are the only deviant measurements I get:


I have also measured the Voltage the LED receives, but measuring both LED Pins while the unit is ON. I get a reading of 5.4VDC





Also, please give me an overview of the CN1a and CN3a PINs like you did with CN2a so I can check them



« Last Edit: February 07, 2021, 07:06:30 pm by Dolbah »

February 07, 2021, 11:12:05 pm
Reply #12

Dolbah

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Ok, i don't have the patience to wait anymore.  The led has been out for a while, but the VU and the unit still turns on.
So i plunged in to it and installed the ICs.

First i did some measurments.
All steps 1-4 from your pinned post checked out.
Except:
I measured around +16.4V between 16+ and 0V and -16,4V between -16v and 0V

I also checked the
 Voltage between the LED pins when the unit is on, and measured around 5,7 VDC

I started calibration, and the threshold now reacts, so does makup and dry/wet.

But, when i am supposed to trim the VU meter, it does not work. 
As soon as the unit is on, the VU meter peaks to 100% and nothing changes this.
Not even the T4 "meter-adjust" or any of the front panel controls.

There are no shorts between any of the meter wires.

So, lets just recap where i am now:

1. The LED burns out
2. The VU meter peaks at 100% (needle all the way to the right)
3. I have measured 5,7 VDC between the LED pins, this should be the current voltage going through, right?
4. Voltage across R104 is only 1.1V
5. The T1 adjuster does not work on the VU, the needle position is always far right.
6. I measure sligtly to much Voltage on 0V against +/-16V test pins


So, is it to much voltage that peaks the VU and Burns the LED at the same time?

February 08, 2021, 11:07:40 am
Reply #13

JPK

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You have too much current in the LED. The current is limited by R104, RLY1, Meter LED.
- Keep the IC's removed until this is sorted out.
- Check the meter: 600 ohms between the large terminals, infinite resistance between any other terminals.
- Check the relay coil, 2800 ohms across D19.
- Look for a short circuit between the CN2 Vu- pin (second down-left)and any other close pin.
JPK

February 08, 2021, 11:36:47 am
Reply #14

Dolbah

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- Keep the IC's removed until this is sorted out.  Done!

- Check the meter: 600 ohms between the large terminals, infinite resistance between any other terminals.
569 Ohm, on large terminals  and only "1" (infinite, right?) between the small ones



- Check the relay coil, 2800 ohms across D19.  Measuring 2.83 at 20k on the DDM


- Look for a short circuit between the CN2 Vu- pin (second down-left)and any other close pin.

If PCBa is disconnected i do not get a measurment.
If PCBa is connected tom PCBc, i measure 0,54  (20k on DDM) with the second down right pin. Se picture below. 

Edit: I get no measurment between the corresponding pins on CN2b 

« Last Edit: February 08, 2021, 12:20:13 pm by Dolbah »

February 08, 2021, 12:19:23 pm
Reply #15

JPK

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Quote
569 Ohm, on large terminals  and only "1" (infinite, right?) between the small ones
You must also check between the small and large terminals, in case there is a short circuit inside the meter.





JPK

February 08, 2021, 12:21:51 pm
Reply #16

Dolbah

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Quote
569 Ohm, on large terminals  and only "1" (infinite, right?) between the small ones
You must also check between the small and large terminals, in case there is a short circuit inside the meter.
I have checked this, there are no shorts between any of the meter wires.

February 08, 2021, 01:06:40 pm
Reply #17

Dolbah

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If PCBa is disconnected i do not get a measurment.
If PCBa is connected tom PCBc, i measure 0,54  (20k on DDM) with the second down right pin. Se picture below.

Edit: I get no measurment between the corresponding pins on CN2b

So, i am looking at these.  As next suspects.

First, this is how i have been thaught to measure shorts:

I set the DDM to Ohm and 200. I measure my probes togheter and get something around 00,7
I then touch the probes between any suspected shorts on the PCB (where there should be no connection at all) And if i get a similar measurment i conclude there is a short.

Is this the correct way in your eyes?

I get no shorts between the VU+ and VU- pin on CN2a/b this way.

If i choose to increase sensitivity to 20M, i do not get a reeading between probes anymore, but now i get a reading between VU+ and VU- pins on CN2a, without PCBc connected on 0,25

Forgive my lack of experience on this specific measure, but is this a sign of short-circuit?

The visuals indicates no short at all, so i am uncartain why the 20M gives me a reading.
Here are some closeups of the VU pins










February 08, 2021, 02:39:44 pm
Reply #18

JPK

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Quote
Is this the correct way in your eyes?
Yes you are correct.


Quote
If i choose to increase sensitivity to 20M, i do not get a reeading between probes anymore, but now i get a reading between VU+ and VU- pins on CN2a, without PCBc connected on 0,25
This is not a short circuit.


Can you temporarily replace the LED by a resistor of 1 to 1.5 k ?
And check if you can hear the relay clicking when you activate the compressor.
JPK

February 08, 2021, 02:49:10 pm
Reply #19

Dolbah

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Can you temporarily replace the LED by a resistor of 1 to 1.5 k ?
And check if you can hear the relay clicking when you activate the compressor.
No, i do not have any spare Resistors around. i would have to de-solder one from PCBb in that case

Edit: But, why not. I'll just borrow one from PCBb. I'll take R72
« Last Edit: February 08, 2021, 02:57:09 pm by Dolbah »

February 08, 2021, 03:18:23 pm
Reply #20

Dolbah

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Can you temporarily replace the LED by a resistor of 1 to 1.5 k ?
And check if you can hear the relay clicking when you activate the compressor.
No, i do not have any spare Resistors around. i would have to de-solder one from PCBb in that case

Edit: But, why not. I'll just borrow one from PCBb. I'll take R72
I put R72 (1K5)  in the LED spot, and yes the Relay clicks whn turning the unit on.

Also, for the first time ever, the VU needle is resting at 0db ;D

But, the resistor is taking down the exessive voltage, right? So we still need to find out where the extra voltage is coming from.

February 08, 2021, 04:01:28 pm
Reply #21

JPK

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What DC voltage across the 1k5?
What DC voltage across the meter small terminals?
What DC voltage across the relay (taken across D19)?
What DC voltage across R104?
Does the meter lights up?








JPK

February 08, 2021, 05:05:55 pm
Reply #22

Dolbah

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What DC voltage across the 1k5?
What DC voltage across the meter small terminals?
What DC voltage across the relay (taken across D19)?
What DC voltage across R104?
Does the meter lights up?
What DC voltage across the 1k5?  8,6 VDC
What DC voltage across the meter small terminals?  5,7 VDC
What DC voltage across the relay (taken across D19)?  16,8 VDC
What DC voltage across R104? 1,3 VDC
Does the meter lights up? Yes

February 08, 2021, 06:52:18 pm
Reply #23

JPK

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This looks plain normal!
Nothing happens if you shake the wires to the meter a little?
I just cannot understand how the green LED may have burnt. And why the needle went to 20.
I suspected an intermittent short circuit inside the meter.
JPK

February 08, 2021, 07:06:59 pm
Reply #24

Dolbah

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This looks plain normal!
Nothing happens if you shake the wires to the meter a little?
I just cannot understand how the green LED may have burnt. And why the needle went to 20.
I suspected an intermittent short circuit inside the meter.
Hmm..
I'll have to shke the wires later, but i have done this allready.

But does not the 1K5 resistor we borrowed affect stuff in a positive direction? or are you saying that the LED should "resist" the equivalent of 1K5?

Are you now saying that there is not coming too much current into the LED/meter at all, even if i remove the resistor and put in a new LED or a short?

Can i safely put in the ICs and test?

Ok, lets assume the original LED was just bad. (Please send me the specs, so i can order a new one)

What if i remove the resistor, and try to insert a new (temporary) LED again. Lets just investigate their specs:

These are the ones i have available.
I tried the White one last time. It burned out, but kept the connection intact.

https://www.switchelectronics.co.uk/pure-white-3-x-2mm-rectangular-led-500mcd-100

Are there any reasone any of these LEDs wont be suitable?
« Last Edit: February 08, 2021, 08:35:00 pm by Dolbah »