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MindPrint Envoice LED issue - Any technician here?
Old 23rd July 2020
  #1
MindPrint Envoice LED issue - Any technician here?

Hello there,

My MindPrint Envoice (MK1) has a weird issue: sound is going thru but I have no leds working for input/output levels.

I recently opened it, and discovered that a resistance had burnt. (probably 10+ years ago, as the piece already had the issue before).

So I've decided to remove the component and to replace it by a brand new one.
When I've tested the preamp, the leds were still not working... and quickly a burning smell catched my nose. I opened the preamp again, and discovered the resistance has burnt again.

As I'm a newbie at this, I think the component burns for a reason. Changing it without identifying the other issue is pointless. Problem is, how to proceed to find the issue on the board?

Better: if anyone already had this issue on the MindPrint Envoice, please share. Thanks.

-

Here are some pictures of the unit.
The resistance burning is the R5.
Attached Thumbnails
MindPrint Envoice LED issue - Any technician here?-mindprint_envoice_fullview.jpg   MindPrint Envoice LED issue - Any technician here?-mindprint_envoice_leds.jpg   MindPrint Envoice LED issue - Any technician here?-mindprint_envoice_leds-plug.jpg   MindPrint Envoice LED issue - Any technician here?-mindprint_envoice_r5-burnt.jpg  
Old 31st July 2020
  #2
Any helper?
Old 1st August 2020
  #3
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Rick Dalton's Avatar
Quote:
Originally Posted by _barnee View Post
Any helper?
Can you get some better pic's of the main PCB? That's most likely where your issue is. See if you can find schematics. You did say you replace the LED board, right?
Old 1st August 2020
  #4
Village Idiot
 
Labs's Avatar
 

Quote:
Originally Posted by _barnee View Post
Hello there,

My MindPrint Envoice (MK1) has a weird issue: sound is going thru but I have no leds working for input/output levels.

I recently opened it, and discovered that a resistance had burnt. (probably 10+ years ago, as the piece already had the issue before).

So I've decided to remove the component and to replace it by a brand new one.
When I've tested the preamp, the leds were still not working... and quickly a burning smell catched my nose. I opened the preamp again, and discovered the resistance has burnt again.

As I'm a newbie at this, I think the component burns for a reason. Changing it without identifying the other issue is pointless. Problem is, how to proceed to find the issue on the board?

Better: if anyone already had this issue on the MindPrint Envoice, please share. Thanks.


Here are some pictures of the unit.
The resistance burning is the R5.
Going purely by visual inspection.

Looks like there are two LED circuits built the same way, on the same chip (BA682A) - it also looks like you have voltage regulation for the meter circuit going on on the right side fo the meter board (small TO92 package on the right).

If you are only having problems on the meter on the left, you are probably drawing too much current through R5 due to a faulty BA682, so the burned resistor you replaced is a symptom, not the culprit.

If you are having problems with both/all meter circuits, its not quite as easy to narrow it down without getting in there with a meter. Might be a wonky regulator or something third or fourth.

Gustav
Old 1st August 2020
  #5
Quote:
Originally Posted by Rick Dalton View Post
Can you get some better pic's of the main PCB? That's most likely where your issue is. See if you can find schematics. You did say you replace the LED board, right?
Hi Rick,

I'll try to get a better picture of the main PCB.
I've already searched for schematics and haven't found anything.
Only the resistance located in R5 has been replaced, not the LED board.
Old 1st August 2020
  #6
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Rick Dalton's Avatar
Quote:
Originally Posted by _barnee View Post
Hi Rick,

I'll try to get a better picture of the main PCB.
I've already searched for schematics and haven't found anything.
Only the resistance located in R5 has been replaced, not the LED board.
R5 , I just noticed, I thought you had replace the board, my bad.
I'd noticed a few issues with these. As barnee mentioned, you need a meter to chase this.
Old 1st August 2020
  #7
Quote:
Originally Posted by Labs View Post
Going purely by visual inspection.

Looks like there are two LED circuits built the same way, on the same chip (BA682A) - it also looks like you have voltage regulation for the meter circuit going on on the right side fo the meter board (small TO92 package on the right).

If you are only having problems on the meter on the left, you are probably drawing too much current through R5 due to a faulty BA682, so the burned resistor you replaced is a symptom, not the culprit.

If you are having problems with both/all meter circuits, its not quite as easy to narrow it down without getting in there with a meter. Might be a wonky regulator or something third or fourth.

Gustav

Hi Gustav,

Many thanks. I'll check the BA682 in the coming days.
how could I test it?
(I have a meter)
Also, I've noticed that the condenser (the dark blue things) show null on the meter... is this ok or should I get a value there?
Old 1st August 2020
  #8
Quote:
Originally Posted by Rick Dalton View Post
R5 , I just noticed, I thought you had replace the board, my bad.
I'd noticed a few issues with these. As barnee mentioned, you need a meter to chase this.
I have a meter, but dont know the method for a good use in a test.
Old 1st August 2020
  #9
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Rick Dalton's Avatar
Quote:
Originally Posted by _barnee View Post
I have a meter, but dont know the method for a good use in a test.
Are you talking about the blue C3? If its bad, that can cause this. put your meter on ohm symbol or continuity or the diode symbol and put your leads on each end and see if the reading climes, if not switch the leads around and try again if the reading doesn't clime, it could be bad. make sure the units unplugged.
Old 1st August 2020
  #10
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Rick Dalton's Avatar
You could look on youtube, how to do a continuity test on a capacitor.
Old 1st August 2020
  #11
Quote:
Originally Posted by Rick Dalton View Post
Are you talking about the blue C3? If its bad, that can cause this. put your meter on ohm symbol or continuity or the diode symbol and put your leads on each end and see if the reading climes, if not switch the leads around and try again if the reading doesn't clime, it could be bad. make sure the units unplugged.
Can't remember about the C3, but the C4, C5, C6 that are located on the right side of the LED board. I'm pretty sure I had 0 screened on the meter when I placed the leads on. Will try again tomorrow as it is past midnight here.

What are those component supposed to do? Lower/control the voltage?
Old 1st August 2020
  #12
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Rick Dalton's Avatar
Quote:
Originally Posted by _barnee View Post
Can't remember about the C3, but the C4, C5, C6 that are located on the right side of the LED board. I'm pretty sure I had 0 screened on the meter when I placed the leads on. Will try again tomorrow as it is past midnight here.

What are those component supposed to do? Lower/control the voltage?
they store and filter voltage, but if your getting 0 , it may be a dead short.
Old 1st August 2020
  #13
Quote:
Originally Posted by Rick Dalton View Post
they store and filter voltage, but if your getting 0 , it may be a dead short.
I'm watching some youtube videos about.

What worries me is if those capacitors are dead, there is a reason for it. Too high voltage in the circuit?
Old 2nd August 2020
  #14
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Rick Dalton's Avatar
Quote:
Originally Posted by _barnee View Post
I'm watching some youtube videos about.

What worries me is if those capacitors are dead, there is a reason for it. Too high voltage in the circuit?
no they usually dead of old age. They dry up.
Old 2nd August 2020
  #15
Village Idiot
 
Labs's Avatar
 

Quote:
Originally Posted by _barnee View Post
Hi Gustav,

Many thanks. I'll check the BA682 in the coming days.
how could I test it?
(I have a meter)
Also, I've noticed that the condenser (the dark blue things) show null on the meter... is this ok or should I get a value there?
Youll have a hard time measuring resistance across a capacitor specifically, and its impossible to measure components values in general.

You did not answer, wether this was happening with both meter circuits/all the LEDs. If not, I would try to narrow it down to the BA682.

Caps look fine, they can dry up and short out with old age, but I doubt they are the cause of problems here.

Gustav
Old 4th August 2020
  #16
Quote:
Originally Posted by Labs View Post
Youll have a hard time measuring resistance across a capacitor specifically, and its impossible to measure components values in general.

You did not answer, wether this was happening with both meter circuits/all the LEDs. If not, I would try to narrow it down to the BA682.

Caps look fine, they can dry up and short out with old age, but I doubt they are the cause of problems here.

Gustav
OK for the caps. Thanks.

Last time i did a test, the compressor LEDs (on the right side of the front panel of the unit) was working. Only the input/output LEDs were not.

I've re-opened the box and did some pictures today.
More to follow.
Old 4th August 2020
  #17
Large view.
Attached Thumbnails
MindPrint Envoice LED issue - Any technician here?-img_5008.jpg  
Old 4th August 2020
  #18
Caps from the LED PCB.
Attached Thumbnails
MindPrint Envoice LED issue - Any technician here?-img_5010.jpg   MindPrint Envoice LED issue - Any technician here?-img_5009.jpg   MindPrint Envoice LED issue - Any technician here?-img_5012.jpg   MindPrint Envoice LED issue - Any technician here?-img_5013.jpg   MindPrint Envoice LED issue - Any technician here?-img_5014.jpg  

MindPrint Envoice LED issue - Any technician here?-img_5011.jpg  
Old 4th August 2020
  #19
The circuit on the back LED PCB.
Attached Thumbnails
MindPrint Envoice LED issue - Any technician here?-img_5024.jpg   MindPrint Envoice LED issue - Any technician here?-img_5026.jpg   MindPrint Envoice LED issue - Any technician here?-img_5028.jpg   MindPrint Envoice LED issue - Any technician here?-img_5022.jpg  
Old 4th August 2020
  #20
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Labs's Avatar
 

Quote:
Originally Posted by Labs View Post

If you are only having problems on the meter on the left, you are probably drawing too much current through R5 due to a faulty BA682, so the burned resistor you replaced is a symptom, not the culprit.
Not much to add - but...

I have seen that brownish glue become conductive on some hi-fi gear that has come in for repairs. You could try just removing what is around the connectors (here, you can check with a meter for shorts to verify or discard the theory).

Gustav
Old 4th August 2020
  #21
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Rick Dalton's Avatar
Quote:
Originally Posted by _barnee View Post
The circuit on the back LED PCB.
Was all that flux there already or did you do that? ether way I'd get my meter a do continuity test from each joint, follow the trace to next joint, do them all and if you find any that are not infinity, that's not good, the flux could be causing a none connection. the thing to do after test, would be use a toothbrush some solvent and clean all those fluxed-up solder joints then reflow each one. If you have to, scrape a little beside each solder joint to expose the copper of the trace, and flow the solder over onto the clean copper of the trace.
Old 4th August 2020
  #22
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Labs's Avatar
 

Quote:
Originally Posted by Rick Dalton View Post
Was all that flux there already or did you do that? ether way I'd get my meter a do continuity test from each joint, follow the trace to next joint, do them all and if you find any that are not infinity, that's not good, the flux could be causing a none connection. the thing to do after test, would be use a toothbrush some solvent and clean all those fluxed-up solder joints then reflow each one.
Ah, yes - probably just be flux here.

but what he said.

Gustav
Old 4th August 2020
  #23
Hi guys,

Haven't done anything to the PCB.
The brown thing is pretty ugly actually. What could have done this?
Old 4th August 2020
  #24
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Rick Dalton's Avatar
Quote:
Originally Posted by _barnee View Post
Hi guys,

Haven't done anything to the PCB.
The brown thing is pretty ugly actually. What could have done this?
If you're talking about that goop looking stuff, that's flux, it is a acid that is found in some solder. With that being there, tells me that PCB has been worked on, and the look's of it, someone was trying to fix a problem by reflowing those solder joints or they replace that ribbon cable and those other components, which I find unlikely. As there's other way to check such, so it looks as though they were chasing and guessing at an issue.
Was this working when you got it.
Old 4th August 2020
  #25
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You can do a search on solder flux residue, but looking at this, someone was chasing probably the same issue youre having, youll notice on some of the switches, that they were not replaced or all the joints would look the same. Makes me wounder what the Main Board looks like. Also, it looks like they used plumbers flux, as some of it looks like this.
Old 4th August 2020
  #26
Quote:
Originally Posted by Rick Dalton View Post
If you're talking about that goop looking stuff, that's flux, it is a acid that is found in some solder. With that being there, tells me that PCB has been worked on, and the look's of it, someone was trying to fix a problem by reflowing those solder joints or they replace that ribbon cable and those other components, which I find unlikely. As there's other way to check such, so it looks as though they were chasing and guessing at an issue.
Was this working when you got it.
Yep, this was working when I got it.

It came from a music store. Took months for them to fix some of my units (not working "out of the box") and they gave me this MindPrint in the meantime so I could still have a preamp. I was then given the MindPrint as compensation.

Reading your comment, it looks the MindPrint has been badly operated. I didn't know about. I personally haven't worked the PCB in any other way than unsolder/solder the resistance in R5 a couple of weeks ago.
Old 4th August 2020
  #27
Quote:
Originally Posted by Rick Dalton View Post
You can do a search on solder flux residue, but looking at this, someone was chasing probably the same issue youre having, youll notice on some of the switches, that they were not replaced or all the joints would look the same. Makes me wounder what the Main Board looks like. Also, it looks like they used plumbers flux, as some of it looks like this.
Do I need to unsolder all faulty components, clean the board, re-solder the components with electronic flux?
Old 4th August 2020
  #28
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Rick Dalton's Avatar
Quote:
Originally Posted by _barnee View Post
Do I need to unsolder all faulty components, clean the board, re-solder the components with electronic flux?
That would probably be the thing to do, as you can see, they had to be chasing the same issue,,, wouldn't you say? Or why would they even be working in that problem area. Know what I mean? Main thing to look for, is the flux didn't eat or fracture any traces by the joints. You can scrape a little of that coating off if so, to expose good copper and just flow into the new exposed copper. You can use an magnifying app on a smart phone, to get a good look at all the joints, etc.
Old 5th August 2020
  #29
Quote:
Originally Posted by Rick Dalton View Post
That would probably be the thing to do, as you can see, they had to be chasing the same issue,,, wouldn't you say? Or why would they even be working in that problem area. Know what I mean?
To my surprise I am discovering they actually worked on it, and not nicely it seems.


Quote:
Originally Posted by Rick Dalton View Post
Main thing to look for, is the flux didn't eat or fracture any traces by the joints. You can scrape a little of that coating off if so, to expose good copper and just flow into the new exposed copper. You can use an magnifying app on a smart phone, to get a good look at all the joints, etc.
As a newbie this looks tough job to me, but I'll definitely have a look at it.
Thanks!
Old 5th August 2020
  #30
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Rick Dalton's Avatar
Quote:
Originally Posted by _barnee View Post
To my surprise I am discovering they actually worked on it, and not nicely it seems.




As a newbie this looks tough job to me, but I'll definitely have a look at it.
Thanks!
barnee, probably an easier way would be, get some acetone, some Q-tips, a toothbrush and clean all that, then hit all those joints with an soldering iron and a little solder. How hard is it going to be to take that main board out for a look?
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