Author Topic: Beginners Road To Repair Part 2  (Read 5749 times)

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Offline don@cascadefellowship.orgTopic starter

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Beginners Road To Repair Part 2
« on: October 02, 2018, 07:38:22 pm »
Hi all!  So I have my second repair project ready to go.  If you recall, my first repair was an active DI box that was a success due to the help I found on this forum! Here is a brief summary of what I learned from the last project (https://www.eevblog.com/forum/beginners/beginners-road-to-repair/):

I'm going to note some things here for future reference so I can build on what I learned.

My Steps For Repair:

1. Test external power supplies.

2. Visually inspect components on PCB's looking for things that are blown or burned.

3. Check input and output of voltage regulators.

4. If there's a problem on a voltage rail then check each component on that rail until you find the problem.

Things I Learned:

-Desoldering braid is really annoying.  I need a faster desoldering solution.
-Electrolytic capacitors tend to go bad so check those first.

This current repair project is an Ampetronic ILD9 Induction Loop Driver that is used to broadcast audio to persons with listening assistance devices.  On power up, the Compression LED’s under the Gain control goes right into overload and the Power LED blinks continuously.  When operating normally, the Compression LED’s will follow the signal level passing through the unit and the Power LED will lit and not blinking.

I’ve checked the fuse (and spare) and both are functional.  I’ve made a visual inspection and found no obvious signs of damage.  There’s no burnt smell either.  I’m going to continue by checking the voltage regulators located near the bipolar junction transistors. 

If anyone would like to offer any suggestions, tips, advice or just say hi, I welcome your comments.  Thank you!  I hope I can get this running again.
 

Offline don@cascadefellowship.orgTopic starter

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Re: Beginners Road To Repair Part 2
« Reply #1 on: October 02, 2018, 07:39:09 pm »
Additional Pics
 

Offline don@cascadefellowship.orgTopic starter

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Re: Beginners Road To Repair Part 2
« Reply #2 on: October 02, 2018, 07:40:28 pm »
Additional Pics
 

Offline don@cascadefellowship.orgTopic starter

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Re: Beginners Road To Repair Part 2
« Reply #3 on: October 02, 2018, 07:41:39 pm »
Additional Pics
 

Offline don@cascadefellowship.orgTopic starter

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Re: Beginners Road To Repair Part 2
« Reply #4 on: October 02, 2018, 07:43:57 pm »
I've been in contact with the manufacturer and I'm going to try and get a schematic for the unit.  I have not found one online yet.  Maybe this will be an opportunity to create my first schematic!
 

Offline tpowell1830

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Re: Beginners Road To Repair Part 2
« Reply #5 on: October 02, 2018, 08:35:15 pm »
Hi Don, the big electrolytics on the lower right in the first pic seem to have bulges on the top, can you verify?
PEACE===>T
 

Offline Wimberleytech

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Re: Beginners Road To Repair Part 2
« Reply #6 on: October 02, 2018, 09:12:19 pm »
I use solder braid but if you buy the cheap stuff...it is crap.

You will know if there is an issue with the caps once you measure the supply voltages.  This appears to be a linear supply, so a leaky or high ESR cap is unlikely to be the killer.

Can you provide the IC part numbers? Cannot read them from the pictures.
 

Offline iainwhite

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Re: Beginners Road To Repair Part 2
« Reply #7 on: October 03, 2018, 02:25:46 am »
For "Good" solder wick, I would suggest:

Chemtronics Soder-Wick SW 80 series - e.g. part number 80-3-5
or
MG Chemicals 400 series Super Wick   - e.g. part number 443

If you do a lot of desoldering and want to spend more:
Hakko FR-301 handheld vacuum desolder tool
 
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Offline BradC

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Re: Beginners Road To Repair Part 2
« Reply #8 on: October 03, 2018, 02:36:42 am »
I've been in contact with the manufacturer and I'm going to try and get a schematic for the unit.  I have not found one online yet.  Maybe this will be an opportunity to create my first schematic!

Have you got an operation manual? What does a blinking power led mean?
 

Offline alsetalokin4017

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Re: Beginners Road To Repair Part 2
« Reply #9 on: October 03, 2018, 03:01:18 am »
Is it intended to be operated without a load at the output loop connection?

Also, it might be nice to have a photo or two of the underside of the PCB.


And I'm wondering if there is a microprocessor and memory in there. Could the problem be firmware corruption or error?
« Last Edit: October 03, 2018, 03:03:32 am by alsetalokin4017 »
The easiest person to fool is yourself. -- Richard Feynman
 

Offline onesixright

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Re: Beginners Road To Repair Part 2
« Reply #10 on: October 03, 2018, 06:59:41 am »
Hi!


Sent from my iPad using Tapatalk
 

Offline Shock

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Re: Beginners Road To Repair Part 2
« Reply #11 on: October 03, 2018, 01:07:41 pm »
I recommend you move this post to the repair section of the forums.

Obviously be careful with a live circuit could be any voltages present. In the manual it states that the constant flashing is a amplification self test failure. It puts the unit in some kind of safe mode. I would test the op amps and transistors. Won't hurt to check the different power rails though especially if there is +/- for opamps and the logic supply.

There is a gain control pot as well you might want to measure where it was set at and then lower it so see if it makes any difference as well as apply an input signal. If you need a cheap floating audio signal source you can buy cheap Chinese function generators on ebay starting at about $10-$20.
Soldering/Rework: Pace ADS200, Pace MBT350
Multimeters: Fluke 189, 87V, 117, 112   >>> WANTED STUFF <<<
Oszilloskopen: Lecroy 9314, Phillips PM3065, Tektronix 2215a, 314
 

Offline Shock

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Re: Beginners Road To Repair Part 2
« Reply #12 on: October 03, 2018, 01:43:46 pm »
When I see big wattage resistors the first thing I look for is dry solder joints and I can see there is a possible dry joint there. If in doubt give them a reflow and ensure you have a low ohm path on any trace that connects to them.

The transistors and regulators on the heatsink can have insulated screws so make sure you keep track of what one was used where. That is a good early lesson to learn that because something is on  a heatsink doesn't mean it's meant to be electrically bonded to it. Heatsinks on many devices are a touch hazard and aren't always safety labelled.

That heatsink looks like it might be attached to the chassis. You can test this though to be sure and if other parts of the circuit that look like they should be are in fact properly connected.

The two electrolytic filter caps have plastic disc covers that often warp as the plastic shrinks a little. Nothing too concerning if the feel flat when you push them down.
Soldering/Rework: Pace ADS200, Pace MBT350
Multimeters: Fluke 189, 87V, 117, 112   >>> WANTED STUFF <<<
Oszilloskopen: Lecroy 9314, Phillips PM3065, Tektronix 2215a, 314
 

Offline don@cascadefellowship.orgTopic starter

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Re: Beginners Road To Repair Part 2
« Reply #13 on: October 03, 2018, 04:42:39 pm »
Hi Don, the big electrolytics on the lower right in the first pic seem to have bulges on the top, can you verify?

Sure.  It's possible that the one furthest to the right might have a minute bulge.  Very, very small though.  Here's a pic with the straight edge of the frame as a reference.
 

Offline don@cascadefellowship.orgTopic starter

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Re: Beginners Road To Repair Part 2
« Reply #14 on: October 03, 2018, 04:48:30 pm »
I use solder braid but if you buy the cheap stuff...it is crap.

You will know if there is an issue with the caps once you measure the supply voltages.  This appears to be a linear supply, so a leaky or high ESR cap is unlikely to be the killer.

Can you provide the IC part numbers? Cannot read them from the pictures.

You bet. 

IC 6-8 LM324N

IC 1 & 3 TL074CN

IC 4 LM13700N

IC 2 TL072CN
« Last Edit: October 03, 2018, 10:04:55 pm by don@cascadefellowship.org »
 

Offline don@cascadefellowship.orgTopic starter

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Re: Beginners Road To Repair Part 2
« Reply #15 on: October 03, 2018, 04:50:46 pm »
I've been in contact with the manufacturer and I'm going to try and get a schematic for the unit.  I have not found one online yet.  Maybe this will be an opportunity to create my first schematic!

Have you got an operation manual? What does a blinking power led mean?

Yes I do have the manual and a data sheet.  Sadly, the troubleshooting section is pretty thin. 

 

Offline tpowell1830

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Re: Beginners Road To Repair Part 2
« Reply #16 on: October 03, 2018, 04:51:16 pm »
Hi Don, the big electrolytics on the lower right in the first pic seem to have bulges on the top, can you verify?

Sure.  It's possible that the one furthest to the right might have a minute bulge.  Very, very small though.  Here's a pic with the straight edge of the frame as a reference.

From that angle, doesn't seem to be bulging at all. If they were bulging, wouldn't mean that is your problem, only time to change them out with your maintenance. There have been thoughts that the firmware is telling you something with the blinking LED, do you have error codes or manual?

EDIT: I see you already posted that you don't have good information.
« Last Edit: October 03, 2018, 04:55:27 pm by tpowell1830 »
PEACE===>T
 

Offline don@cascadefellowship.orgTopic starter

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Re: Beginners Road To Repair Part 2
« Reply #17 on: October 03, 2018, 05:02:13 pm »
Is it intended to be operated without a load at the output loop connection?

Also, it might be nice to have a photo or two of the underside of the PCB.


And I'm wondering if there is a microprocessor and memory in there. Could the problem be firmware corruption or error?

I think it can be operated without a load.  Certainly let me know if I'm wrong.  It's basically a radio.  It drives signal through a copper wire in the floor which can be received by hearing aids and other such devices.

I don't believe this unit has any type of software, firmware, drivers, etc...
 

Offline don@cascadefellowship.orgTopic starter

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Re: Beginners Road To Repair Part 2
« Reply #18 on: October 03, 2018, 05:02:55 pm »
Is it intended to be operated without a load at the output loop connection?

Also, it might be nice to have a photo or two of the underside of the PCB.


And I'm wondering if there is a microprocessor and memory in there. Could the problem be firmware corruption or error?

Additional pics.
 

Offline don@cascadefellowship.orgTopic starter

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Re: Beginners Road To Repair Part 2
« Reply #19 on: October 03, 2018, 05:03:26 pm »
Hi!


Sent from my iPad using Tapatalk

Hello!
 

Offline don@cascadefellowship.orgTopic starter

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Re: Beginners Road To Repair Part 2
« Reply #20 on: October 03, 2018, 05:09:08 pm »
I recommend you move this post to the repair section of the forums.

Obviously be careful with a live circuit could be any voltages present. In the manual it states that the constant flashing is a amplification self test failure. It puts the unit in some kind of safe mode. I would test the op amps and transistors. Won't hurt to check the different power rails though especially if there is +/- for opamps and the logic supply.

There is a gain control pot as well you might want to measure where it was set at and then lower it so see if it makes any difference as well as apply an input signal. If you need a cheap floating audio signal source you can buy cheap Chinese function generators on ebay starting at about $10-$20.

Wow I completely missed that!  Section 4.1.  Thanks!!! 

I did adjust the gain and drive pots to see if there was any change, which there was not.  Power LED continues to blink and the Compression LED's are in Overload.

Instead of checking the voltage regulators first I think I'll start with op amps and transistors.  Or perhaps just getting into the habit of checking voltage regulators first and them op amps and transistors would be better?  Just looking for a general order of basic component checks, that sort of thing.
 

Offline don@cascadefellowship.orgTopic starter

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Re: Beginners Road To Repair Part 2
« Reply #21 on: October 03, 2018, 05:10:50 pm »
I recommend you move this post to the repair section of the forums.

Obviously be careful with a live circuit could be any voltages present. In the manual it states that the constant flashing is a amplification self test failure. It puts the unit in some kind of safe mode. I would test the op amps and transistors. Won't hurt to check the different power rails though especially if there is +/- for opamps and the logic supply.

There is a gain control pot as well you might want to measure where it was set at and then lower it so see if it makes any difference as well as apply an input signal. If you need a cheap floating audio signal source you can buy cheap Chinese function generators on ebay starting at about $10-$20.

I have a signal generator that I can use for input and I don't know how to move this thread, yet.
 

Offline don@cascadefellowship.orgTopic starter

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Re: Beginners Road To Repair Part 2
« Reply #22 on: October 03, 2018, 05:26:49 pm »
When I see big wattage resistors the first thing I look for is dry solder joints and I can see there is a possible dry joint there. If in doubt give them a reflow and ensure you have a low ohm path on any trace that connects to them.

The transistors and regulators on the heatsink can have insulated screws so make sure you keep track of what one was used where. That is a good early lesson to learn that because something is on  a heatsink doesn't mean it's meant to be electrically bonded to it. Heatsinks on many devices are a touch hazard and aren't always safety labelled.

That heatsink looks like it might be attached to the chassis. You can test this though to be sure and if other parts of the circuit that look like they should be are in fact properly connected.

The two electrolytic filter caps have plastic disc covers that often warp as the plastic shrinks a little. Nothing too concerning if the feel flat when you push them down.

I can see that identifying a dry solder joint is going to take some practice.  It's as if there's a small circle around the dry joint and nothing but a smooth slope of solder on a healthy joint.

 

Offline don@cascadefellowship.orgTopic starter

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Re: Beginners Road To Repair Part 2
« Reply #23 on: October 03, 2018, 05:28:51 pm »
Hi Don, the big electrolytics on the lower right in the first pic seem to have bulges on the top, can you verify?

Sure.  It's possible that the one furthest to the right might have a minute bulge.  Very, very small though.  Here's a pic with the straight edge of the frame as a reference.

From that angle, doesn't seem to be bulging at all. If they were bulging, wouldn't mean that is your problem, only time to change them out with your maintenance. There have been thoughts that the firmware is telling you something with the blinking LED, do you have error codes or manual?

EDIT: I see you already posted that you don't have good information.

I overlooked the error in the manual as it was under installation and not troubleshooting.  Here's what it says:

4. OPERATION & SYSTEM SET-UP
4.1 Start-up Procedure
An internal self test system has been incorporated in the equipment. When switching on, the power LED will flash for some 5 seconds, during which time the amplifier is tested for correct operation. If correct, the unit will then switch to an operational mode, and the LED will remain on without flashing. However, if an amplifier or loop fault exists, or develops during operation, the equipment will return to a safe mode, and the LED will flash continuously.
 

Offline don@cascadefellowship.orgTopic starter

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Re: Beginners Road To Repair Part 2
« Reply #24 on: October 03, 2018, 07:01:44 pm »
Testing IC 1 in circuit.  TL074N

No pins connected to ground.  Pins 6 and 7 are shorted together (continuity test then visually confirmed by looking at the trace)

Pin 1   Out 1   4.053-4.058 volts (fluctuates)

Pin 2   In 1-   3.072-3.078 volts (fluctuates)

Pin 3   In 1+   1.507 volts (steady)

Pin 4   Vcc     15.00 volts (steady)

Pin 5   In 2+   1.513-1.517 (fluctuates)

Pin 6   In 2-   2.536-2.539 volts (fluctuates)

Pin 7   Out 2   2.527-2.529 volts (fluctuates)

Pin 8   Out 3   2.087 volts (steady)

Pin 9   In 3-   2.077 volts (steady)

Pin 10  In 3+   1.651 volts (steady)

Pin 11  Vee     .738 volts (steady)

Pin 12  In 4+   1.644 volts (steady)

Pin 13  In 4-   2.076 volts (steady)

Pin 14  Out 4   2.084 volts (steady)

Some questions:

Shouldn't the + and - pins of each input read the same voltage?  Is it correct to assume they should be equal?  I'm an audio guy so I guess I may be assuming that a positive voltage should have an equal and opposite negative voltage for a single input.

How steady should the readings be when testing op amps or other electrical components?  I guess in theory I would be comfortable in saying the more steady the better but are fluctuations in the order of thousandths of a volt a problem or to be expected?
 


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