Beginners Road To Repair Part 2 - Page 1
Forum section: electronics / beginners

author: don@cascadefellowship.org
author_rank: Contributor
timestamp: October 02, 2018, 07:38:22 pm
content: 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.

author: don@cascadefellowship.org
author_rank: Contributor
timestamp: October 02, 2018, 07:39:09 pm
content: Additional Pics

author: don@cascadefellowship.org
author_rank: Contributor
timestamp: October 02, 2018, 07:40:28 pm
content: Additional Pics

author: don@cascadefellowship.org
author_rank: Contributor
timestamp: October 02, 2018, 07:41:39 pm
content: Additional Pics

author: don@cascadefellowship.org
author_rank: Contributor
timestamp: October 02, 2018, 07:43:57 pm
content: 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!

author: tpowell1830
author_rank: Frequent Contributor
timestamp: October 02, 2018, 08:35:15 pm
content: Hi Don, the big electrolytics on the lower right in the first pic seem to have bulges on the top, can you verify?

author: Wimberleytech
author_rank: Super Contributor
timestamp: October 02, 2018, 09:12:19 pm
content: 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.

author: iainwhite
author_rank: Unknown
timestamp: October 03, 2018, 02:25:46 am
content: For "Good" solder wick, I would suggest:Chemtronics Soder-Wick SW 80 series - e.g. part number 80-3-5orMG Chemicals 400 series Super Wick - e.g. part number 443If you do a lot of desoldering and want to spend more:Hakko FR-301 handheld vacuum desolder tool

author: BradC
author_rank: Super Contributor
timestamp: October 03, 2018, 02:36:42 am
content: Quote from: don@cascadefellowship.org on October 02, 2018, 07:43:57 pmHave you got an operation manual? What does a blinking power led mean?

author: alsetalokin4017
author_rank: Super Contributor
timestamp: October 03, 2018, 03:01:18 am
content: 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?

author: onesixright
author_rank: Frequent Contributor
timestamp: October 03, 2018, 06:59:41 am
content: Hi!Sent from my iPad using Tapatalk

author: Shock
author_rank: Super Contributor
timestamp: October 03, 2018, 01:07:41 pm
content: 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.

author: Shock
author_rank: Super Contributor
timestamp: October 03, 2018, 01:43:46 pm
content: 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.

author: don@cascadefellowship.org
author_rank: Contributor
timestamp: October 03, 2018, 04:42:39 pm
content: Quote from: tpowell1830 on October 02, 2018, 08:35:15 pmSure. 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.

author: don@cascadefellowship.org
author_rank: Contributor
timestamp: October 03, 2018, 04:48:30 pm
content: Quote from: Wimberleytech on October 02, 2018, 09:12:19 pmYou bet.IC 6-8 LM324NIC 1 & 3 TL074CNIC 4 LM13700NIC 2 TL072CN

author: don@cascadefellowship.org
author_rank: Contributor
timestamp: October 03, 2018, 04:50:46 pm
content: Quote from: BradC on October 03, 2018, 02:36:42 amYes I do have the manual and a data sheet. Sadly, the troubleshooting section is pretty thin.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: October 03, 2018, 04:51:16 pm
content: Quote from: don@cascadefellowship.org on October 03, 2018, 04:42:39 pmFrom 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.

author: don@cascadefellowship.org
author_rank: Contributor
timestamp: October 03, 2018, 05:02:13 pm
content: Quote from: alsetalokin4017 on October 03, 2018, 03:01:18 amI 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...

author: don@cascadefellowship.org
author_rank: Contributor
timestamp: October 03, 2018, 05:02:55 pm
content: Quote from: alsetalokin4017 on October 03, 2018, 03:01:18 amAdditional pics.

author: don@cascadefellowship.org
author_rank: Contributor
timestamp: October 03, 2018, 05:03:26 pm
content: Quote from: onesixright on October 03, 2018, 06:59:41 amHello!

author: don@cascadefellowship.org
author_rank: Contributor
timestamp: October 03, 2018, 05:09:08 pm
content: Quote from: Shock on October 03, 2018, 01:07:41 pmWow 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.

author: don@cascadefellowship.org
author_rank: Contributor
timestamp: October 03, 2018, 05:10:50 pm
content: Quote from: Shock on October 03, 2018, 01:07:41 pmI have a signal generator that I can use for input and I don't know how to move this thread, yet.

author: don@cascadefellowship.org
author_rank: Contributor
timestamp: October 03, 2018, 05:26:49 pm
content: Quote from: Shock on October 03, 2018, 01:43:46 pmI 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.

author: don@cascadefellowship.org
author_rank: Contributor
timestamp: October 03, 2018, 05:28:51 pm
content: Quote from: tpowell1830 on October 03, 2018, 04:51:16 pmI overlooked the error in the manual as it was under installation and not troubleshooting. Here's what it says:4. OPERATION & SYSTEM SET-UP4.1 Start-up ProcedureAn 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.

author: don@cascadefellowship.org
author_rank: Contributor
timestamp: October 03, 2018, 07:01:44 pm
content: Testing IC 1 in circuit. TL074NNo 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?

author: don@cascadefellowship.org
author_rank: Contributor
timestamp: October 03, 2018, 10:21:37 pm
content: Testing IC 2 in circuit. TL072CNPin 3 connected to ground. No pins shorted together.Pin 1 Out 1 .748 volts (steady)Pin 2 In 1- .088 volts (steady)Pin 3 In 1+ .002 volts (steady)Pin 4 Vcc- .753 volts (steady)Pin 5 In 2+ .745 volts (steady)Pin 6 In 2- .207 volts (steady)Pin 7 Out 2 .641-.646 volts (fluctuates)Pin 8 Vcc+ 15 volts (steady)

author: tpowell1830
author_rank: Frequent Contributor
timestamp: October 03, 2018, 11:09:32 pm
content: Quote from: don@cascadefellowship.org on October 03, 2018, 10:21:37 pmI am unfamiliar with this setup and have not done much troubleshooting on such a complex board, just to qualify what I am saying.To be perfectly honest with you, as some of the more accomplished board troubleshooters will tell you, these numbers mean very little unless you describe the setup that you are using for your test, such as what meter you are using, what is the settings that you are using, what is the input signal? Are these opamps there to accept the audio input? Do you have the schematic to show where and how these are used? Are you measuring AC or DC? Are you injecting a test signal on the input?I am sure there will be 40 more questions from more learned people.

author: don@cascadefellowship.org
author_rank: Contributor
timestamp: October 03, 2018, 11:21:15 pm
content: Quote from: tpowell1830 on October 03, 2018, 11:09:32 pmYes, of course. You make excellent points! I'm using my multi-meter (Fluke 117) to measure voltages at each pin with the red lead while the black lead is on ground. I'm measuring DC voltages. The unit is powered on with no input signal. The Gain and Drive controls are all the way down. I'm using this as an opportunity to learn what each pin represents on the op amp and I'm documenting the voltages to see if there are any obvious signs of a malfunction. I should preface that by saying, I'm learning these things myself and would likely not recognize an obvious malfunction if it fell out the sky, landed on my face and started to wiggle.I have not net been able to find a schematic so I'm open to learning how to draw one up from scratch while doing this repair.That said, I'm open to any and all advice. The more newbie oriented the better. I have no formal training in electronics repair but I'm getting better at learning to identify components and research online.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: October 03, 2018, 11:30:32 pm
content: Quote from: don@cascadefellowship.org on October 03, 2018, 11:21:15 pmLOL, that should be a classic, nearly fell out my seat on that one...

author: don@cascadefellowship.org
author_rank: Contributor
timestamp: October 04, 2018, 12:37:10 am
content: Quote from: tpowell1830 on October 03, 2018, 11:30:32 pmAll credit to Dan Aykroyd.

author: Shock
author_rank: Super Contributor
timestamp: October 04, 2018, 01:01:23 am
content: I can see Q19 which is a 7815C (+15V) and a TIP31C, TIP32C. What is Q22?

author: don@cascadefellowship.org
author_rank: Contributor
timestamp: October 04, 2018, 01:45:19 am
content: Quote from: Shock on October 04, 2018, 01:01:23 amThat's an L7915CV.The output measures .755 volts to ground (steady). And the input measures -2.365-2.372 volts to ground (fluctuates).

author: Shock
author_rank: Super Contributor
timestamp: October 04, 2018, 03:40:21 am
content: Quote from: don@cascadefellowship.org on October 04, 2018, 01:45:19 amWell that may explain where the -15V went. What could cause a low input voltage? What do you think is the next step?I already know the answers but it helps if you think it through.

author: don@cascadefellowship.org
author_rank: Contributor
timestamp: October 09, 2018, 03:29:47 pm
content: Quote from: Shock on October 04, 2018, 03:40:21 amBased on my limited experience and my last repair, a short along the signal path before the input could cause a low input voltage.Q19 Voltage Regulator L7815CVInput 26.98-27.47 volts to ground (fluctuates, ramps up slowly)Output 15.00 volts to ground (steady)Ground 0Q20 Transistor TIP31CBase 28.23 volts (steady)Collector 46.32-46.43 volts (fluctuates)Emitter 27.62-27.64 volts (fluctuates)Q21 Transistor TIP32CBase -2.92-2.97 volts (fluctuates)Collector -46.39-46.48 volts (fluctuates)Emitter -2.43-2.49 volts (fluctuates)Q22 Voltage Regulator L7915CVInput -2.365-2.372 volts to ground (fluctuates)Output .755 volts to ground (steady)Ground 0

author: Shock
author_rank: Super Contributor
timestamp: October 09, 2018, 07:15:04 pm
content: Ok sounds like you might be stuck for ideas.You're close. A short on the regulators output also may cause the voltage to drop or an over current situation may cause the regulator to fail or be damaged.So remove the -15V regulator and then see if the input voltage comes back up by measuring input to ground. Not all components are safe to just remove (there are exceptions) but this is a power rail and we can see shes pretty much dead anyway.With the power removed and circuit discharged measure resistance (ohms) across the output pin to ground and if you got no input voltage measurement before in that previous check measure the input to ground as well. Check you have a low resistance path to other grounds. I can see on the PCB that the grounds appear common between the +15V and -15V their pinouts are not the same. Look at datasheets!Note: to confirm if a circuit is discharged we can measure voltage across capacitors or the voltage across the place you want to take your measurement. Some devices like CRTs microwaves and large power supplies can hold charge for quite some time. Another way to make it easier to discharge circuits sometimes is to flip the power off while the device is on and then wait a little and unplug it. If you don't test for voltage before you check with ohms or diode test with certain meters you will damage them. You will wonder why you are getting bad measurements and it's another good reminder that if there is voltage present you need to then double check the device is off unplugged and isolated from the mains.When I measure to see if a circuit is shorted I normally take positive to negative, negative to positive and then I do the same with a diode test. So you get resistance but also can "characterize" the circuit for a potential short and see if there is a charging capacitor on that circuit or a semiconductor or some other voltage drop. If you did this with the regulator still in circuit it could be misleading if two faults are present i.e. short on output causes the regulator to fail.If you have a power supply that is high enough to supply the -15V input of the removed regulator (you go look up the datasheet) you can test it out of circuit. It may need a heatsink and/or get hot quick. If it produces an output voltage of -15V it may be inconclusive test still without a load (it's faulty only under load), but if gives you an idea and you can also measure it for a short.If you have a regulated power supply that has a floating output and adjustable current limiting you can also power the amp directly from the supply by connecting it to ground and the output pin of where the -15V regulator was. By current limiting you can monitor the voltage across the op amp (where -15V should have been present) and slowly bring up the current. You would expect to see the voltage rise. If it doesn't you have a high current path to ground somewhere.In case it's not obvious, if your bench test power supply is floating (no reference to ground/earth or to the circuit under test) by reversing the positive and negative over it becomes a "negative supply".There are a lot of concepts covered here.