Testing receivers. - Page 1
Forum section: electronics / beginners

author: Earl
author_rank: Contributor
timestamp: December 21, 2015, 03:41:13 am
content: Hi all, newbie here, I have just found supply of used home theater receivers,various brands.Some will be working,and some not working.My question is, how can I test them to see if they are working, without taking back off, or sending them to repairman ?Thanks for any helpfull tips.

author: Earl
author_rank: Contributor
timestamp: December 21, 2015, 03:43:57 am
content: PS, I will be buying these for resale.

author: Richard Crowley
author_rank: Super Contributor
timestamp: December 21, 2015, 04:34:05 am
content: Are you talking about testing individual units before purchasing them?Or are you talking about testing units you already have to identify the functional vs. dead ones?I would think about setting up a "test jig" where you have power, input signals (antenna, cable, satellite, whatever) and output to a standard screen (or two, one for SD and one for HD?) Then you can just quickly connect all the inputs and outputs, turn it on and see if the magic smoke comes out, or if it actually works.

author: Brumby
author_rank: Unknown
timestamp: December 21, 2015, 07:29:03 am
content: In testing whether something works - especially for resale - you will need to go through a reasonably thorough process, checking all inputs, outputs and functions. Step 1 would be this:Quote from: Richard Crowley on December 21, 2015, 04:34:05 amStep 2 would be to set up a testing 'script' - a list of all the things you want to test and step through this list for each unit.If you wanted to, you could run a spreadsheet where you record all the results - including the faults found. When the testing is finished, you would then have a list of equipment for immediate resale (with documented testing results) and others for potential repair or sold for parts.

author: jeroen79
author_rank: Frequent Contributor
timestamp: December 21, 2015, 09:20:43 am
content: Taking the back off wouldn't be necessary for an initial test. You can just test the inputs and outputs.But a look under the hood does't hurt either.For audio you could record some test tones or a 20Hz to 20kHz sweep.For video you could have a dvd player ready. Maybe you could make a test movie and burn it to DVD.For the testing script I would start with this:-Take unit from the stack.-Write down brand, type, serial number.-(optional)Search online for relevant documentation.-Examine for and note external defects.-(optional)Look for internal defects.-(optional)Remove any dust while the cover is off-Write down available inputs and outputs.-Now work through the inputs and outputs and note how well they work.If you want to be really thorough you could test each input with each output.-While working the controls on the front note howwell they feel.-Is the display in good order?-Finally give an overall verdict on the unit's state.You could be less thorough with the paperwork but the more you write down now the less chance you have of having to retest something later.

author: Earl
author_rank: Contributor
timestamp: December 21, 2015, 03:18:16 pm
content: Thanks Richard, Brumby and jeroen,I will be buying bulk,and then initially testing for live and dead ones, can I do that with multi meter?FYI.I am just venturing in to electronics, from buying and selling a variety of other goods on ebay , where I am a power seller.I am at an age where I need to slow down a little, and I have always wanted to learn how to repair home used electronics.I have done a bit of research online, and am sure I can test for continuity,voltage, and test resistors,fuses etc; with the right tools.I just need some advice/ help from knowledgable guys like yourselves and others in this forum.I really appreciate you guys taking the time to answer newbie postings, thank you

author: Brumby
author_rank: Unknown
timestamp: December 21, 2015, 03:39:04 pm
content: There's a limit to what you can test with a multimeter.In short, without taking the cover off and poking around, you'll only be able to test continuity through the mains lead. Even then, a transformer is the only load you will get any sort of clear reading. If there's a switchmode power supply inside, then you aren't going to get much useful information from a multimeter.Plug it in and turn it on is the first step.Watch out for the Magic Smoke escaping, listen for pyrotechnic sound effects and keep on the lookout for that 'stressed electrical' smell.If all good, then go through the stuff already mentioned.Your multimeter isn't going to get a lot of mileage until you start opening up the faulty gear and start troubleshooting.

author: Earl
author_rank: Contributor
timestamp: December 21, 2015, 04:12:35 pm
content: Thanks brumby, good info.What tools would you suggest for me to have,just starting out?.PS, Where in Australia are you?

author: Brumby
author_rank: Unknown
timestamp: December 21, 2015, 05:09:36 pm
content: - A decent multimeter (don't ask me for any recommendations, I'm well outclassed by other members here on that knowledge front). Having a second one is sometimes very useful.- Pliers (needle nose and bull nose)- Good side cutters (flush cutting)- Screwdrivers - flat and phillips of varying sizes- Other screwdriver bits for torx, allen keys, etc. - There's a wide range of potential fasteners youcouldcome across, but you'll find out about these as you encounter more equipment with 'creative' solutions- Soldering station (temperature controlled) - and desoldering gear. You don't have to pay a fortune for something decent, but don't skimp. The soldering iron is your main tool, so you don't want a liability in your hand.- FINE solder ~ 0.5 mm; 63/37 for preference but 60/40 will do. With fine solder, it is easier to control the amount fed into a joint. Too much solder can be as bad as too little.- Flux (there are a couple of options here)- Maybe not necessary when first starting out, but if your budget allows for it - and you find you need to know more of what's going on inside something - an oscilloscope. They're not the cheapest bit of kit, but properly driven, can yield extremely useful information.- A well lit work area with suitable bench space (It has been proven and unanimously endorsed that there is no such thing as too much bench space.)- A bench power supply - maybe. They can be handy if you need to power something independently. I'd suggest starting out with something like 30V 3A with current limiting and short circuit protection. They're easy enough to find and not too expensive and even if you find you need something more elaborate, it can still be useful as a second supply.- I'd also recommend a hot air/rework station. These are good for safe heating of heatshrink through to SMD reflow as well as being a controllable source of heat if you think you have a heat sensitive fault. They can also pre-heat a large metal plate that sucks the heat out of your soldering iron when trying to solder to it.Other equipment like function generators and so on are a bit more specialised and you will know what you need when you need to do something that can't be done with what you've got.If you're going to be working with receivers, you'll need sources - such as TV signals, DVD/Blu-ray player, etc. as well as output devices like monitors, speakers and so on.Along the way, you are also going to need a variety of patch cables. I won't even try to start a list of these. Just start off with a couple and if you leave them in a quiet corner, theywillmultiply. You'll probably end up with an array of regular cables and a few custom jobs. If you are organised, then you can give them homes, but if not - get a fruit box. Maybe two.Well, that's where I'd start - but I keep thinking I've missed something....................

author: Earl
author_rank: Contributor
timestamp: December 21, 2015, 07:21:50 pm
content: Thanks brumby, I have all the tools down to and including soldering iron.You lost me on power supply and hot air items.Do they have specific names?

author: Richard Crowley
author_rank: Super Contributor
timestamp: December 21, 2015, 08:03:30 pm
content: Quote from: Earl on December 21, 2015, 07:21:50 pmDave has done several reviews of "bench power supply" units.Alas, there is no running "box score" of what gear (oscilloscopes, meters, power supplies, signal generators, etc.) were reviewed good vs. bad.If you are triaging repair of consumer gear, a bench supply may not be as high on your priority list.I recently purchased this to work with SMD boards...http://www.amazon.com/gp/product/B00I01H1GMIt seems to work reasonably well. But it is my first hot-air equipment, so I have no basis for comparison.

author: Earl
author_rank: Contributor
timestamp: December 21, 2015, 10:02:12 pm
content: Looks like a nice unit Richard.I see no more available on amazon,.I assume the hot air is to heat the board, so you don't damage sensitive parts, is that right?

author: Richard Crowley
author_rank: Super Contributor
timestamp: December 21, 2015, 11:43:52 pm
content: The hot air is to melt the solder that holds the SMD components to the board (so you can remove defective components).You will probably not initially be repairing units down to the component-level, and SMD even more (or less) so.@Brumby is also suggesting it could be useful for "thermal diddling" certain components to see if they might be causing thermal-related symptoms. We also use a spray-can of coolant (used to be Freon) to quickly cool/freeze components for the same thermal trouble-shooting reasons.There are other very similar hot-air/soldering iron units on Amazon. My choice of that one was from a collection of 3-4 that were almost identical.

author: Brumby
author_rank: Unknown
timestamp: December 22, 2015, 03:05:25 am
content: The biggest use of my hot air gun has been for heatshrink. You dial up the right temperature for the heatshrink and get a decent flow of air which results in quick shrinking and minimal risk of overheating anything in the vicinity. The first time I tried it, I couldn't stop smiling. It was so quick and easy and non-threatening to surrounding components. I'd recommend one for that alone.It's also good to have for SMD work - if you ever get involved with that.

author: Brumby
author_rank: Unknown
timestamp: December 22, 2015, 03:12:17 am
content: Don't worry about a benchtop power supply at the moment. Working on already built equipment means you shouldn't need one as everything inside will already have arrangements for power.The time to get one is when you work out you need one - same as an oscilloscope and other test gear.

author: Earl
author_rank: Contributor
timestamp: December 22, 2015, 03:48:27 am
content: I will have to remove components, if they are defective.I thought I could remove components using soldering iron, to melt solder from the back of the board, am I wrong?

author: Brumby
author_rank: Unknown
timestamp: December 22, 2015, 04:40:15 am
content: No, you are not wrong - but there can be challenging situations.With two lead axial components, it is simple enough - just heat one lead and pull it out, then heat the other and the component is free. The solder doesn't cause any problems (usually).With RB capacitors (where both leads come out the same end) sitting hard against the PCB, this can get a little tricky. When you get to multi pin devices, it really gets difficult to remove components quickly and avoid damaging the tracks and pads. There are special tips you can get for your soldering iron (to desolder a 16 pin DIP IC for example) and there is the broad brush method with a hot air gun (not advised unless you are speed stripping boards for second hand components - a real industry in some parts of Asia.)This is where removing the solder helps. There are 3 basic ways of doing this:1. Vacuum solder sucker. There are various types, but essentially operate the same way. A spring loaded plunger is 'armed', you heat up the solder, apply the tip to the joint and release the plunger.2. Desoldering braid (or wick). Works just as in the picture. Good flux coverage is important.3. Desoldering station. This is like a soldering iron, but with a hole through the middle of the tip and a vacuum pump connected through it. (I just got one myself - which is this one. Dave did a video on it.)Situations can vary and one technique may not work, so it's good to have more than one available. I strongly suggest desoldering braid/wick is one of them. (Get good quality - don't get the cheap stuff, as it will cost you more in the long run in both time and overheating of components trying to get it to work.)Even with the best of these tools and top notch technique, not all desoldering efforts will result in a component just falling out. Sometimes leads are bent over, but often there will be a tiny point of contact with a miniscule bit of solder still hanging in there. These are often broken by pushing sideways on the lead when you will often hear a satisfying little click as the bond breaks - but don't do this if you can still see some solder around the lead. Murphy will guarantee it will be strong enough to hang a bowling ball from it.

author: Earl
author_rank: Contributor
timestamp: December 22, 2015, 06:40:11 pm
content: Thanks Richard, good info, I will Google about coolant use, so I don't have ask you guys heaps of questions.

author: Earl
author_rank: Contributor
timestamp: December 22, 2015, 06:54:46 pm
content: Thanks Brumby, with all the help and advice I am getting from you guys, and the online research I am doing, I am feeling more confident about my decision to venture into electronics.I am sure I will be asking you guys for help in the new yearMERRY CHRISTMAS AND HAPPY NEW YEAR, TO ALL YOU GUYS.

author: Richard Crowley
author_rank: Super Contributor
timestamp: December 22, 2015, 07:52:40 pm
content: This is the kind of freeze spray I was referring to...http://www.amazon.com/MG-Chemicals-Super-Spray-Aerosol/dp/B008UH3NB8It is useful for identifying problem components in situations where something works OK until it warms up.

author: Shock
author_rank: Super Contributor
timestamp: December 22, 2015, 09:32:28 pm
content: Something like an older broken receiver without speakers, especially ones that were a dime a dozen are worth next to nothing. If you see someone selling these, and without knowing their full history, assume they were already cherry picked and sent to repairers beforehand to confirm if they could have been economically repaired. If it's had a previously attempted repair this can often make your job many times more complicated due to missing parts or incorrect repairs, damage.It's best to have a reliable source, even better many of the same unit so you can draw parts and become familiar with one design. If you are planning to buy repair and resell on Ebay, while there are plenty of bargains but many sellers misrepresent what they are selling, so don't fall for "no idea if it works" kind of seller unless the price is right.Electronics repair is not exactly a blossoming industry, it takes a lot of dedication, patience and time. You could make good money on the side, but going from zero knowledge and trying for a full time income is unrealistic. You will have a better idea though when you have 20-30 successful repairs under your belt.Reality is you will spend many days of your time getting nothing for your effort, at least in the beginning.

author: Earl
author_rank: Contributor
timestamp: December 23, 2015, 07:15:21 am
content: Richard, thanks for that site address.Shock, thanks for your input, I am doing this on the side.Supply is enought to satisfy my needs, and I know they have not been worked on.I am power seller on ebay, so I am well aware of scammers.Thanks again for your input.

author: Earl
author_rank: Contributor
timestamp: December 23, 2015, 10:23:49 pm
content: I'm back sooner than expected.Just picked up Emerson VHS VCR/DVD Recorder Combo 4HD HiFi S-Video EWR20V5The DVD recorder side is working, but the 4 head hi-fi stereo side is not working.If anyone has worked on these, and has tips on what to check first, i would appreciate any helpful advice.Earl.

author: Richard Crowley
author_rank: Super Contributor
timestamp: December 23, 2015, 11:14:31 pm
content: Quote from: Earl on December 23, 2015, 10:23:49 pmWhat exactly does "not working" mean? There are probably 100 different symptoms that indicate different things to check.Does it power up and light up properly?Does it load a tape cassette?Does the head drum spin?Does FastForward and Rewind work?Does the pinch roller pull in and move tape in Play mode?Does it produce any kind of video output? Audio?You get the idea.....

author: Earl
author_rank: Contributor
timestamp: December 23, 2015, 11:37:37 pm
content: Thanks Richard you are right, my bad, I jumped the gun on that one.I was just thinking this item might have had a common problem,that someone might have been aware of.I am in the process of arranging my computer room, so I have space to work on items.I'll hook it up tomorrow and suss it out.Earl.

author: Earl
author_rank: Contributor
timestamp: December 24, 2015, 12:57:54 am
content: More info, I hooked power up to player,inserted tape,head drum was spinning, arms came out and took tape to drum, it played for about 10 seconds and then the power cuts off.Tried 3 times, same result.Tried the fast forward button before it cut off, nothing happened.Any ideas of the problem?Earl.

author: Richard Crowley
author_rank: Super Contributor
timestamp: December 24, 2015, 01:26:49 am
content: What exactly does "power cuts off" mean?Does the entire gadget (including the DVD side) just go completely cold dead?Is only the VHS side affected?Do all the lights (LEDs, indicators, etc.) go out? Or just the motors? The video and audio outputs?Start thinking in terms of more specific and comprehensive evaluation of symptoms."Power cuts off" is something we would expect to hear from a customer, not from someone trying to repair it.Do you have a meter that you can use to probe the power path?Don't suppose you have a schematic or any service information?How much work is it worth to revive something like this?

author: SeanB
author_rank: Super Contributor
timestamp: December 24, 2015, 05:22:56 am
content: MCU is detecting lack of tape transport moving, either because the gears under the deck have stripped, the clutch packs have popped apart or have worn, the reflective opto detectors are dirty or clogged or low emission, or the mode switch is failing or dirty.Hit play, press pause and it should stop there fully laced for around 3 minutes before stopping. that exonerates most of the mode switch. If fast forward or reverse does not have tape movement for at least 3 seconds then you have gear or clutch trouble. If it moves for 3 seconds then cuts off and ejects then the sensors are faulty.

author: Earl
author_rank: Contributor
timestamp: December 25, 2015, 04:32:34 pm
content: Richard, sorry I didn't give more info, I guess that's part of being a newbie.Answers to your last 3 questions 1/ no, 2/ no ,3/ it is worth it to me, as I am trying to learn how to repair these types of electronics.

author: Earl
author_rank: Contributor
timestamp: December 25, 2015, 04:43:07 pm
content: SeanB, Thank you for all that info, it really helps me a lot.I am researching online as well as asking you guys for help, trying not to be a nuisance in the forum, but I find some info on Web sites doesn't fully answer some questions I have.Thanks again, and merry Christmas and prosperous new year.Earl.