General Troubleshooting of SS Gear?

[birchoak]

I have read EchoWars's "So You Want To Repair Audio Gear?" and it is generous expert advice. After I read it, I wondered if there some sort of guide to basic troubleshooting of late 60's to early 80's solid state audio gear, mainly receivers and amps?

For example, when there's a low level, background hum or buzz from a receiver at 0 volume, does that usually indicate aged filter capacitors, barring bad equipment set-up, loose connections, etc.? What is usually is the cause of one channel completely gone in a stereo receiver or amplifier, beyond the obvious: balance knob dirty or turned all the way to right or left, volume pot dirty, other switches needing cleaning, blown fuse, RCA jumper(s) missing?

Allow me to go on: What seem to be the most vulnerable, failure-prone parts of most receivers/amps, in general? Things that see a lot of heat? Things with more than 2 moving parts in them, like relays and on/off switches? Electrolytic caps? The solder joints?

What components rarely fail in solid state electronics? For example, it seems like your average resistor, unless it has scorch marks on it or it's cracked apart, will last longer than anyone over 50 has to be concerned about. Output transistors mounted on big heat sinks seem fairly reliable to me unless the amp has been continuously overdriven or overheated through improper ventilation.

I'm looking for general information that would aid the everyman (not someone who's already an expert at this stuff) in at least troubleshooting common problems in amps and receivers. If that information can be relayed in simple terms that someone without a degree in higher electronics can understand, even better. This information would help people diagnose distorted bass on a Marantz 2230, for example, not how to re-wire the tonearm on a VPI Scoutmaster.

I know that I'm asking for a lot here, something that might not exist: a distillation of thousands of audio maladies into a simple "When this problem comes up, it's most likely this" solution, but it's worth a try. My personal goal is to save as many of these audio gems from the dumpster as possible. They are exquisitely crafted time machines, from an age that will never be repeated.

 

[kaplang]

Make sure it's plugged in.

 

[birchoak]

Zing! That's actually very funny.

 

[avionic]

Amazon --- TAB books --- Homer L. Davidson <--- Worked for this gentleman 74-78 until I enlisted in the air force. Local RCA dealer and repair shop. Davidson TV and Radio.

 

[gadget73]

resistors in a lot of older US gear are carbon composition, which are prone to drift and getting noisy. Japanese and European ones seem to usually be film that works very well unless roasted.

The last couple things I've had trouble with were faulty small signal transistors. One was cutting in and out, the other was making lots of hissing noises. The caps were overdue for replacement but were not actually causing obvious functional issues.

To be honest I think too many things are blamed on caps. Yeah they can and do fail, and they can cause problems, but they are not the source of all ills. Troubleshooting a fault before mass replacement is usually a good idea. I love my scope, it is probably the single best signal tracing troubleshooting tool I've ever owned. One of those amps with the transistors I actually skipped the troubleshooting because I had chased a problem to a bum cap on the tone control board a few weeks prior. I made the bad assumption that the noise issue that remained was probably caused by one of the other equally old capacitors dying. It was not.

 

[birchoak]

Avionic, per your suggestion I previewed Homer Davidson's book on Amazon and it looks great! I will track down a used copy and get busy with it. I like how he tells you finding the problem can be hard but to stick with it. Sometimes that's all a semi-talented amateur needs to hear to get back in the game. My personal Moby Dick is a Kenwood KA-7002 integrated amp. It has to be one of the best built things I have ever opened up and despite trying to fix it over a period of many years, it remains unfixed. I cannot bear to throw it away; even its solid milled aluminum knobs are beautiful, like the grille on a '57 Belair, and its insides rival the exterior.

Gadget73, it's nice to get more information on capacitors and while I do have a scope I don't think it's operating properly (grabbed it from sidewalk on trash day), nor am I entirely sure how to operate it!

 

[OMGCat!]

It's hard to make blanket statements on anything electronic especially ranging so many years. You can get drifting resistors, dried out caps, noisy transistors, tin whiskers in gm transistors, all sorts of other things.
Really the only things for sure is the pots are likely to be scratchy and it's probably full of dust and maybe cigarette residue.

I'd second Avionics recs on books to read and just read up. I'll add How to test almost everything electronic by Delton Horn. It's somewhat basic but it gives great insight into what test equipment you might want to look at buying and how to use it.
Once you go through some books and some repairs you can start using your built up knowledge to have an inkling at where the trouble lies in whatever it is your working on.
I'm no pro at all when it comes to this but after a LOT of reading on here and in books and a few challenging repairs I feel that I am confident that I can have a project end better than it started. I also had some awesome techs talk me through some of the challenges so don't discount making a thread about your Kenwood and seeing if anyone has any insight (I'd bet yes).

 

[birchoak]

Thanks OMG; I know what I'm asking for probably doesn't really exist but that Homer Davidson book looked darned close. I have had great success asking for help here at AK, too, of course. If I could find a local course in electronics I would enroll.

 

[ChrisMarantz]

Start leaning now about any part that interests you. Let the new information you learn lead you to new topics and keep learning and keep repeating.

Buy used equipment and attempt to repair it - failure is often the best teacher.

Keep at it regularly for the next 2 years and you'll find that you have scratched the surface enough to have some success and the picture will be much more in focus.

In 3 more years you should be able to handle most repairs - except for the ones you can't do. . .

By the time you think you know enough to tackle just about anything that comes along - fate will slap you in the back of the head and send you on your way.

It's a fun jouirney

Chris

 

[Alan0354]

Best weapon is to understand the transistor electronics. Get the book by Malvino. Learn the basics, don't guess what the problem. Take the time to calculate the DC voltages. There is no magic guide line how to troubleshoot and restore amplifier, knowledge is the best weapon.

https://www.amazon.com/Electronic-P...e=UTF8&qid=1505094893&sr=8-3&keywords=malvino

Buy used book for cheap.

 

[Alan0354]

For example, when there's a low level, background hum or buzz from a receiver at 0 volume, does that usually indicate aged filter capacitors, barring bad equipment set-up, loose connections, etc.? What is usually is the cause of one channel completely gone in a stereo receiver or amplifier, beyond the obvious: balance knob dirty or turned all the way to right or left, volume pot dirty, other switches needing cleaning, blown fuse, RCA jumper(s) missing?

I know that I'm asking for a lot here, something that might not exist: a distillation of thousands of audio maladies into a simple "When this problem comes up, it's most likely this" solution, but it's worth a try. My personal goal is to save as many of these audio gems from the dumpster as possible. They are exquisitely crafted time machines, from an age that will never be repeated.

A lot of the hum is due to grounding problem. Just because it is a perfectly working amp does not mean the ground in the amp is designed correctly......Yes, from major brands, high end brands. A lot of them are susceptible to ground hum just because you don't plug the device into the wall plug correctly. This is a huge topic on signal integrity and you might not able to fix it.

The wiring of my house is bad, both my Acurus and Nakamichi Stasis PA-7 hum like anything, there is nothing wrong with both of them, they are just not design well. There's nothing I can do in changing components to fix it. I would have to go in and redesign the grounding scheme to fix it.


I cannot stress the importance of understanding the circuit. Read the Malvino, the most useful part is the book explain how to separate the circuit into DC equivalent and AC equivalent. You analyzing the DC voltage, 95% of the time, you find the problem just by checking the voltage.


Piece of advice to someone that start out in this...................

DO NOT GET INTO HABBIT OF PULLING COMPONENTS OUT TO CHECK AND PUT THEM BACK IF THEY ARE GOOD.

DO NOT PULL OUT TRANSISTORS AND RESISTORS AND CHANGE THEM IF THE AMP IS WORKING.

Only thing that wear out are the big electrolytic filter caps. That you might want to change if it start bulging, leaking.......spill the beans!!!!

IF THE AMP IS NOT BROKEN, DO FIX IT. Study the circuit arming with the knowledge from Malvino, LOOK and STUDY the schematic, use the DC equivalent to calculate all the voltages at different points. Write the voltages down on the schematic and then measure the DC voltage and compare with the voltages calculated in the schematic. This will double check your knowledge and spot problems.

You don't know how many times I help finding problems here in the forum I never heard of the amp, never seen the amp or touch the amp. I just downloaded the schematic, spend 5 minutes to write out the voltages, then ask the person to measure for me. From the measurement, I analyze what gone wrong. I yet to ask people to pull out any parts before pinpointing the problem.


Think and observe a lot.....then do a little. Stand back and look at the issue at a distance first before you stick your hand into the amp. The mind is the best tool.

 

[Hipocrates]

Great stuff here.

By the time you think you know enough to tackle just about anything that comes along - fate will slap you in the back of the head and send you on your way.

priceless!... The fate has punch me a couple times and left me a nice black eye.

To the OP.
This is what I've found.

1. Learn to read schematics.(youtube, electronics dedicated websites).
2. Learn to see how that schematics apply to the units.(what is what)
3. Study your service manuals.
4. Study this ( http://www.talkingelectronics.com/Download/Malvino_Electronic-Principles.pdf )
5. Learn how to find transistors replacements.

Other toughs
./ With time you will find patterns on certain brands or models.
./ ''Preventive maintenance'' vs ''if not broken don't fix it" can open a can of worms. You will find very different opinions in this matter
./ Measuring voltages and understanding the unit is the way to go on diagnostics, (I usually start from the power supply section) but sometimes you will need to grab the shotgun and refresh the whole section or unit.
./ Fixing, recapping and reconditioning are different things.
./ Caps are the least faulty component.
./ Most of problems comes from semiconductors failures or numbnuts owners.

And the most important, training your mind to work ''on analysis mode" is the most important tool that you will have, and It will guide you to the best approach for your unit.

 

[avionic]

When measuring voltage..Always keep one hand in your pocket . Get yourself a good set of mini-grabbers for your multimeter.If you haven't already.. Drastically reduces the "Oops - there goes the MB smoke " phenomena.

 

[gslikker]

Make sure it's plugged in.

Based on MY experience, this depends on whether you are soldering at the device or not.

 

[kaplang]

Based on MY experience, this depends on whether you are soldering at the device or not.

If your soldering make sure the iron is plugged in.

 

[Roy Skinner]

Best weapon is to understand the transistor electronics. Get the book by Malvino. Learn the basics, don't guess what the problem. Take the time to calculate the DC voltages. There is no magic guide line how to troubleshoot and restore amplifier, knowledge is the best weapon.

https://www.amazon.com/Electronic-P...e=UTF8&qid=1505094893&sr=8-3&keywords=malvino

Buy used book for cheap.

$44.00 more $ to Amazon. Thanks guys. 3 books great deal.

 

[HVHiFI]

Lots of great info here and I concur knowledge is about the best tool you can acquire in electronics repair. Well knowledge and an oscilloscope.

The only thing I disagree with is that the large filter caps are the only ones that fail. I've found small <1uf capacitors on the input side of an amp blown, or noisy. I've seen power supply caps that tossed their cookies all over the board. Electrolytic caps and small signal transistors seem to always be the leading culprit of failure, amps that are noisy or sound like crap. Drifting resistors I would say is the next in line.

It's all about having fun and a rewarding experience when you fix something and get to enjoy it again. Read read and read some more.

 

[gadget73]

honestly I've had less problems with big filter caps than little ones in solid state gear. When the big ones go its easy to figure out. Either it has hum, or the cap explodes. They can start to go in ways that aren't quite so obvious but it usually doesn't cause the amp to completely not work when they get less efficient or go off value.

The little ones get noisy or they get leaky and cause all manner of non-specific stupid issues. Extra bonus points when the magic juice starts to leak out and corrode the board, thats a real fun time. The ones that control low voltage power supplies that run the remote control circuits and things like that are especially irritating because they can make stuff turn on and off randomly or glitch in not directly audible ways.

 

[birchoak]

Great feedback from everyone. I especially like Alan0354's advice to not pull resistors & transistors if the amp is working, and to think and observe, then do a little, always seeing the big picture and not making things worse.

My best troubleshooting and repair happens when I feel calm and optimistic, and I try to avoid sweaty marathon repair sessions with the device. And I do appreciate all the great reference materials people have suggested; my problem is that I tend to be a concrete thinker and my mind starts to lose its purchase with weighty concepts such as just how, exactly, a given circuit works. I could be overthinking things, too.

That said, I have successfully repaired turntables, receivers, cassette decks, and CD players. I even fixed a Luxman R-117 receiver (bad solder joints at the relays, if memory serves) and soldered my way to a working Lux (thanks to a tip here at AK, of course). I just wish it were easier sometimes.

My only goal is to be able to preserve and enjoy this beautiful, beautiful old gear and not have to rely on someone else or pay a small fortune [oxymoron alert] to get it working. Example: Paid $50 for a "working" Yamaha RX-500 cassette deck, but had to re-solder about 100 joints, adjust the motor speed, clean the heads, De-Ox all the pots and main motor, lube the capstan bearing, and tinker with the azimuth. Was it rewarding? Yes. Can I afford to pay someone else to do all these things for an Ebay relic? No. I do have to say the Yamaha RX decks are rather easy to take apart and put back together and things are well laid-out with plenty of room to maneuver; not so with an Onkyo.

Hipocrates: sometimes I am able to go in with a scalpel; when that fails I use the shotgun approach and more often than not the problem gets found/fixed in the process. I find myself trying to "think like electricity", or I'll ask myself, "What has to happen for this to work right?" I am frequently tempted to succumb to EPS (Exotic Problem Syndrome) when in fact I have forgotten to re-install the PRE/MAIN jumpers or unselect TAPE MONITOR.

I have had failures, too, of course. I smoked one of the channels in a Kenwood receiver (some tacky transitional model--very poor build quality and not a great loss to be honest), bungled a woofer re-foaming on a Paradigm Titan (glue EVERYWHERE), and to this day cannot get a Kenwood KA-7002 integrated amp to work properly.

 

[birchoak]

Update to my attempts at self-schooling: there's a gentleman calling himself 12voltvids on YouTube and a search for "NAD 7240PE bad channel" led me to his video of the same. While I don't agree with absolutely everything he does in the video, he sniffs out the NAD's problems in a tactile, almost cave-man approach (backed by sophisticated electronic testing gear, of course) that I can relate to. He gets the receiver back in working order before your very eyes and takes a bit of the mystery out of "fixing a bad channel." Especially interesting was a video on "Toshiba SA7150 No Sound Left Channel" : the SA7150 audio colossus has been brought to its knees by the failure of a single 22k resistor; that's right, one tiny, 10 cent part was the only thing holding back the monstrous wave of two channel awesomeness. And this guy finds it in 20 minutes. No wonder we hold master techs in such awe.