[HN Gopher] What to know to begin fixing amplifiers [video]
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What to know to begin fixing amplifiers [video]
Author : brudgers
Score : 42 points
Date : 2022-08-14 16:34 UTC (6 hours ago)
(HTM) web link (www.youtube.com)
(TXT) w3m dump (www.youtube.com)
| carlivar wrote:
| If you have a Marantz receiver/amplifier, this is also a good
| place to start:
|
| https://irebuildmarantz.com/classic/html/restoration.html
| latchkey wrote:
| One time I had an amplifier fail. I took it to a local repair
| shop that I found that had good reviews who charged me $150 to
| "look" at it. A month later, I called them to ask what the status
| was (because I hadn't heard anything from them) and they told me
| it couldn't be repaired. No other answer than that.
|
| That was a great $150 lesson...
| CSSer wrote:
| I had a similar experience once with a quadraphonic receiver
| from the 70s. When I went to pick it up the shop owner gave me
| the schematics and said he'd never seen anything that complex
| before. It was probably a dozen or more pages long. Even the
| AM/FM receiver dial pulley diagram was complex. I wanted to use
| it as a pet project but ultimately gave it away due to other
| priorities and lack of space.
|
| It wasn't completely broken though! Various features just
| didn't work. The whole system was insane. Each speaker cabinet
| had (iirc) 15" subs in it. Nowadays we have Atmos height
| speakers that are marketed as something completely new but
| these speakers had vertically oriented treble horns even back
| then. Modern speakers certainly have frequency response,
| efficiency, and compactness going for them, but to this day
| I've never heard any consumer system (I used to sell them in
| college) that loud. I rarely turned the volume past three (out
| of ten). I was only brave enough to briefly turn it up to seven
| once. When I did lights I'd never seen work illuminated. I felt
| Led Zeppelin in my chest.
| Gordonjcp wrote:
| I charge 300 quid to even look at a piece of equipment that's
| been "re-capped". Some people pay that, presumably because they
| realise that's the price of having the damage inflicted by the
| poke-and-hope brigade repaired.
| [deleted]
| [deleted]
| analog31 wrote:
| When I was doing repair, the shops referred to the charge for
| lifting your set onto their workbench as the "bench press." It
| was usually given as a minimum labor time charge, such as 1
| hour. You were doing well if you could get most repairs done in
| less than an hour. This depended on having both excellent
| diagnostic skill, and the experience to know what component was
| most likely to fail.
|
| I ended up in an Apple repair shop within a government agency
| that served school districts. Since we didn't need to make a
| profit, we skipped the bench press, and if your Apple needed 15
| minutes of work (typical), we charged for 15 minutes, while
| also letting you watch.
|
| The pinnacle was TV repair because TVs were expensive but
| cheaply made and relatively simplistic. There were not many
| different ways that they worked due to the evolution of cost
| cutting measures. There were also good published repair guides
| -- the Howard Sams "photofact" series.
|
| Stereos were not all that much more complicated, but a
| contemporary repair shop would suffer from lack of sufficient
| business to sustain a working knowledge of failures and
| repairs, and often obsolete or irreplaceable components such as
| output transistors. Paying $150 to sustain the shop, and learn
| that your set is unrepairable, are not far-fetched outcomes.
|
| Also (in the amplified musical instrument world that I now
| inhabit), there's a declining number of good techs. For one
| thing, those guys can make a lot more money servicing million
| dollar industrial or medical equipment.
| latchkey wrote:
| I was more than fine with the $150... which is why I paid it.
| I've had motorcycle shops do similar things and that's fine
| too.
|
| I think I was too subtle in my response though. The fact that
| they didn't call me after a month to tell me that it was
| broken beyond repair, feels kind of like they were never
| going to fix it.
| lttlrck wrote:
| The volume pot went in my 1992 Kenwood amp (18th birthday
| present). It crackled quite horrendously as they tend to do as
| they age.
|
| I took that amp back and forth to uni each semester carefully
| boxing it up each time, took it to Germany, back to the UK, and
| it's still with me in the US, albeit currently in its box.
|
| Huge sentimental value.
|
| A couple of years ago I found the (impressive) service manual for
| it that had the part number for the potentiometer. Unfortunately
| the part is no longer available, it has a special loudness tap on
| it. I replaced it with a pot without the tap, I never used
| loudness anyway. Works great. It's a brilliant amplifier.
|
| The service manual explains how to re-calibrate the amplifier
| current biases. So I checked it and it was still in spec.
|
| https://www.audioservicemanuals.com/k/kenwood/kenwood-ka/161...
|
| I also have a same era CD player that still works, I replaced
| it's laser maybe 10 years ago. Both purchased from Sevenoaks Hifi
| in Kent, by sending off a check in the mail.
| wszfahwbwbaha wrote:
| you have sentimental attachment to a...uh...amplifier?
| smackeyacky wrote:
| I can see this happening. My lounge doesn't look the same
| since my favourite (big) speakers got evicted in favour of a
| minimalist / soundbar thing that I hate.
|
| I just got very used to seeing (and hearing) those big black
| boxes and they have been in every house we lived in for over
| 30 years.
|
| If you're used to seeing (and hearing) something then having
| affection for those objects is quite common I would have
| thought.
| dmfdmf wrote:
| I haven't fixed an amp (yet) but I have been able to fix a few
| electronic doodads and boards using EEVBlog.com forums. Great
| resource if you are into electronic repair or troubleshooting.
| cannam wrote:
| As an ignorant person who occasionally repairs things, something
| I have often wanted is a handwavy guide to failure modes of
| components expressed in terms of their audible effect.
|
| What I mean is something that would help me to take a problem
| like "the bass keeps popping out and back in again in the left
| channel" and make a logical decision about whether to look first
| at the output transistors, amplifier bias current, some
| capacitors somewhere, the volume pot, quality of contacts for the
| input or output connection, or something else entirely.
|
| I'm not able to watch a video right now - does the "What Goes
| Wrong?" part of this go there? Is there a transcript or a source
| article?
| analog31 wrote:
| I've done a lot of repair in my day. I don't have what you
| need, but at the same time, my experience has taught me that
| 90% of "electronic" problems are mechanical in nature, such as
| switches, connectors, potentiometers, and so forth. Once you
| get into the guts of the amplifier circuit, it gets hard
| because that circuit is a feedback loop, so the signal can't be
| easily traced from one end to the other.
|
| In the evolution of my home audio equipment, the amplifiers are
| all Class-D IC's that are easier to replace at a board level.
|
| Prophylactically replacing things that might be broken can lead
| to worse problems, especially since a lot of older consumer
| electronics had relatively delicate single sided circuit boards
| that were easily damaged by desoldering.
| sitzkrieg wrote:
| came to post this, been my experience to a t. always start in
| places where things move, get plugged in, switches, look for
| exposed/funky looking traces/boards/connections. almost
| always an easy win once you crack the thing out (which can be
| a struggle)
|
| sometimes watching youtubers like bigclivedotcom cover
| failures of cheap electronics can show spectacular exceptions
| though. for some more realistic failures of common consumer
| hardware like laptops and cellphones (and general rework
| wizardry) Electronicsrepairschool is pretty hard to beat
|
| https://www.youtube.com/c/Bigclive
|
| https://www.youtube.com/c/Electronicsrepairschool
| dsr_ wrote:
| Well, if it's the bass alone and in the left channel, that
| strongly suggests a problem in the wiring of the left speaker.
| A continuity tester is your friend.
|
| If you get a crackling noise that changes when you change the
| volume, the volume potentiometer either needs to be cleaned or
| replaced. Similarly if the volume knob has ranges where the
| sound drops out entirely.
|
| If one channel doesn't work at all, you trace the signal path
| starting at the source.
|
| If nothing works, look for a fuse (and look for something that
| might have caused a short).
| tuatoru wrote:
| > A continuity test is your friend.
|
| Also a spray can of freeze (e.g. CRC Freeze Spray) is useful,
| and a jeweller's loupe (x20 magnification or so). If your
| phone takes good macro video, that can be really useful to
| look at several times (in the absence of a stereoscopic
| microscope).
|
| Contacts are the first thing to suspect with any fault. Check
| inside the plugs on the cables.
|
| For intermitttently disappearing and reappearing bass,
| though: probably the contacts are OK. Inspect (and if
| possible, re-make) solder joints in this part of the circuit
| - you may have a hidden dry joint somewhere. Then old
| electrolytic capacitors, especially tantalum ones, are
| sources of trouble.
|
| Of course if the amp has been in a house that's been hit by
| lightning, or where an arc welder has been used regularly,
| then the possibilities widen.
| qbasic_forever wrote:
| There's some great 90's and early 2000's era stereo gear that's
| basically free or very cheap at goodwill and thrift stores these
| days. I feel like right now is the time to snag good CD playback
| gear before it goes into the upswing in price as collectors
| items. No one is going to be building or selling 200 disc
| changers or high quality portable CD players any time soon for
| example, but CD collectors will love to have those things in
| decades to come. CDs in general I think are prime for a comeback
| like vinyl and tape have seen. Right now you can find them and
| the gear to play them for dirt cheap--it won't stay that way
| forever.
| a2tech wrote:
| I thought for sure it was going to be a link to Mr Carlsons lab:
| https://www.youtube.com/c/MrCarlsonsLab
| [deleted]
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