[HN Gopher] What to know to begin fixing amplifiers [video] ___________________________________________________________________ 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] ___________________________________________________________________ (page generated 2022-08-14 23:01 UTC)