How far do you go making repairs on a friend's nostalgic HiFi amplifier? - Page 1
Forum section: electronics / repair

author: peteb2
author_rank: Regular Contributor
timestamp: October 30, 2017, 03:08:16 am
content: So this is a two fold question. Friend comes to me and talks of his old Yamaha A-460 he'd had since a young chap. He spent hours listening to all his music back in the day and now associates that music with the memories and "how the amp sounds"....First thing, the unit was DOA and the owner a little miffed because not too many months ago he'd had dug it out and taken it to a major repair company 'to check it out" for what became AUD$200 in work on it.So as a tech and huge hobbyist in HiFi electronics i agreed to see why it was now silent... I noticed a brandnew 3 pin mains plug and that was all really.Upon opening the unit (it guess it would have been a reasonable spec'd amp in it's day) i was stunned at the thick coating of rosin all over the huge FR-2 type PCB which had dried so brittle in patches that it had turned into little mounds of dust. The input switch selection of the A-460 is via mechanical flexible looms that 'tweaked' the board ever so slightly and hence the rosin dust.... i guess.One channel had obviously received new output transistors in it's life because there were the plenty of fat finger prints all over the area on the PCB in a now very dried turning-a dull yellow-colour heatsink compound. Whomever did the job sure came from the school of "the bigger the job the bigger the gobb" thinking. Compound was everywhere....Back to the fault and it didn't take long to notice the speaker protector circuit was activating and just about as long to discover the reason way a case of hundreds of DRY JOINTS...Even on the + lead of the main bridge rectifier you could see a huge black patch of melted copper and missing solder....This PCB appeared to me to have probably not spent long enough in the flow solder tank (i guess that's how how it was done) and it really would have been great if Yamaha had sent it though a rosin wash but i digress..So all these years latter and the solder joins were cracking undone by the look... The picture shows one original factory output transistor, the centre pin of the three was completely adrift!I re-soldered the worst and made the amp come back to life but seriously, almost the entire board would benefit from some work. Even the output transistors that were part of a repair looked terrible in the soldering. It would be good practice to check quiescent current too...Here's where it gets questionable. The owner really wants this unit fully 'restored'. That says i suppose, that i'd clean everything of the rosin re-solder everything, replace the electrolytics and reset the quiescent current... but is it worth it....? My suggestion was that now its working again enjoy it as it is and put the $ towards a better more modern amp or a proper 'Old Skool" high value unit....What would you do?

author: DrGeoff
author_rank: Frequent Contributor
timestamp: October 30, 2017, 04:24:53 am
content: Quote from: peteb2 on October 30, 2017, 03:08:16 amMay have been wave soldered, which was used a lot back in those days. A wave of flux followed by a wave of solder.This is not uncommon for a lot of old equipment, particularly as a lot was built with single-sided PCB's, and the joints crack easily over time as the solder goes brittle.I'd suggest resoldering all the joints. Usually does not take too long.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: October 30, 2017, 04:56:57 am
content: Only your customer/friend can answer that question. I would probably rework it, but I am retired and don't have to pay any bills doing this stuff. Tell your friend how much it would cost to do the restoration for a stranger, then give him the friend price if you want to give him a break, and see if he thinks it is worth it. He may surprise you.This is much like those guys who pay tens of thousands of dollars for restored automobiles. It is clearly worth it to them, but it really makes no sense to spend much twice or more the price of a new car for something that even if perfectly restored will still be inferior to the current product.In cars it is old technology like points, drum brakes, carburetors and the like which are nowhere close to current products, in stereos it is linear power supplies and amplifiers, analog tone controls and drifty tuners. But none of that overpowers the nostalgia for the old gear.

author: Armadillo
author_rank: Super Contributor
timestamp: October 30, 2017, 10:08:30 am
content: The pertinent technical stuffs would be if the quiescent bias current, power, distortions, sound quality are all in order, and if so, no need to overly drag on how dirty, oily, greasily and etc. on the board or solder work that repeatedly occupies so many lines of texts. If there is no substantiation, why do a recap?If it has not corroded up until now then it is apparent that the rosin flux had done its job. A general cleanout and return it to your "FRIEND" with some cans of beer and play social catching up with him, would be a nice thing to do. Cheers;

author: amyk
author_rank: Super Contributor
timestamp: October 30, 2017, 10:31:18 am
content: A hot air gun will make reflowing all the joints much faster and easier.

author: Seekonk
author_rank: Super Contributor
timestamp: October 30, 2017, 02:52:57 pm
content: That brings back memories. Fixing audio equipment in the early 70's put me through college. I used to fix a lot of stuff after other "professionals" worked on them. I even got tips. 80% of people are incompetent at their job, be it doctors, engineers techs, whatever. Around that time period there were these bias diodes (two or three in a series package made by ORIGN. They would intermittently open taking the outputs.

author: Armadillo
author_rank: Super Contributor
timestamp: October 30, 2017, 03:44:45 pm
content: Quote from: Seekonk on October 30, 2017, 02:52:57 pmIntermittent problem has always been a nightmare to repair. Nowadays these ceramic smd chips also like to play hide and seek too.

author: cvanc
author_rank: Frequent Contributor
timestamp: October 30, 2017, 04:02:30 pm
content: It may or may not relate to the OP's issue but I'm currently working on a vintage Yamaha receiver and it, too, has an unusual amount of cold solder joints. More than I usually see in old audio gear.

author: coromonadalix
author_rank: Super Contributor
timestamp: October 30, 2017, 10:33:31 pm
content: I have an old Sony cassette tape from the Esprit series, TCK xxx, life time heads, closed loop capstan motors, a very well bild mechanism, Dolby B and C, bought for 200$ used, at that time it costed much more $$$ to get them.I reworked all the psu parts / capacitors regulators ... the noise floor has dramatically dropped, sure its an old beast, and i slowly convert all my casettes to mp3, but the sound of it is perfect, i have jean michel jarre concerts on metal tapes, they still sound perfects lollBut sadly one day i'll have to toss it away.Tossed a Super VHS not to long ago, the last model NEC ever build, incredible quality at the time, i had super beta video from toshiba, boy they were heavy and very well build.I love old systems, they were relatively simpler to repair and keep working for a long time, with Sony i could find 10-15 years old parts few years back.Had even a Realistic (Radio Shack/Sanyo) tunner amp, 100w rms stereo sound system, made a terrible mistake to give it for nothing.If you can repair old stuff and you love them, keep themA friend of mine has rebuild my old Phillips 1954 multiband lamp radio of my deceased father, cleaned and restored the chasis frame, found a original wood casing, changed the caps with the original models, new lamps, new dial cord, the only thing damaged are two knobs (cracked shaft inserts), but usable. It still works today, with a very good antenna, im able to listen many countries on european continent, i'm in Canada lolll

author: cdev
author_rank: Super Contributor
timestamp: October 30, 2017, 11:39:08 pm
content: I'm like your friend, I am kind of emotionally attached to my most recent iteration of old audio equipment.NAD receiver, Sony cassette deck.. etc. Both still work great.I have done my best to keep the insides clean and do preventative maintenance.. also use them..

author: BMack
author_rank: Regular Contributor
timestamp: October 31, 2017, 05:50:58 am
content: I repair electronics for work...I try not to let too many people know what I do because everyone becomes a friend when they need something fixed and because they're friends they don't want to pay going rate. Fully service it, replace all capacitors? I'm not doing that for less than $50/hr, if it's actual troubleshooting $70/hr.If it's a TV and it's just replacing a board, or something simple and under 20mins buy me dinner or some beer. Though that changes on how good of a friend or how you ask. I've literally had "friends" that started a computer/phone repair "business" in their home ask me how to troubleshoot their TV...so what you want me to do is teach you how to repair TVs so you can try to compete with my shop and undercut my pricing because you have no overhead? Yeah, not going to happen.

author: tooki
author_rank: Super Contributor
timestamp: October 31, 2017, 06:53:04 am
content: Quote from: amyk on October 30, 2017, 10:31:18 amThat is terrible advice.Old PCBs, especially FR-2, have fairly poor bonding of the copper to the board. The longer you heat it, the weaker the bond becomes. Using hot air for these large solder joints is gonna take a LONG time, far, far longer than a soldering iron. You wanna be in and out, not hanging around for minutes and minutes of unfocused heating.Besides, the joints probably can't be simply reflowed; old solder doesn't like that. It will probably be necessary to flow on some fresh solder anyway.

author: Seekonk
author_rank: Super Contributor
timestamp: October 31, 2017, 08:13:55 pm
content: That certainly is bad advice. I've had joints where the lead is poisoned from heat and it takes some effort to get them resoldered when plating has come off component leads."Tossed a Super VHS not to long ago, the last model NEC ever build"I still have a professional SONY Super Beta HiFi GCS-50. Think that was the best one they ever built. Amazing what it can do for its age scroll forward and back frame by frame with ease.