Please help me how to handle this repair shop

ychousa

Member
2007-01-08 10:41 pm
Hi, I'm really stressed out by this situation - I'd really appreciate your advice.
I had a repair shop to fix my Sony TA-F707ES integrated amplifier after it had sound cut problem from one channel. The repair shop said pre-amp parts needed to be replaced and they said they've replaced capacitors, transistors, and 3-resisters. They charged $250 for the job and received cash, which is their only payment method.

I was expecting the same clear sound without sound-cut, but to my disappointment, the sound from one channel was pretty different from the original sound. It was dull and the volume was small - if you know the sound quality of this amp, you know how good it is. But now it sounds like a $20 radio from one channel-apparently the one they changed parts. One strange thing is there's no heat from left-hand side when I check the heat on top of the amp. There was heat from all over the amp, but now the heat comes from right side of the amp only.

I would have disputed the charge, had they received the credit card payment, but I can't do that. Please experts, what do you think they did and how should I handle this situation? I feel like I've been ripped off. I don't know what they did to my lovely amp, but obviously the sound is totally different.

I wanted to ask experts before I go talk to them.

Could you help me to handel this situation?

I appreciate your help.
 

Jay

Banned
2003-02-11 9:02 am
Jakarta
The repair shop said pre-amp parts needed to be replaced and they said they've replaced capacitors, transistors, and 3-resisters. They charged $250 for the job

There is a thread where a mechanic in Tx abused client's Mustang. In electronics shops, at least in my place, the situation is much worse (and I think will be no different with your country)...

Caps, transistors and resistors in the preamp section is very cheap. The charge comes from the service, and there should be "standard" in your place. With $250 I could get a complete second hand Sony plus many others...

But the issue is whether they are honest...

I think the preamp part is cheap, but the amp part is expensive. The problem is when the mechanics pull out the good transistor parts (or any other parts in the box) and replace it with cheap ones...

The input transistors I believe the 5-leg dual transistors, 979 or something, which if broken I don't think is easy to find except by Sony partner.

You are in difficult position because you have trusted the mechanic...

If you want to go back, you can ask for the same part replacement (transistor), not just all purpose transistor like 2N5401 for example...

You can bring someone who understand electronics (which you might not have), but you can negotiate so your amp will sound good as before, by encouraging the mechanics to put in quality transistor, or fix other mistake he made, without additional cost as part of his client service. But it is up to you how far you want to "fix" the issue. Because being pissed off is intangible.
 
If I had just forked over 250 bucks of my hard-earned cash for a repair only to find that it clearly was incomplete (it would seem one channel has a bias issue or maybe more defective components lurking inside), that amp would be headed right back. I'm not sure about how it is in the 'States, but over here they'd have two more chances to get things sorted out, and if that doesn't work out either, you'd have to get your money back.

BTW, if memory serves these Sonys have a combined pre-power amp stage.
 
It is HIGHLY unlikely anything had to be done in the 'preamp stage' which strictly speaking does not exist in this amp. It is HIGHLY likely the problem is in the output stage or protection circuits, plus a number of places where contacts should be cleaned and soldering re-done.
In other words, that shop is bogus, like so many out there. Unfortunately this means tht now you have another problem - since they are incompetent to begin with, do not expect to have your problem solved by them. If they knew how to do it, they would have done it the first time.
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
I'm not familiar with the amp beyond just searching for info on it...

Would it be possible to show some clear photos of the output stage circuit board and/or any areas where work seems to have been done ?

Can you determine if the output transistors on the heatsink have been replaced. Do the device numbers match between channels ?
 

ychousa

Member
2007-01-08 10:41 pm
Hi, fellow members, thank you so much for your replies. I'm bringing back the amp to the shop, but I'm losing confidence in this shop- yeh, they might have taken some expensive parts from my amp and replaced with a cheap one. I'll try to take a picture after I get the amp back from them. But I think it was my fault to trust that shop. I can't believe here in the States, a fairly old business performs this cheesy job -either stealing any part or if not, making an equipment this much incompetent and saying the job is done. Just unbelievable.
 
ANy shop can mess up a repair, but any shop also deserves a chance to make it right, at least in my view. I ran a pro audio service shop for 30 years, just to be open about things, I report that.

Take it back and demonstrate the problem. I would hope your repair the first time came with a itemized repair invoice. I hope they didn't merely tell you to hand them an amount of money without one. That would tell you what they charged for labor, and what for parts.

I find it hard to imagine generating a $250 repair bill for a stereo amp. MY labor rate was $60 an hour, even if theirs was twice that, it still means they charged two hours. A few caps, resistors, and transistors can't cost much, not in a preamp.

In fairness if your cutout problem was an intermittent, those are the hardest things to find, because while the thing is working, the tech has no symptom to chase. My experience is that intermittent loss of signal - cutouts - is way more likely to be in the selector switching than in a transistor. The source select switching and the "tape monitor" switches in particular. And of course the volume and balance controls. After that I suspect solder. Intermittant components is down the list.

SO an explanation for the size of the bill ought to go beyond replacing a few preamp parts.
 

ychousa

Member
2007-01-08 10:41 pm
Is the volume really lower on the repaired channel. If you played a mono recording, is the image all to one side as if the balance were turned over ?

That would be a strange scenario.

Hi, Mooly,
Yes, the volume is low and one time the sound was cut. After I changed input line from CD to Aux, the sound recovered but still in low volume. The overall loudness decreased because of this-now I have to turn the volume nob to 12 o'clock to get the same volume that I had at around 9:30 before.

I've checked by turning the balance knob from left to right. My wife and I both confirmed that sound from the right channel that they must have worked is dull and has low volume. It's like the amp lost its strength completely and produce substandard sound.
 

ychousa

Member
2007-01-08 10:41 pm
I find it hard to imagine generating a $250 repair bill for a stereo amp. MY labor rate was $60 an hour, even if theirs was twice that, it still means they charged two hours. A few caps, resistors, and transistors can't cost much, not in a preamp.

In fairness if your cutout problem was an intermittent, those are the hardest things to find, because while the thing is working, the tech has no symptom to chase. My experience is that intermittent loss of signal - cutouts - is way more likely to be in the selector switching than in a transistor. The source select switching and the "tape monitor" switches in particular. And of course the volume and balance controls. After that I suspect solder. Intermittant components is down the list.

Thank you so much for your input with your expertise, Enzo. I more and more feel like I should have asked in these forums first before I payed for the cost. An expensive lesson learned :) I feel like I was definitely overchared by this shop, if not ripped off. It is my mistake to have had a fair amount of trust in this old business. I'll see how it goes after I bring this one back to them.
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
Hi, Mooly,
Yes, the volume is low and one time the sound was cut. After I changed input line from CD to Aux, the sound recovered but still in low volume. The overall loudness decreased because of this-now I have to turn the volume nob to 12 o'clock to get the same volume that I had at around 9:30 before.

I've checked by turning the balance knob from left to right. My wife and I both confirmed that sound from the right channel that they must have worked is dull and has low volume. It's like the amp lost its strength completely and produce substandard sound.

That all sounds very strange. I think all you can do is as others are now suggesting and at least let them have the opportunity of putting it right.

It would be really interesting to see just what has been done to the amplifier as it stands now because we are all guessing and drawing our own conclusions.
 

ychousa

Member
2007-01-08 10:41 pm
Can someone please give me some opinion how in the world this kind of dull sound can happen after changing parts in pre-amp such as transistors, capacitors, and resisters? Are those that much critical parts to affect sound quality to this degree? That question has been lingering in my mind from the day that I picked it up. This is a 50+ year old electronics repair shop, specializing in vintage amp repairs. I mean, is there any possiblity they might have taken critical parts from my amp for their own use? Or some sort of soldering could not be done correctly? I really can't understand how this could happen. (They said they got the parts from distributors not from Sony because this is an old model when I called before pickup.)
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
Can someone please give me some opinion how in the world this kind of dull sound can happen after changing parts in pre-amp such as transistors, capacitors, and resisters?

I can't I'm afraid. In isolation, swapping any of those parts for normal commercial grade replacements would not alter the sound quality at all.

You did mention that the repaired channel runs cold... now I had a quick look at the circuit yesterday and it uses FET's as the output transistors, the 2SK1529 and its complement. I have a recollection (you would have to check) that these are near unobtainable. Is it possible they have fitted a standard bjt device in place of the FET's. That's not as crazy as it sounds because the Sony diagram (the one I have anyway) shows them drawn more like conventional transistors than FET's... and it might work after a fashion.

Its all guess work unless you at least have a peek under the cover to see.
 
One of the parts they installed was defective, or they installed a transistor backwards, or a solder joint was shorted to another with excess solder, or a printed circuit trace was cracked, or they tried to clean some contacts and were not thorough (so it stirred up some dirt on the contacts), or a wrong value part was installed, or...any other number of things.
 
I know this amp fairly well, still own one.
They have a curious bias circuit which can be tricky to adjust, but more importantly, the output stage is a 'MOSFETlington' with two MOSFET stages. The first one are 2SJ313 and complement (don't remember off-hand the number, 2SKxxx), and these are in a fully isolated TO220 case. It appears they sometimes mechanically fail internally, resulting in intermittent or odd behaviour with low and crackly output. It is at first listen similar to an intermittent contact in the speaker relay. What happens is the driver stage starts driving the output pairs directly through the protection zener, and the bias current is nonexistent. Sometimes tapping the heatsink will restore normal operation.
The main problem with repair shops is getting parts on the cheap = fakes. It is likely they installed fake output or driver MOSFETs (drivers are in particular suspect as they are VERY expensive, up to twice the price of the outputs, and are to my knowledge obsolete). If one knows what they are doing, using an IRF610/9610 pair is possible with added insulation to the heatsink and modified bias circuit (the Vgs tresholds cannot be reached with original component values).
The circuit itself is odd that at one point if you go to a higher bias value, it 'folds back' and the bias voltage collapses. It is quite finicky and may even do this when a different Vgs grade of the driver is used.
 

ychousa

Member
2007-01-08 10:41 pm
I know this amp fairly well, still own one.
They have a curious bias circuit which can be tricky to adjust, but more importantly, the output stage is a 'MOSFETlington' with two MOSFET stages. The first one are 2SJ313 and complement (don't remember off-hand the number, 2SKxxx), and these are in a fully isolated TO220 case. It appears they sometimes mechanically fail internally, resulting in intermittent or odd behaviour with low and crackly output. It is at first listen similar to an intermittent contact in the speaker relay. What happens is the driver stage starts driving the output pairs directly through the protection zener, and the bias current is nonexistent. Sometimes tapping the heatsink will restore normal operation.
The main problem with repair shops is getting parts on the cheap = fakes. It is likely they installed fake output or driver MOSFETs (drivers are in particular suspect as they are VERY expensive, up to twice the price of the outputs, and are to my knowledge obsolete). If one knows what they are doing, using an IRF610/9610 pair is possible with added insulation to the heatsink and modified bias circuit (the Vgs tresholds cannot be reached with original component values).
The circuit itself is odd that at one point if you go to a higher bias value, it 'folds back' and the bias voltage collapses. It is quite finicky and may even do this when a different Vgs grade of the driver is used.

Hi, ilimzn,
Thanks for your great, detailed info. Frankly, I don't understand most part of your post, but can I interpret it as this amp is likely to cause more trouble in the future compared to other vintage amps? :)

From their word, they replaced transistors, capacitors, and 3 resisters, not drivers or output. Does this make sense?
 
This amp does not even have a pre-amp in the traditional sense.
Basically just a volume control straight into the power amp Input stage.
Changing parts in the pre-amp = really? What parts exactly!!
Ask them exactly what parts they changed, and what they used as replacements? Good mechanics show you the old parts.
Ask for references from the schematics, based on the service manuals that we all can get at hifiengine and have reviewed. There is very little for us to analyze without knowing this information.
Ask for the THD tests, it has 0.004% 10W 8 ohms. It is a very low figure
 
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All you have to do is take it back to the shop. Tell them you had brought it there in the first place because you had heard they were the best and unfortunately the repair doesn't seem to be working properly. You might mention that you bought it based on the MOSFET design, but no more than that.

The other method is to scream at them and hold your breath until you turn blue in your face.

Your choice.
 
...Or ask here about a reputable shop in your area or close enough you can ship it fairly securely, where they will do a proper job on it.

As to your question, what they changed is really of no use as there are hundreds of resistors and capacitors in there, tens of transistors. Schematic designators R(number) C(number) etc would mean something. THe service manual is available on-line for free, so no guesswork should be involved. Or - you should be given the old parts.
This amp is as reliable as any other quality component in my view. The problems it has have nothing to do with the design, and I have yet to learn of a vintage amp that has NO problems at all. It happens. Normal for a device built out of hundreds and hundreds of parts.
 

LiquidMids

Banned
2013-05-30 12:55 am
I have been enjoying my 707ES for about a year now.

I have been all through it, and there are no combined or darlington stages, op amps,

or anything that can't be matched anywhere in the audio circuit of this amp. It is a

fine amp for sure. Only the first input pair is a 979 5 pin like mentioned, basically two input

mosfets matched in an IC. - this is common in a lot of amps, even high end.

Sony's TA-N500ES (and others) do, in fact, use darlington (combined package) outputs.

You really gotta watch the model numbers with Sony.. only a few models are really good..

This amp has individual - single die output mosfets.

Two pairs per channel - j200A and K1529A

I would not trust that shop with my baby again..

An 808 just sold on flea bay for $1075!

Message me and we can work out a fair repair deal if you want. I have my own personal repair

bench, repairing amps has been my hobby for over 5 years now.. The hard part can be getting

the pairs closely matched.. sometimes it takes some extras.. I can tell you how to verify with a

multi-meter across each output resistor that the pairs are matched so you can check my work.

Your ears will know though!
 
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