Sony TA-N77ES Power Amplifier - Help with VU Meter

[Jeepnmon]

I have a Sony TA-N77ES power amplifier purchased from the original owner a couple of years ago. I used it a few times and it worked and sounded great. A few months afterwards, one of the power/VU meter needles stopped moving. Long story short, I had a tech look at it and he subsequently sent it to Instrument Meter Specialties for an evaluation, who determined that the cause was a broken wire in the assembly that basically cannot be repaired. My understanding is that this wire is beyond small (my term) and that a repair could possibly be attempted with no guarantee of success. I'm not a tech so my capabilities are non existent. I'm hoping that by posting this someone may have seen this issue before with this amplifier and has or knows of other possible solutions for repair. FYI, one of the steps I've taken is to post wanted ads for used working meter assemblies from parts units on various forums, websites etc. However, my sense is that that approach may be like finding a needle in a haystack.

Any assistance or ideas to help get this meter back working would be greatly appreciated! Thanks!

 

[restorer-john]

If the meter moving coil wiring is damaged, it will be a difficult if not impossible repair. The wire is hair like and they usually embed the wire in lacquer or a type of glue. It may be possible to carefully dismantle the movement, soak the bobbin in acetone to soften the potting/glues unwind and rewind the asssembly. Ensuring the two meters performed the same as one another would be a difficult task. If the wire is broken near the outer of the coil bobbin, repair may be an easier option- but the failure could be on the inner side where the tension is greater.

If it could be unwound, the number of turns could be measured/calculated and the matching meter measured as a reference.

The other issue to determine is the drive circuitry and whether the TA7318 meter drive IC is faulty and outputing DC which can happen. There is a series 1k resistor, but that won't save the meter. It's more likely a coil wire fracture/corrosion/glue failure, but don't rule out the IC either. It'd be a terrible shame to spend money on a new/salvaged meter, or a lot on a difficult repair only to have the same issue occur if the IC is the culprit and is perhaps intermittent.

It would be a repair where no guarantees of success could be made, but if it were mine, I'd definitely be doing it. The big N77 meters are beautiful- I never tire of them.

 

[Jeepnmon]

If the meter moving coil wiring is damaged, it will be a difficult if not impossible repair. The wire is hair like and they usually embed the wire in lacquer or a type of glue. It may be possible to carefully dismantle the movement, soak the bobbin in acetone to soften the potting/glues unwind and rewind the asssembly. Ensuring the two meters performed the same as one another would be a difficult task. If the wire is broken near the outer of the coil bobbin, repair may be an easier option- but the failure could be on the inner side where the tension is greater.

If it could be unwound, the number of turns could be measured/calculated and the matching meter measured as a reference.

The other issue to determine is the drive circuitry and whether the TA7318 meter drive IC is faulty and outputing DC which can happen. There is a series 1k resistor, but that won't save the meter. It's more likely a coil wire fracture/corrosion/glue failure, but don't rule out the IC either. It'd be a terrible shame to spend money on a new/salvaged meter, or a lot on a difficult repair only to have the same issue occur if the IC is the culprit and is perhaps intermittent.

It would be a repair where no guarantees of success could be made, but if it were mine, I'd definitely be doing it. The big N77 meters are beautiful- I never tire of them.

Wow, thanks for the detailed reply! I now have a somewhat better understanding of the possible issues with the meter. Seems like my options are to either invest in a repair process that potentially may not fix the issue, try and find a working meter from a parts unit, or settle for living with it - which I’m not ready to do yet.

A couple of questions. Is this an issue particular to this model? In your experience, would you have any particular recommendation/s of someone that could/would attempt this repair?

Thanks!

 

[restorer-john]

Wow, thanks for the detailed reply! I now have a somewhat better understanding of the possible issues with the meter. Seems like my options are to either invest in a repair process that potentially may not fix the issue, try and find a working meter from a parts unit, or settle for living with it - which I’m not ready to do yet.

A couple of questions. Is this an issue particular to this model? In your experience, would you have any particular recommendation/s of someone that could/would attempt this repair?

Thanks!

Hi,

Just saw your message.

I'd say the dead TAN-77es meter is a very rare issue.

Also, if it has been to a genuine metering instrument specialist and they have determined the coil is open circuit, it is basically dead at this point. If they haven't damaged it while inspecting, it may be salvagable.

I'm in Australia, so it may not be economic to ship a meter to me and back, plus having it repaired (if I can do it). You'd still need the meter back even if repair wasn't possible to keep the N77 looking normal and without a missing meter.

Say it could be repaired. You would need to recalibrate (pretty easy) the meter for level, when you got it back, but there's no guarantee the two meters would have the same ballistics. They may. They may not.

Put a search into eBay for the meter part number below, maybe write an impassioned letter to Sony's audio division in Japan and send them a physical registered letter with pictures of your "beloved Sony TAN-77es" and a picture of the dead meter asking if they can help or may have one deep in their parts store somewhere. Offer to pay them whatever it costs. I have often got things from Sony back in the day and even was able to obtain an original volume knob for Accuphase's first integrated amplifier made in 1972 by directly sending physical letters. The Japanese love personal contact.



If that gets you nowhere, pack the meter up, send it to me and I will do my best for you.

Cheers,

John

 

[JLElvira]

-Siempre gusta leer y que te ayuden para resolver un problema y aún gusta más cuando lo solucionamos, gracias por dar tu tiempo y conocimiento es grato tener ayuda,
_sony ta-n77es tiene su encanto y a mi personalmente me encanta