Sony V-Fet Amp TA-N7B problem

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#41
Netlist said:
Bernhard,
do yourself and that beauty a favor and check the solderings on the driver boards. Sony is well know for invisible bad solderings.
Also, tighten the screws of the output transistors to make sure the collectors make good contact.

/Hugo
Click to expand...


Ehh, ahum, err, first thing I did with mine was putting it in the dishwasher. No special precautions, just the way it is. Let it run through an "economy" cycle, and it comes out as new. This is really unbelievable, so clean, factory new (had no scratches, only very dirty and smudgy).

Switched it on, no problems whatsoever. Because of the hot drying cycle, and the special ingredients in the diswasher tablets, there is NO residue on the pcb and other internal parts (that's also why those glasses come out sparkling).

I needed to actuate the power switch a couple of times to get it switching with a good 'feel' but that was all.
I have dishwashed lots of amps and test equipment, never a problem.
But the machiune smells funny afterwards, you need to run a cleaning cycles afterwards to keep your OSH happy.

Jan Didden
 
#43
Netlist said:
ROTFL

What about shiny front panels?
Also, does the brand of the tablets effect the sound? :devilr:

/Hugo 🙂
Click to expand...

Front panels come out like new. The TA-N7 has black painted cans over the transformers and the supply caps. They looked like they were painted yesterday.

Tablets: I used PowerTabs, with a red blob in the middle. Results are a more powerfull, but at the same time warmer rendition of the sound field.
For test equipment I use blue tabs, which seems to improve the calibration a bit.

Jan Didden
 
#46
Nice to see you have fun with my thread 😀

I have another candidate for repair, the pre-amp TA-E7B.
Somebody removed the solder on all three legs of two grey little transistors and made bridges with two wires over a distance of approx. 5 cm.

No idea why. I even do not know what it does in the circuit.

Also could not find anything that would not work on the pre-amp.
It is located on the small board with VU-meter and tone control.

Schematic any body ? 😀

This pre-amp is ugly.

I will continue with the power amp repair tomorrow when shops are open and hopefully I get those resistors.
 
#49
janneman said:
Ehh, ahum, err, first thing I did with mine was putting it in the dishwasher. No special precautions, just the way it is. Let it run through an "economy" cycle, and it comes out as new. This is really unbelievable, so clean, factory new
Click to expand...

Hi Jan

Are you note concerned , with eventual residues of lead (from the solders) that can be eventually stay in the dishwasher...and may damage your health.:att'n:
 
#50
Works everything on the power amp now. 🙂

Bias is 45 mV on both channels.

I changed all 9 safety resistors on each driver board, 7 per board were defective.
Like 220 measured 350 or 870 or so. 47 measured 100.

Also changed the 220/50 and 4,7/100 lytics for 105° Panasonic.

Tomorrow I will start with the preamp.

Thanks for the help to everybody !
 
#51
Hi Jorge,
The lead concern is overblown, it gets washed out. I wouldn't drink water from lead pipes as the lead is dissolved in the water. For over 30 yrs I have breathed lead - tin fumes. I am negative for heavy metals as I have requested to be tested specifically for lead and tin. Either that or my family doctor is lying to me.

-Chris
 
#52
I'm currently working on a similar problem. An old Hitachi HMA-8300. Many safety resistors out of spec, replaced a lot already but still no sound. Oh... put it in the dishwasher and came out like new apart from some minor problems.

If I fix it I'll start a new thread about it. I've got a feeling it's quite an interesting amp.
Edit: schematic anyone? :angel:

/Hugo 🙂
 

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#54
Hugo,

this amp is stuffed with 2SK/2SJ mosfets 😀

Supply rails ok ?
Cleaned the relais ?????????
DC offset before the relais ? Maybe protection active ?


Jan,

did you check all your safety resistors ?


How would you rate the TA-N7B compared to other amps ?


I wonder how many amps are around with parts far out of specs, and the amps running in whatever class 😀

Just had a quick look at the preamp, somebody made bridges from signal input to signal output on the Hi/low filter board. Maybe bypassed only the low filter because the high filter and tone control works.

As ugly as it is, it got three big fat ALPS pots, a big labyrinth with lots of secret chambers stuffed with pcb...

One channel has 140mV offset and the power amp does not switch on the relais when connected via DC input...
 
#57
The bypass was made because the low pass switch had some contact problems. Some contact spray and that thing worked...

The preamp uses a pair of 100µ/6V Tantal drops back to back, bypassed with 15n film as coupling cap. 😀

All Tantals shorted dead.

Still offset on one channel inside the amp which means something wrong.

By the way I just found Tantal coupling caps ( no back to back, not bypassed with film ) inside a Revox B739 Tuner Preamp that also suffers from multiple problems.
 
#58
Sony and Hitachi schematics are still on their way.
You'll have it one of these days, promised. Perhaps even for free or the cost of the copy.

Tantalum's...they were widely used in all kind of gear in those days. They now prove they couldn't stand the test of time.
Dead shorts are very common.

/Hugo 🙂
 
#60
Bernhard said:
[snip]Jan,

did you check all your safety resistors ?


How would you rate the TA-N7B compared to other amps ?
[snip]
Click to expand...


Bernhard,

No, I haven't changed anything. When I got it, after running it through the dishwasher I checked the offset, which was 3 or 4 mV, and tuned up the bias, that was all. I have used it as a replacement amp while I was working on my main amps.
It wasn't as detailed as that one, but quite acceptable, I'm sure that after a few days I wouldn't notice it anymore.

Jan Didden
 
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