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Old 31st July 2009, 06:39 PM   #1
sangram is offline sangram  India
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Unhappy Sony TA-F222ES, need help

Hi

I have recently acquired a used Sony TA-F222ES (impulse buy, waiting for my F5s to take shape) that needs a bit of work. The unit is in mint condition except for the replacement of seven resistors in each channel, they look brand new and they've obviously been swapped in for the originals. They seem 'off', and I'd like to attempt a full restoration by swapping them out for the original values.

The resistors are base-stoppers for the output pair, and are marked as 100 ohm units. The bias test points across the emitter resistors register only 0.5mv, where they should be around 5mV according to the markings on the PCB. It is quite possible that the previous repairer misread the values and swapped in 10 ohm stoppers with 100 ohm units, and a similar mistake on the other resistors as well.

Also, he's used generic and cheap carbon-film units. the unit is in mint condition apart from this one glitch, and the unit is exhibiting some distortion at very low volumes (I'm assuming due to bias starvation), but it cleans up as one pumps it up a bit.

It would be great if i could get a service manual if someone has it handy, or even somebody with the same amp (also sold as the TA-500ES) could post a photo of it. It looks like a pretty well-built unit and I'd like to keep it (though I could swap it for something else, a Luxman or Sansui or a Nak).

Thanks for looking, and thanks for your help
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Old 31st July 2009, 09:52 PM   #2
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Default Re: Sony TA-F222ES, need help

Quote:
Originally posted by sangram
It would be great if i could get a service manual if someone has it handy...
I have sm for it, mail me.
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Non mai abbastanza...
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Old 1st August 2009, 07:45 AM   #3
sangram is offline sangram  India
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Thanks for the manual, aparatusonitus. The model is slightly different from what I have (I have the EsX, apparently it is significantly different), mine is a fully discrete design with lots of capacitors (Nichicon Muse, all of 'em) in the poweramp section and a different set of active devices, but there are sufficient hints to lead me to believe my initial suspicions are true.

I will not be able to claim the seller warranty if I change things in the amp, so I'll swap the unit for a different one rather than mess around with it as the exact values are still not known to me.

This is mine (or rather, like mine):

http://66.163.168.225/babelfish/tran...TA-F222ESX.htm
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Old 10th January 2010, 06:14 PM   #4
sangram is offline sangram  India
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Bumping an old thread - 3 questions:

1. All resistors are correct as per values, but no voltage across emitter resistors. When this test is conducted, no load is connected - though connecting one makes very little difference. I see about 0.3-0.4mV across the resistor, not the expected few mV. The amp works OK though, and heats up properly when pushed hard. Where should I start looking?

2. Output transistors on one channel smoked (my fault, while trying to troubleshoot) - 2SA1492/2SC3856 Sankens. Is the 1943/5200 a good substitute? They seem OK except the physical size, the newer ones are much larger and the amp requires a bit of mechanical dexterity to fit these properly, which I should be able to work out. Do the Toshiba devices have insulated bolt-holes? The originals did, and there's not much room for a bush in there.

3. The entire resistor compliment of the output section has been changed - it seems almost all the fusible resistors in the amp board fused at some point, so have been changed to some locally available carbon films. I suspect this will have some sonic impact, but the manual calls for 'fusible' resistors, I selected some Vishays (PPBCT series on Digikey). Would those work, or should I leave the current ones in?

Here's a schematic of the power amp section

Click the image to open in full size.
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Old 12th January 2010, 07:14 AM   #5
sangram is offline sangram  India
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I spent some time troubleshooting, and it seems the faulty part is Q409/459. I've put in all the voltages at the suspect part of the amp - can someone confirm?

I replaced the output pair with 1943/5200 and it works well enough, sounds a little better than the originals to me...

I'm surprised the thing is still playing, apparently without any distress.

Thanks for the help.

Click the image to open in full size.

And what would be a good substitute part? The specs say is is 200MHz, 140V, 200mA part with HFE ~300. NEC original, not available in my country. Since it's a CCS, can I get away with a slower device?

This is a slightly inferior device - Digi-Key - ZTX455-ND (Manufacturer - ZTX455).

This is the original part: 2SC3514 pdf, 2SC3514 description, 2SC3514 datasheets, 2SC3514 view ::: ALLDATASHEET :::

Last edited by sangram; 12th January 2010 at 07:42 AM.
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Old 12th January 2010, 08:02 AM   #6
Mooly is online now Mooly  United Kingdom
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If the amp works OK but there is no voltage across the output emmiter resistors that means a problem around Q309... your circuit is different to mine
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Old 12th January 2010, 08:24 AM   #7
sangram is offline sangram  India
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That would be Q411/461 in mine.

My problem part seems to be Q308 (your circuit). Q309 seems to be fine as there is a about 1.6V between emitter and collector, but I'll check again.

Q308 seems to be open circuit collector-emitter (no voltage at collector), but I don't know how to check this properly, in circuit or out. I'll try desoldering both and checking, may be I'll have to build a small rig for it?
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Old 12th January 2010, 10:50 AM   #8
Mooly is online now Mooly  United Kingdom
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If you are sure the amp plays OK with no audible distortion at very low levels then I would be careful and recheck your results. Using your circuit,

Check the voltage across R472, it should be around 0.7volts.
Does adjusting the bias pot not cause any increase in volts over the output emmiter resistors ? If not measure the voltage across C456 and see if it varies adjusting the bias pot.
Don't take too much notice of printed voltages... measure and confirm yourself that they are what you expect
The circuit shows 1.6 volts on emmiter of Q462 and 1.7v on the base for example which is wrong... the transistor would not be turned on at all like that.
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Old 12th January 2010, 01:31 PM   #9
sangram is offline sangram  India
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Thanks Mooly, I'll do that once I finish off restoring my friend's Luxman L-1 later tonight, or maybe tomorrow.

Offhand I do remember that between the maximum and minimum pot position, the variation in the voltage across the emitter was 0.1mV - it would change from 0.2mV to 0.3mV. also, at very low levels there is a bit of crossover distortion, plainly audible if you listen hard enough - but my speakers are <87dB/W, so you've to listen really, really hard for it. Once it reaches normal listening levels, there is no issue.
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Old 12th January 2010, 03:41 PM   #10
Mooly is online now Mooly  United Kingdom
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Check the above first... that volt drop across R472 and also check (measure ohms) R472
Wondering if someone has put wrong values in 1K instead of 100 ohm etc. Worth measuring them all around there, the values are all low enough to measure in circuit I would think.
I would expect audible distortion with no bias. The pot should swing it fairly high.

If the transistor is OK (Q461) and everything else is OK it has to be either a duff or incorrect value in the chain of components R474 D456 D457 R475 and the pot or unlikely C456 short circuit.
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