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sony ta-f555es II dc servo

Z

zolux

New Member
Hi,

I need some help to my recently purchased sony ta-f555es II. First thing what people do when they buy an old amp is get service manual for it and readjust everything to perfection. But I never had an amp that had adjustable DC servo.
So I have 2 trim pots, one to adjust the DC servo and one for the input FET stage's. My engineer knowledge says that, if I calibrate both in order to get zero V, then it will stay there no matter what. BUT, the service manual says that the volume knob should be in the lowest position, when I do the calibration, but if I do that, if I increase the volume the DC offset also grows. BUT if calibrate it in the highest volume, the DC offset does not change, while I change the volume.

Somebody please tell me, what the hell is going on.
 
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Hi - the service manual actually specifies to first set the DC balance of the main power amp section to zero (input FET stage), with the volume knob set to minimum, and then to set the DC balance of the preceeding V-I amp section (DC servo) to zero, with the volume knob set to maximum.

Alan
 
Thank you, you were right. Next time I should read every line of the service manual. Now the DC offset is less then 1mV in both channels.
BUT a new problem rises, actually old one, I noticed it before, but the DC offset had the priority. Transformer hum (E-I core). The good old 60Hz hum, but not coming from the speaker so not electrical problem. It's coming from the transformer itself. It's moderate volume, but kind of annoys me.
Any suggestion how to silence the old fellow? Maybe the transformer inside moved, while it was transit?
 
I can't help on the transformer problem I'm afraid - although I have several Sony ES range amps, none of them has ever had any issues with transformer hum. You could try tightening the mounting bolts, that might help (?).
 
It didn't helped, I think I will replace the transformer with a custom made toroid. The only question are the voltages... The datasheet does not tells the AC side voltages, only the DC ones. But I measured it under idle:
2x40,5VAC -->60V
2x40,5VAC -->60V
36,5VAC -->45V

soo 4x46VAC and 36VAC 300+W
 
Strange - most Sony (Bando) ES range transformers I've come across have been very quiet - I assume you already checked the rectification & main caps ?

As it happens, I've got it's little brother on the side here, ready for a refurbishment - theTA-F444ES II. Not sure what issues it has yet, beyond a bunch of fusibles that have all gone high.... and are 'choking' everything at the moment.
 
Yep, first I will replace most of the big caps and the 3 bridge bridge rectifier, and 2 TL071CP. But I can't work out the pitch of the leads in the Great Supply caps. They have 4 legs? Also what would be the best replacement for caps?
Because I already searched around, but most of the ( ELNA ) caps have 10mm pitch between the legs. And they seem to have more distance between then that.
 
Hi - I'd recommend you sort any 'problems' with the amp first, and basically service it fully before undertaking blanket re-capping or 'upgrades' of any kind - unless there's an obvious problem with the rectifiers, or IC's, I'd leave them well alone for now, they're unlikely to be an issue if it's playing.

If it's like most ES models I've seen from that era (admittedly only 4 or 5, but ALL were the same), there's a good chance it'll have a lot of off-spec fusible resistors present (they have a frequent tendency to go high with age), all of which should be replaced, ideally before further 'assessment' of what work it may or may not need. As an example, the TA-F444ES I'm working on at the moment has 14 out of 22 well out of spec., all of which look completely normal, but measure high or very high - I'll replace all 22 before further checks. Your TA-F555ES II has over 30 fusibles according to the manual........that's where I'd be checking / measuring things first.
 
Why is their not a Sony mfg forum?
Good advise Goldie99!!
The old ecap lead spacing is something you have to deal with, sometimes it is as easy as, just lead forming, other times if you want it to be perfect you drill holes in the pcb to fit the new lead spacing.
 
I will check those fuse resistors too, I didn't thought that those could be problematic. And the old caps ... well I will deal with them, when I get there.
Thanks for the replies!! I will post back my findings.
 
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