Need help about understanding power transformer of a cassette deck, please.

[vince666]

First off, I hope i am posting in the right section, otherwise it'll need to be moved elsewhere...

Hi my friends...
I have a question to ask you, to help a good friend of mine who doesn't know english and then he cannot visit any forum where english is the official language...

This friend of mine has got a Sony TC-K333ESA cassette deck (japanese domestic model identical to the TC-K970ES) for very cheap and in like new shape save for a serious problem: the previous owner didn't realize it was a 110V japanese model and so, with a plug adapter, he directly attached it to the 220V here in Italy and then he burned the AC transformer.

So, my friend would need to get a suitable transformer for this monster deck... he will get a custom built one (not cheap!) but, to do so, he needs to exactly know the voltages which come out of the secondary windings for this deck.

I am attaching two pics taken from the service manual...

first one is from the block diagram (and maybe not useful but I attach it anyway)



this second one is taken from the actual schematic and should be more useful...



as you can see, there are 3 groups/connectors of 3 wires each, coming out from the secondary winding of the T701 power transformer:
(from top to bottom)
CN704: Orange-Brown-Orange
CN705: Blu-Grey-Blu
CN703: Red-Black-Red

There are a few voltages mentioned at these wires but, since neither myself nor my friend are that great in reading schematics while being 100% sure we got it right, I am asking here if any of you experts can explicitly tell me which are the voltages related to any of the aforementioned 9 coloured wires coming from the secondary windings...
This way, my friend would be able to provide the needed data to those who can custom build a suitable replacement transformer for him and to bring this nice deck back to life.

I also wonder (but this is more a curiousity of mine) what does it mean at the aforementioned connectors that some pins are filled in black ink while the others don't.

Of course, any further hints/advices you might consider useful to get the work nicely done (and/or to understand the situation a bit better) would be really appreciated.

So, please, feel free to explain the easy/detailed way just like when you're trying to explain something to a totally ignorant guy about the actual matter (i.e. myself )... also because I will need to be able to explain it to my friend or to at least translate to italian for him to understand.

Thanks in advance,

Cheers,

Vince.

 

[vince666]

if it might help, here is a bigger picture zoomed in just at the secondary windings zone

 

[mlucitt]

Based on the schematic, I can tell you the voltages measured from the secondary windings; not necessarily the designed voltages. But you need to know the power rating of each winding which determines the power rating of the whole transformer. If your friend still has the transformer, the transformer winders will likely be able to determine the power rating in VA (Volt Amps) of the transformer.
CN704: Orange-Brown-Orange -- 28.4VCT (in other words +14.2V and -14.2V with the Center Tap not carrying any voltage because it is grounded)
CN705: Blu-Grey-Blu -- 4.3VCT (this is a filament voltage likely for the fluorescent display and the CT is not grounded.
CN703: Red-Black-Red -- 26.2VCT (+13.1V and -13.1V with the Center Tap grounded)

Good luck

 

[AngrySailor]

One has to wonder what else is fried with over double voltage applied... did any of the fuses open? Even then damage may be more...

 

[mlucitt]

One has to wonder what else is fried with over double voltage applied... did any of the fuses open? Even then damage may be more...

I think the fuse would have opened if the voltage disaster was reversed (240V unit supplied with 110V power), but not the other way around.

 

[AngrySailor]

I think the fuse would have opened if the voltage disaster was reversed (240V unit supplied with 110V power), but not the other way around.

Yeah that’s kinda what I was thinking too... fuses would be double ratting for half the voltage...

 

[vince666]

Based on the schematic, I can tell you the voltages measured from the secondary windings; not necessarily the designed voltages. But you need to know the power rating of each winding which determines the power rating of the whole transformer. If your friend still has the transformer, the transformer winders will likely be able to determine the power rating in VA (Volt Amps) of the transformer.
CN704: Orange-Brown-Orange -- 28.4VCT (in other words +14.2V and -14.2V with the Center Tap not carrying any voltage because it is grounded)
CN705: Blu-Grey-Blu -- 4.3VCT (this is a filament voltage likely for the fluorescent display and the CT is not grounded.
CN703: Red-Black-Red -- 26.2VCT (+13.1V and -13.1V with the Center Tap grounded)

Good luck

Thank You Very Much.

Of course, I am so ignorant about these electrical matters that I am not able to fully understand myself what you kindly mentioned... but, hopefully, my friend will understand it better than myself if I will simply translate it to italian for him... then, I will just literally translate it to him.

About power ratings, I believe my friend just has some idea or knows how to discover the minimum required power from the power transformer (is it risky if he will simply get it more powerful than strictly needed? but this is a doubt of mine)...
The original (burnt) transformer isn't easy to analyze because it's one of those beasts enclosed into a metal box and filled with some kind of cement, then it's not easy to open it and check the original windings directly.

And, about the damage on the deck, most likely it's only the power transformer which got broken... in fact, the fuses, diodes (ect) which are just after the secondary winding did not blow... his idea is that the thermal fuse inbuilt into the power transformer is what really got broken but he needs to get a new custom built transformer anyway.

So, thanks a lot... will start forwarding these informations to my friend and, if needed, will return here asking about further details.

You guys rock!


PS: and so the black dots at the connectors on some of those wires mean that the voltage is negative?
Isn't it only AC, then? (from this P.S. you will easily realize even more how I am ignorant about electrical matters! )

 

[AngrySailor]

It’s got a voltage selector switch, you sure it’s 110v as there’s no selection for that?

 

[vince666]

It’s got a voltage selector switch, you sure it’s 110v as there’s no selection for that?

that's the same question I had also asked to my friend... but that deck is without voltage selector as it must be a Japan-only version.
So, you see the voltage selector there in the schematic only.

That said, maybe it's my mistake in saying just 110V...
The actual voltage, then, is the one they use there in Japan, whichever it really is.
But, since my friend is going to get a new power transformer, he will directly convert the deck to EU/Italian voltage so he needs to just get the secondary voltages right.

But I don't know if they do also exist versions of that same deck with an actual voltage selector... maybe yes?

 

[mlucitt]

Japan is 100V.
Sorry, I forgot your question regarding the dots. The dots are the connector keys. They are marked this way in the schematic to correspond to a feature that keeps them from being inserted backwards. Think of the black dots as "Pin 1".

To better explain, the secondary winding can be a single coil of wire and the voltage would be referenced to zero on one end, for example Yellow = 0V and Yellow = 24V. Or, the secondary could be wound in such a way that there are two coils connected together in the middle, so the coil is "Tapped" at 0V and the two ends have equal and opposite phase voltage on them. for example Yellow = -24V, Yellow with a Red stripe = 0V, and Yellow = +24V. When the middle of the two coils (or Tap) are connected and grounded, it makes either end of the secondary winding coils "hot" with voltage, because the two coils are wound in opposite directions from each other.
Because the voltage coming out of the transformer is AC voltage, it is not + and - but we use the symbols to show that the voltage is equal and opposite in polarity.

 

[Gepetto]

SInce he is having a custom made, take these schematics and the original transformer to the custom maker. They are used to dealing with jobs like these and generally speaking have the tools to figure out the number of turns etc. Sometimes by hand unwinding and counting. That is what motor rewinders do very often.

 

[vince666]

Japan is 100V.
Sorry, I forgot your question regarding the dots. The dots are the connector keys. They are marked this way in the schematic to correspond to a feature that keeps them from being inserted backwards. Think of the black dots as "Pin 1".

To better explain, the secondary winding can be a single coil of wire and the voltage would be referenced to zero on one end, for example Yellow = 0V and Yellow = 24V. Or, the secondary could be wound in such a way that there are two coils connected together in the middle, so the coil is "Tapped" at 0V and the two ends have equal and opposite phase voltage on them. for example Yellow = -24V, Yellow with a Red stripe = 0V, and Yellow = +24V. When the middle of the two coils (or Tap) are connected and grounded, it makes either end of the secondary winding coils "hot" with voltage, because the two coils are wound in opposite directions from each other.
Because the voltage coming out of the transformer is AC voltage, it is not + and - but we use the symbols to show that the voltage is equal and opposite in polarity.

to tell you that I fully understand what you are (very kindly) trying to explain me would be an overstatement, of course.

But, at least, I seem to understand that those + and - you mentioned aren't like the + and - we have on DC but they are more a thing related to the phase of AC... and, if so, the order you take the + and - should not have any real importance, true?
I know I should at least try to finally open a book about electrical matters and then another one about electronics and try to read it again and again until I will finally get some of it... I am just missing the basics of such matters.

Anyways, I do thank you again and I am sure my friend knows some more than myself about that... then, hopefully, the informations you shared will be a lot clearer to him (which is what really counts in regards of this Sony deck, after all).

That said, even if I can understand the 5% of what you kindly explained, it will still be useful for me to improve my near-zero knowledge about such stuff.... so, THANK YOU.


@Gepetto: And yes, thanks, will also tell my friend to bring both the schematic and the old transformer to the custom maker... hopefully he will have clearer ideas than my friend... after all, a custom maker of such devices should just know a lot about them and, also, being able to fully understand the schematic at first sight.

 

[J!m]

I would be very concernd about nearly everything after the transformer.

Japan is 100v and it was fed 220v… every voltage after the transformer would be more than double spec; the voltage regulators may or may not survive this. Those have to be tested; plan to replace. Any that test “bad”, the circuit has to be traced further, to see what else may have been damaged.

Check also capacitor voltages compared to double circuit voltage- those would have to be tested; based on cost of a good tester, maybe plan a full recap instead.

you might get lucky but I have a feeling this will not be an inexpensive venture…

 

[vince666]

I would be very concernd about nearly everything after the transformer.

Japan is 100v and it was fed 220v… every voltage after the transformer would be more than double spec; the voltage regulators may or may not survive this. Those have to be tested; plan to replace. Any that test “bad”, the circuit has to be traced further, to see what else may have been damaged.

Check also capacitor voltages compared to double circuit voltage- those would have to be tested; based on cost of a good tester, maybe plan a full recap instead.

you might get lucky but I have a feeling this will not be an inexpensive venture…

at least, the deck itself was totally inexpensive to my friend so if he needs to spend some money to get it working again then it will be well worth, being a truly nice model (surely one of the very best Sony decks ever).

anyways, what you are telling here is quite the same doubt I had just told my friend... in fact, i had assumed that if you double the input voltage then you also get twice the voltage at the output of the secondary.
But my friend replied that, years ago, he was experimenting with a power transformer which wanted 80V at the primary winding and delivered like 12V at the output of the secondary... so he raised the input voltage (i.e. up to 220V) while measuring the output at the secondary and the voltage at the secondary was still at 12V... then he doubts anything got burned after the power transformer and maybe what really got broken is the thermal fuse into the transformer itself...
But being a sealed beast cemented and enclosed into a metal chassis, it cannot be opened and checked inside... that's also why he is directly going to get a new one from a custom builder.
He also just checked the diodes and fuses on the rectifier PCB just after the secondary and they all seem to be OK.
So, maybe, he was lucky and the only true damage is into the transformer... or, at least, we hope so.

And it seems also mlucitt above explained something similar then, of course, we hope he is just right on this as it would also explain why my friend didn't find any burnt fuses on the rectifier PCB just after the secondary windings.

 

[J!m]

I think that scenario depends on the individual transformer.

“in God we trust; everyone else must have lots of data.” A quote from a former boss…

bottom line is you have to prove it’s okay. A new transformer may do nothing, or it may do more damage because down stream components are not doing what they were designed to do now…

 

[vince666]

I think that scenario depends on the individual transformer.

“in God we trust; everyone else must have lots of data.” A quote from a former boss…

bottom line is you have to prove it’s okay. A new transformer may do nothing, or it may do more damage because down stream components are not doing what they were designed to do now…

Of course, as stated above, my near-zero knowledge doesn't allow me to know what's right and what's not about this whole matter.

But, when tomorrow I will translate this whole thread to italian for my friend, I will surely take care of translating your concerns to him as well... which were, after all, also my own concerns.

Nice quote from that former boss!

 

[nakdoc]

To open a thermal fuse in a transformer, current must flow for a considerable amount of time - 10 minutes at least. The problem is all this excess power had to have broken down other parts in the deck. If he is lucky, the broken parts will be the main filter capacitors before the regulators. I believe the most likely damaged part may be the display microprocesor, which typically has -17 volts bias on the filaments. Since that went over -35 voplts, the microprocessor itself could have easily shorted out.
You can attach an AC variac to the top most secondary 28.4 volts ac and then monitor current draw. The other two secondaries will also function but may not have the correct voltages, but there will be enough voltage to check for large ICs that get too hot to touch.

 

[vince666]

To open a thermal fuse in a transformer, current must flow for a considerable amount of time - 10 minutes at least. The problem is all this excess power had to have broken down other parts in the deck. If he is lucky, the broken parts will be the main filter capacitors before the regulators. I believe the most likely damaged part may be the display microprocesor, which typically has -17 volts bias on the filaments. Since that went over -35 voplts, the microprocessor itself could have easily shorted out.
You can attach an AC variac to the top most secondary 28.4 volts ac and then monitor current draw. The other two secondaries will also function but may not have the correct voltages, but there will be enough voltage to check for large ICs that get too hot to touch.

Thanks a lot for further hints, dear nakdoc.
Will translate your message to italian for my friend as well... he will surely find it useful.

And, actually, my friend had also told me that, in his opinion, the guy who damaged this deck had kept it on with 220V for some time, then just enough to open the thermal fuse into the transformer.

If the deck got seriously damaged on other parts, that would be a real shame because that's one of the very best Sony models ever.

Cheers,

Vince.

 

[Skywavebe]

I have to say that the transformer may be the least of his worries and before putting money into this project a Technician might want to use a DC supply first to determine if all else survived this mistake- It is very likely that a new transformer will not make any difference. The single plug in of 220V into a 100 Vac transformer means all the voltages coming out were 2.2 times the amount that would normally be present- I would think in such a case the capacitors rated at 25V getting voltages much higher would short and explode. The rectifiers could open and on and on. The Logic or processors getting higher voltages can also be blown out. There is a lot more testing to see if parts beyond the supply survived the mistake. You need to look at the whole unit as a device as the mistake did not only affect the transformer. Just saying.

 

[vince666]

Thank You, Sam.
Indeed, before putting any good money into this deck, my friend should at least try to check what's still good and what isn't.
Anyways, knowing the right voltages of the secondary is just useful to also know how to feed the deck during some preliminary testing.

Will, of course, translate also your post to my friend, hoping he will put all the needed efforts to try to test the deck before spending money to get a custom built transformer.

Cheers,

Vince.