Sony LBT-V302 Compact Hi-Fi Stereo

[ElectroBear]

This system is 20 years old and was working fine until it suffered a serious voltage spike which blew the primary winding of the standby transformer.

The part number is 1-449-723-11 which is NLA (no longer available) - and even the substitute part (9-919-584-58) is NLA.

All information I can find is that is (was?) a 0,5Kva transformer. The blown primary winding is 220v (South Africa), but my problem is to establish the output voltage (to find a replacement).

Complete disassembly and counting the turns would be my last option.

The reason I would like to repair it (as opposed to replacing it), is that it has a matched turntable and I still have a considerable vinyl collection.

Any suggestions (solutions) would be most welcome.

 

[Resqueline]

A 0.5kVA transformer can hardly be called a standby transformer..
A service manual or just a schematic diagram would come in handy. Have you tried to locate one on the net, or is that how/where you got the part numbers from?

 

[(*steve*)]

Yeah, my first question was going to be "what is the output voltage", but I see that is unknown.

Perhaps if you could tell us how many secondary windings there are, the diameter of the wire (wire gauge would be even better), and the DC resistance of each of them.

If you have access to circuit diagrams, that too would be very helpful.

It must have been a massive surge to blow a primary winding of a transformer. I would be concerned with possible further damage. Was it lightning?

Is this the device?

edit: Searching the internet revealed a pdf that tells me HST-V302 is part of the package that is "LBT-V302"

 

[ElectroBear]

Thanks for your prompt replies.

Resqueline
I got the (original) part number from the transformer itself and the replacement part number from a schematic diagram in the Service Manual I found on the net. (The transformer is T902 in the diagram)


Steve
The power surge was massive (± 380v). Some Idiot stole the neutral out of the 3-phase supply at the sub-station which blasted the power supplies to just about every appliance (fridges, aircons, electric fence, burglar alarm, garage door motor, printers, fax, etc) that was running or in standby mode.

We are covered by insurance, but I have already repaired two radios, two printers and I need to repair this Hi-fi because of the turntable.

The radios and printers were all primary winding, MOV, capacitor or fuse failures.

I am assuming that the spike blew the thermal fuse of the transformer.

I have attached the relevant portion of the "Power Board" circuit diagram with the transformer in question highlighted.

I can see it supplies a L78MR06 Voltage Regulator which delivers 6v.

Do I read the schematic correctly that the answer I am looking for is 13.6vac (or thereabouts)?

If so, would the transformer then be a 13.6v - 0v - 13.6v ? (for replacement)

See: Circuit Board

Thank you again for the assistance.

 

[Resqueline]

Ok, it says pin 1 on IC905 receives 13.6V (and so I'd expect RY901 to have a 12V coil).
Doing the math; (13.6V+0.6V)/1.414 = 10V AC. This is from the centertap and to either end - so it's a 20V centertapped transformer. You can get away with an 18V ct.
That's 9-0-9V in other words. Current/power? Find one of (at least) similar size/weight and you'll be ok.

 

[ElectroBear]

Excellent!

Thank you so much for your kind assistance.
Here is a picture of the Power Board (transformer removed)

The relay (RY901) is 12v (see picture)

One more thing... I doubt it is a 0.5kVA as I have seen listed on the net while searching for that Sony part number.

Here are 2 pictures of the transformer with a 5mm LED for size reference.

Would a 1000ma transformer suffice?

Much appreciated!

 

[Resqueline]

Hehe, 0.5kVA = 500VA = 25A @ 20V ~ 500W, no, I don't think so.. Typo?
I doubt the original is even as powerful as 20VA, I guess it's actually more like 5VA (250mA). Look for that first and then confirm the physical size before you buy.
I see the original transformer is also used to support the board, but I guess you can fab something to make it stable if neccessary.

 

[ElectroBear]

...
I see the original transformer is also used to support the board, but I guess you can fab something to make it stable if neccessary.

The board looks to have ample support without using the transformer.

I was thinking if I can find a 9-0-9v 300mA transformer the same size, I could open the transformer casings and swop them. I would then just solder the wires into the board where the pins were... could work...

You guys have really been helpful!

 

[(*steve*)]

It's more likely you'll find a transformer with flying leads.

Connect the leads up and fiigure some way to secure the transformer.

maybe drill a few holes in the board (carefully so as not to cut tracks) then use plastic bolts (so as not to short anything out) to hold the transformer in place.

It may be a good idea to take a lead from earth and connect it to the transformer's housing.

 

[ElectroBear]

I managed to get a 9.5v transformer today (PC board mount)

Only problem, it has 4 output pins. ( See pictures below )

Looking at the circuit diagram, how do I connect the pins to match the required output?

Do I just bridge Pin 2 and Pin 3 for the centre-tap?

Thanks in advance.

 

[(*steve*)]

Do you just bridge pins 2 and 3? Possibly. Either that or 2 and 4 (but 2 and 3 is probably more likely)

Note that you're going to have to find some way of insulating the 220V connection to make this safe. Also note that the equipment will no longer run from 110V after you fit this transformer (because it has no 110V primary winding).

 

[ElectroBear]

Thanks Steve!

The part about insulating and making the 200v safe really makes me laugh!

(Please.... no disrespect to you or your advice intended), but just look at the original power board.... .... that could shock the shite out of you!

I have fitted strip-board to the bottom of the new transformer and I am insulating the soldered side before fitting it. (see below)

The metal transformer casing is screwed (with metal screws) to the back of the metal case of the unit (which is grounded), so I am sure that it is safe. (I am also fitting a plastic spacer)
The Power Board is TOTALLY enclosed once it is assembled, so there is no way a person could get shocked.

I am really grateful for all the advice and assistance you and Resqueline have provided.

Thanks again!

Paul

 

[ElectroBear]

Oops!

Now I'm really confused!

I fitted the transformer and switched the mains power on to the board (power board only) - not connected to the main board yet.

If I test the voltage at the connector that goes to the voltage regulator (7806) on the main board, I get a reading of 33.6v...???

If the transformer is 9-0-9v, where does the 33.6v come from?

In the picture below, the red arrows point to the connector that feeds the main board. (marked 'Gnd', '+' and 'RY')

Testing the voltage between 'Gnd' and '+' reads 33.6v and also between 'Gnd' and 'RY' reads 33.6v. (between '+' and 'RY' = nil)

Please help!

 

[Resqueline]

Good thing you tested it before connecting the electronics..
One explanation I can think of is that the transformer is mislabeled and is really an 18-0-18V.. Check it's AC voltages to be sure.
One other and perhaps more likely explanation is that the center tap wire has somehow swapped position with one of the end wires.
The last miswire would make the full transformer voltage be half-wave rectified and would give those readings you got..

 

[ElectroBear]

DUH!!!... ...How stupid can one person be??... ... (Slaps side of head HARD!)

I was testing it late last night... then I went to bed and lay there thinking carefully... and when I woke up I thought more clearly...

The transformer gives me 10v (centre to either end) and 20v (end to end) ...

The diodes D911 to D914 rectify the current to DCV... so testing the output at the connector, with the multimeter set to ACV, will NOT help!!

With the multimeter set to DCV, I get 15.4vDC.

This looks more like it!

EDIT - UPDATE: All working perfectly! Thank you Steve & Resqueline for your patience and assistance! GREATLY APPRECIATED!

Paul