Transformer identification

[Ales955]

Hi,

I'm currently trying to repair a STA-602 power amp. I think that the problem comes from the transformer: each time it recceives current, the fuse blows.

My problem is the following: I'm unable to find information on the transformer. It says "model no: jpt-ma600n-2224", OCDE NO: 3084-MA600ND, PROLINE ELECTRIC CORP".
I don't find anything about any of these model numbers or "proline electric corp" on the internet, so I'm a bit stuck.

Any idea welcome !

PS if that hepls, I have the schematic diagram of the amp.

Thanks in advance

Alex

 

[Harald Kapp]

A short circuit in the transformer is possible but not likely. I suggest you first check the output side of the transformer (rectifier(s), filter capacitors (the big electrolytic ones), Ashort circuit on the secondary side has the same effect as a short circuit within the transformer.

The part number and name of the company unfortunately lead me to no or to many results. None of those I checked seem plausible. Sorry.

.

 

[kellys_eye]

Post the schematic.

The most likely cause is either a dud power supply or a short in the output stage(s). As mentioned, the transformer is (possibly) the last source of such problems.

 

[duke37]

Disconnect the rectifier and check the four? diodes for shorts.
Connect a mains light bulb to a blown fuze to limit the current. If the light is dim, the transformer is OK.

Then work towards the output or start at the output by checking the output transistors.

 

[duke37]

Disconnect the rectifier and check the diodes.
Connect a bulb across the blown fuze and see if it lights brightly without a load.

I see it is a stereo amp so you can disconnect each amp and see if the connected one causes the fault

 

[kellys_eye]

Do you have the right rating fuse fitted - this type of amplifier often uses toroidal transformers known for their high in-rush current and need for anti-surge type fuse in the supply line.

 

[Ales955]

Hello,

I completely forgot this thread until I fell back on it right now, still with the same problem. I thank you for your answers.

I've tested the secondary, seems correcy.
I've also tried to unplug de secondary and the fuse broke again, so I really think that there is something with th transformer.
I've tried to unplug the transformer and plug the current, nothing happened (so apparently no problem from the plug/fuse to the main switch)
I've tried the tranformator in resistor mode and I've found nothing alarming (apparently no short circuit in this part)

Still welcoming ideas !

I attached the schematic

 

[Harald Kapp]

R503 in the input circuit is meant to limit the inrush current. Only after C2 has been sufficiently charged via the diodes D501...D504 and the resistors will relay RY501 become active and close the contact across R503 thus reducing power losses in the input circuit and allow the transformer to operate on full mains voltage.
Check the following:

1. R503 should have 10 Ω
2. The relay contact is open when no power is applied.
3. The relay contact closes shortly after power is applied.
4. C502 is open circuit (you'll have to disconnect one leg of the transformer to measure taht.
5. Diodes D501...D504 are o.k.
6. Resistors R501, R501, R505 and R505 are o.k.
7. Coil of Relay RY501 is o.k.

 

[Ales955]

R503 in the input circuit is meant to limit the inrush current. Only after C2 has been sufficiently charged via the diodes D501...D504 and the resistors will relay RY501 become active and close the contact across R503 thus reducing power losses in the input circuit and allow the transformer to operate on full mains voltage.
Check the following:

1. R503 should have 10 Ω
2. The relay contact is open when no power is applied.
3. The relay contact closes shortly after power is applied.
4. C502 is open circuit (you'll have to disconnect one leg of the transformer to measure taht.
5. Diodes D501...D504 are o.k.
6. Resistors R501, R501, R505 and R505 are o.k.
7. Coil of Relay RY501 is o.k.

1 OK
2 OK
3 OK
4 OK
5 OK
6 OK
7 OK

All of this seems ok

 

[Harald Kapp]

A common trick to check the power supply input is to connect a light bulb (not LED) of e.g. 60 W in series with the input. This will limit the current so the internal fuse won't blow. You can then take measurements of voltages and currents to check for unlikely values. Note that the circuit is still connected to mains and all requisite measures have to be taken to prevent the risk of an electric shock.