Hammond organ PS fault 5v drop - PSH-72A

[notallbad]

Re: Hammond organ PS fault 5v drop - PSH-72A

Theres an A.C Voltage selector 240v, 120v etc..

I am in the UK and it is set to 240v, without power I have changed it back and forth a couple of times just to see if it made a difference, but think I'm only getting 160V A.C.

Looks like I shall have to remove the selector but its more than likely something to do with that massive 'tapping' transformer, I think thats what one would call it!

Gonna have to call it a night for now as she is begging me to bed!!! WooHooooo

Cheers Budm, speak tomorrow hopefully I shall have a couple of pictures and more details regarding the tranny and selector.

[budm]

Re: Hammond organ PS fault 5v drop - PSH-72A

But do you still get 0V at pin 1 when you disconnected the J2:
Post 12 "With both connectors removed get 0v on Pin1 of the reg"
Since you are getting 8v at the cap, then pin1 of the reg should have 8V also, then the output should be 5v with resistor (5 Ohms or 10 Ohms) load connected to the output pin.

[notallbad]

Re: Hammond organ PS fault 5v drop - PSH-72A

With just J1 connected the cap reads 7.98v which is the same as U3 Pin 1.

Sorry, having checked again there does appear to be around 8v on Pin 1 of U3 as there should be with all combinations of J1 and J2 connected/disconnected, not exactly sure what I did there to get 0v, my apologies.

Just to clarify:

There is continuity (0.3 ohms) between Pos leg of Cap C10 and U3 Pin1, J2 Pin1(Reset) and D4 DC '+' Pin.

[budm]

Re: Hammond organ PS fault 5v drop - PSH-72A

"There is continuity (0.3 ohms) between Pos leg of Cap C10 and U3 Pin1, J2 Pin1(Reset) and D4 DC '+' Pin." That is correct, so back to the original problem why the output of the U3 drops down from 5V to 1.10V. You can find out using resistor for the load and see. You may have bad U3.

[notallbad]

Re: Hammond organ PS fault 5v drop - PSH-72A

OK, so how do I do that?

Thanks

[budm]

Re: Hammond organ PS fault 5v drop - PSH-72A

You can leave J2 not connected, then solder in 10 Ohms 5 WATTS (for about 1/2A current draw) between the output pin of U3 and Ground, measure the voltage across the resistor, it should have 5VDC.

[notallbad]

Re: Hammond organ PS fault 5v drop - PSH-72A

So if I remove J2 at the main board end I could place a suitable resistor between Pins 1 and 4 or 5. Correct???

Not sure I have any 5 watt resistors.

[budm]

Re: Hammond organ PS fault 5v drop - PSH-72A

See picture, +5V pin and Grround

[notallbad]

Re: Hammond organ PS fault 5v drop - PSH-72A

Sorry, so it would be J2 Pin 2 or 3 which are the 5v rail and Pin 4 or 5 which is the Gnd rail.

Lucky, I have found a resistor measuring 10 ohms and looking at the size of it I'm guessing its around 5w (though could be 2w) so shall connect and see what voltage measures across it, if it doesn't burn up first.

[notallbad]

Re: Hammond organ PS fault 5v drop - PSH-72A

Connected the resistor with J1 disconnected as well as connected and the voltage across the resistor connected to J2 (with connector removed) Pins 3 and 4 read 1.2v, remove resistor and reads 6v.

Volt Reg U3 Pin1 (Input) reads 7.68v whilst the resistor is connected and rises to 8v when removed.
Volt Reg U3 Pin4 (Adj) reads 0.5v whilst the resistor is connected and rises to 1.4v when removed.

Other than the Output of 1.2v are the other voltages on the reg what are to be expected?

[budm]

Re: Hammond organ PS fault 5v drop - PSH-72A

OK, did any one made the adjustment to the VR1 for setting the output voltage?
By the way, I do suspect that the regulator is bad because the voltage Vref is always 1.25V so the output cannot be lower than the Vref, also the 3.3uf cap on the feedback may have leakage resistance.

[budm]

Re: Hammond organ PS fault 5v drop - PSH-72A

OK, did any one made the adjustment to the VR1 for setting the output voltage?
By the way, I do suspect that the regulator is bad because the voltage Vref is always 1.25V so the output cannot be lower than the Vref, also the 3.3uf cap on the feedback may have leakage resistance.

Also take the resistance reading between input pin and output pin of the regulator.

[notallbad]

Re: Hammond organ PS fault 5v drop - PSH-72A

It is possible that the Vr1 has been adjusted, but not by me, the person I received it from just said that he suspected one of the main board chips needed re-seating but as we all know, never be mislead by sellers/customers. There was no mention that he had tinkered with it.

So the output should never be lower than 1.25v vref, whereas I am getting 1.2v under load.
This I assume would make no difference to any adjustment made by Vr1, output should still be higher than vref regardless.

[notallbad]

Re: Hammond organ PS fault 5v drop - PSH-72A

Would need to remove U3 as getting results as if connecting to a cap, rapidly rising or decreasing resistance

[budm]

Re: Hammond organ PS fault 5v drop - PSH-72A

What I am looking for is the leakage resistance inside the IC between the input pin and the output pin, it looks like the IC is not working. I would replace this IC at this point.

[notallbad]

Re: Hammond organ PS fault 5v drop - PSH-72A

Shall have to find an alternative as don't seem to be able to find one anywhere, closest thing to it is a PQ30RV11 and PQ30RV21 on ebay.

[budm]

Re: Hammond organ PS fault 5v drop - PSH-72A

"PQ30RV11 and PQ30RV21" You can use either of them, they have more precise Vref, 2% instead of 4%, one is 2A instead of 1A. I would like you to adjust that VR1 to see if the out put will change, just mark the location first, you will have to adjust that pot any way when you install the new regulator, make sure to leave the load resistor in place. There is really not much in the circuit at all.

[notallbad]

Re: Hammond organ PS fault 5v drop - PSH-72A

Adjustment of VR1 gives voltage range across J2 Pins 3 (5v) and 4 (gnd) with resistor connected 1.18v to 1.8v.

[notallbad]

Re: Hammond organ PS fault 5v drop - PSH-72A

On the PS b/d I found a leaky cap afterall, shall attach picture, don't know why I did not see it before but it is on the underside. After you mentioned it could be the 3.3uF 50v cap I looked at the 10uF 50v cap too (C13), swapped it out and now get 4.88v on U3 Pin 2 with load.

Hooray, the organ is back up and running!!!

Seriously, thank-you for all your help Budm, it truly is greatly appreciated.

[budm]

Re: Hammond organ PS fault 5v drop - PSH-72A

Great news, hook everything back up and adjust the VR1 for 5V as shown in the service manual.