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

[notallbad]

Hi All,
Starting here as I believe the fault to be on the PS but could be wrong, I know it could be a main board issue but hoping the fault lies with the PS and is an easy fix, hopefully!

The PS is in an old organ and on power up nothing happens other than a relay(G6H-2 12VDC) on the main board clicks once, no led display lights up nor does the main board power on red led but this does blink when the organ is powered down.

The PS for this organ gives all the correct output voltages when not connected to the main board, +/- 15v, 5v, 20v(for relay) but when connected to the main board the 5v drops to 1.1v, if I'm measuring that correctly.

The caps look ok and believe it to be glue holding them to the board.

A low power voltage reg, PQ30RV1 reads Pins 1-4 7.68v, 1.1v, 0v, 0.4v.

What could I use as a 5v dummy load, usb fan/mouse? perhaps the amps not rated high enough on the mouse as its only 150mA.

Any further testing/checking?

Help/guidance would be greatly appreciated, thank-you.

[notallbad]

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

OK, so the PS powers the 5V USB LED Fan alright but not really putting it under enough stress to fully test I wouldn't think? Its USB so the fan will be below 0.5A and the reg output is up to 1A.

[Khron]

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

Does that 5v regulator get hot, when powering the mainboard?

[mariushm]

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

First of all, you should make sure it's not a component in the board that's shorted and pulling a lot of current from 5v.
If 5v is overloaded, it's possible to drop to 1.1v or whatever voltage you had.

You can get a digital multimeter, put it in current measurement mode and measure the current drawn when you power the thing and the 5v drops to 1.1v.. then if the current is high you know something eats too much current.

You can disconnect the 5v wire and connect (or solder) 5v from somewhere else (a usb charger for example). If the voltage still drops, you have a short somewhere or something uses too much power.

[notallbad]

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

Hi Thanks.
No it does not, nor do the other 2 regs, 7815 and 7915.

[budm]

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

5 (or 4.7) Ohms for 1A load or 10 Ohms for 1/2 A load.

[notallbad]

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

OK, just to check I did this correctly.

DMM set to 10A, probes connected to DMM in 10ADC and COM jacks, disconnected one of the 5v wires in turn from PS and connected DMM in series.
Also had a second DMM connected to measure voltage.

PS b/d J2 connector
Pin 2 - DMM reading 0.00A, 1.1V
Pin 3 - DMM reading 0.03A, 1.1V

Is this 30mA??

[budm]

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

Yes, 30mA, but that is not right, pin 3 of the IC is the Ground pin. Not sure how you have your setup, the Amp meter should be in series with the load. See the spec sheet of the IC.

[notallbad]

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

Ermm, so still not conclusive? But looking like its main board related.

Sorry budm, please read post above with added info, its Pin2 and 3 on J2 connector of the PS b/d.

[budm]

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

30mA is really nothing, that is very low. Does the Input voltage also drop down, you have indicate 7.68V input with the main board connected. What do you get without the main board connected?

[notallbad]

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

OK, so connected a Nokia mobile phone charger rated output 5V 890mA, actually outputting 6.7v without load.

So now getting LED light up and displaying functions etc...

0.5A
5.6V

Both 5V pins 2 and 3 removed and connected to charger positive and both gnd pins 4 and 5 removed and connected to charger negative.

So looks like it is the PS! Or not? Theres a 'Reset' Pin on J2 outputting 7.8V when either connected as it originally was(when not working) or with the mobile phone charger as the 5V power source (with it working).

Is this a power supply board fault detection signal?

[notallbad]

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

30mA is really nothing, that is very low. Does the Input voltage also drop down, you have indicate 7.68V input with the main board connected. What do you get without the main board connected?

With both connectors removed get 0v on Pin1 of the reg, with just J2 removed get 8v.

This coincidentally is also the 'RESET' Pin1 of J2.

[budm]

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

"With both connectors removed get 0v on Pin1 of the reg" Boy I am really confused, pin1 is an input pin that get the input voltage form the board as shown in the picture, or this input voltage for pin1 is from other board that feeds into the power supply board to supply the input voltage to pin 1 of the regulator. Can I see the bottom side of the board?

[notallbad]

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

Photo of solder side as requested.

Thanks budm appreciate your help.

[budm]

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

OK, pin1 INPUT PIN of the U3 is connected to the positive leg of that largest filter cap of the three on the board through two jumper wires, so it should the voltage even when you remove the connector J2, you can easily trace out that pin 1 connection.
So what is the voltage rating on that large cap, I expect more than 8v on that large filter cap. The so called reset pin is connected to the positive pin of the cap also, please verify. That large cap is fed by the bridge rectifier D4, one of D4 AC pin is fed through a fuse F4.

[notallbad]

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

The cap C10 is a Nichicon 10000uF 16WV, 85 oCentigrade

Also that is all correct as per Service Manual:

[budm]

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

So without J2 in place, check the dc voltage on that cap, this is high current circuit probably for the audio power amplifier section. You had indicated that when J2 is removed, you get 0V on pin 1 of the regulator, post12, that means the big cap is not getting the DC feeding it. F4 is good? You were getting back fed voltage from oustide the board back into the power supply J2.

[notallbad]

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

Aha, I see.

Yes, with the organ only powered by an external 5v it all works except sound output, power up the PS b/d and with the external 5v source you get sound!

But F4 is good, had already checked that and have again to be sure with it out.

[budm]

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

Then what dc do you get on that cap with j2 removed?

[notallbad]

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

With both J1 and J2 disconnected, 8.3v across C10 Cap terminals.

With just J2 connected the cap reads 8v.