DC power adapter used insted of a AC power adapter, cause issues?

[doctor]

It will work but it would help to connect the - side of the power adapter to ground so there will be less voltage drop that would increase the current pulled by the boost regulator. It will run on 1.5 volts but efficiency drops a lot. That circuit will supply the bi-polar voltage needed for the analog stages just fine.

Really this device can work with DC power supply.

Due to the fact that after rectifying and filtering 9VAC voltage converts to approximately 12 VDC, the 12 VDC power supply must be used.

Polarity of its output barrel connector does not matter (only for RP-1000).

[Strikerj]

And don't forget to replace U38.

U38 was already replaced, just getting ready to test power before installing the audio processor.

[Strikerj]

It will work but it would help to connect the - side of the power adapter to ground so there will be less voltage drop that would increase the current pulled by the boost regulator. It will run on 1.5 volts but efficiency drops a lot. That circuit will supply the bi-polar voltage needed for the analog stages just fine.

Good tip, dident think of that thank you.

[Enzo]

But if you are going to go to the trouble of requiring the innards, doesn't it seem simpler just to get a proper adaptor? At some point someone will want to power it up and not see your modded adapator, and will then reach for a proper AC adaptor and plug it into the thing that is now no longer ready for it.

[Strikerj]

Thanks for all your advice and tips guys, much appreciated.
This is just a side project so I haven't got lots of time to work on it or the money.
What I have done for now is order another 2 U38's (MP1542) as the replacement IC got hot for a split second when I powered it up for a second.
Testing the power circuit output of U38 and I measured 12 ohms to ground
Seems the original problem is still there.
Ill get a 9AC adapter when I have some extra funds and will continue then Any advice, tips or positive criticisms are welcome

[Enzo]

Next time you remove that IC, measure resistance to the output pin position without the chip. Your 12 ohms could be in the circuit it powers instead of in the IC.

[km6xz]

It is a single chip controller with mosfet switch, it will have 12 ohms or less because it is looking into the high reactance (at those high switching frequencies) of the pulse transformer primary.
There is something else wrong if it was overheating since it has ample current limiting on-chip.

[Mark Hammer]

One day, when world peace has been achieved, and the lion lies down with the lamb, wallwart supplies will come in a sort of see-through clamshell that you can unscrew nondestructively. You'll be able to see what's inside and tell without even having to open it, just how much regulation it is likely to provide, and how easy it might be to either convert to some other output, or achieve the desired regulation.

Some day.... a fella can dream.

[km6xz]

Any switch mode power supply would be a liability nightmare for manufacturers if user accessible. Lawyers collect gigantic jury awards for such invitations to death and destruction every day. No one on this forum who is asking questions about them or trying to fix them have any business messing with them. If they have to ask, they are not anywhere qualified and will absolutely not have the test instruments to repair or modify them without risking their life. They are so cheap, only morbid curiosity drives anyone to attempt to repair a switcher. Sure, a few replace some capacitors in the secondary and feel like heroes based on watching a Youtube video put up by some idiot saying they are simple and they just need a couple caps changed, but odds are better than they will cause more problems than solve and be more dangerous than playing with dynamite. If proper equipped and very familiar with their operation, they can be repaired, but why? If someone is that well equipped and have that much know-how, they are not wasting valuable time on items that cost less to buy new than 10 minutes of their on-the-clock time.

[Strikerj]

Next time you remove that IC, measure resistance to the output pin position without the chip. Your 12 ohms could be in the circuit it powers instead of in the IC.

Thanks, dident mention it before but I did test it after removing U38 it and the short was through the IC but the cause is still unknown.
Im on my lunch break and doing some testing. Good luck me

[Strikerj]

It is a single chip controller with mosfet switch, it will have 12 ohms or less because it is looking into the high reactance (at those high switching frequencies) of the pulse transformer primary.
There is something else wrong if it was overheating since it has ample current limiting on-chip.

Thanks for that, currently trying to trace the fault so Im doing some basic testing at the U38 tabs with the IC removed.

With a multimeter I went over all the pins to ground and here's the results.

OL -1 8- OL
8.4k -2 7- 23M
26M -3 6- 23M
GND -4 5- OL

Then with power on using my oscilloscope.

0v -1 8- 0v
0v -2 7- 7v
7v -3 6- 7v
0v -4 5- -0.4v

Good news is that the 1.8v from U30 is working so Im happy at the moment.

[Strikerj]

Diagnosis continues...

Hi, Im on my lunch break still looking at this thing and found something suspect again.

In the power schematic looking at the output circuit of U38 I found R85, L38 and L37 missing?! (after further inspection found R340 missing but supply to ground?)

It looks like there were no components mounted on the pads (didn't fit the parts?) because it looks like original soldering. Cant be the last bloke that worked on it as his solder work was horrid.

As far as i can see I must fit replacement components to this part of the circuit.

This wouldn't be the cause of U38 getting hot?

Thank you

[g1]

Are you looking at the schematic? L37 & 38 say omit, the resistors say 0 ohms so I would expect jumpers there or elsewhere.

[Strikerj]

Are you looking at the schematic? L37 & 38 say omit, the resistors say 0 ohms so I would expect jumpers there or elsewhere.

R85 is missing and no jumper across tabs.
also no continuity across the pads so I guess ill have to put one in.
L37 & L38 no install as i thought

Thanks

[g1]

So the -15V line is there but the +15 line is not because that resistor is missing?
If someone removed it, then it was likely burnt. If it burnt the unit probably has a fault along the +15V line. You want to correct that before that resistor burns again. Also consider that R85 is acting as a fuse so you must replace it with the same wattage.