Whats the test procedure for a DC power supply?

bjornson · 28th August 2003, 01:31 AM

Oh wise ones, please help me with more otari 54c fun..... Every so often a + or - rail will fail. I have to shut down, disconnect the modules, reboot the power supply and then plug modules in one by one and hope for the best. I suspect that one or more of the modules are dragging down the supply rail intermittantly, but there seems to be no pattern to this madness, and fuses rarely blow. The (5) power supplies seem to be delivering proper voltage to the console leg, but i suspect a current issue. How might i use my(scary lookin) phillips 50 mhz dual channel oscilloscope to reveal the truth?

triez · 28th August 2003, 07:28 AM

Try looking about the machine for tantalum capacitors that are going slowly short circuit.

Try putting somewhat downrated fuses in the PSU and running up each module seperately and in groups until one blows to try and find which card is pulling the current.

Run the unit up nice and warm and pull each module in turn and try feeling if any chips are unusually hot.

Look at each rail with your scope and see if any module introduces ripple or sag as you put them in.

Finally, just globally swap out any fixed or variable voltage regulator IC's in the PSU, and the mains filter caps for good measure.

bjornson · 29th August 2003, 02:08 AM

Thanks for your input. Can you define test procedure for identifying ripple and/or sag? I'll report my findings.

triez · 29th August 2003, 01:24 PM

If you look at the supply rails with an appropriate DC coupled setting on your CRO, you should see a smooth straight line offset up or down representing the DC supply. If you plug in a module and the line drops or gets a little wavery maybe that module has a fault. Probably fairly difficult to see though.
Is it the same rail that drops out each time, or the same pair - ie: plus 15 or minus 15? If so you might want to replace the voltage regulators on that rail, particularly if the power supply uses one regulator to derive both voltages.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Power Mac G4 Power Supply Exchange Program	faeflora	Music computers	0	22nd February 2003 07:22 PM
help w/ power supply	Detuned6	So much gear, so little time!	1	30th September 2002 07:22 PM
power supply	C.Lambrechts	High end	2	1st August 2002 02:21 PM

28th August 2003, 01:31 AM	#1
bjornson Lives for gear Join Date: Nov 2002 Location: Pittsburgh Pa Posts: 533	Whats the test procedure for a DC power supply? Oh wise ones, please help me with more otari 54c fun..... Every so often a + or - rail will fail. I have to shut down, disconnect the modules, reboot the power supply and then plug modules in one by one and hope for the best. I suspect that one or more of the modules are dragging down the supply rail intermittantly, but there seems to be no pattern to this madness, and fuses rarely blow. The (5) power supplies seem to be delivering proper voltage to the console leg, but i suspect a current issue. How might i use my(scary lookin) phillips 50 mhz dual channel oscilloscope to reveal the truth?

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search
Display Modes	Rate This Thread
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode	Rate This Thread:

28th August 2003, 07:28 AM	#2
triez Lives for gear Join Date: Apr 2003 Location: Australia Posts: 537	Try looking about the machine for tantalum capacitors that are going slowly short circuit. Try putting somewhat downrated fuses in the PSU and running up each module seperately and in groups until one blows to try and find which card is pulling the current. Run the unit up nice and warm and pull each module in turn and try feeling if any chips are unusually hot. Look at each rail with your scope and see if any module introduces ripple or sag as you put them in. Finally, just globally swap out any fixed or variable voltage regulator IC's in the PSU, and the mains filter caps for good measure.

29th August 2003, 02:08 AM	#3
bjornson Lives for gear Join Date: Nov 2002 Location: Pittsburgh Pa Posts: 533	Thanks for your input. Can you define test procedure for identifying ripple and/or sag? I'll report my findings.

29th August 2003, 01:24 PM	#4
triez Lives for gear Join Date: Apr 2003 Location: Australia Posts: 537	If you look at the supply rails with an appropriate DC coupled setting on your CRO, you should see a smooth straight line offset up or down representing the DC supply. If you plug in a module and the line drops or gets a little wavery maybe that module has a fault. Probably fairly difficult to see though. Is it the same rail that drops out each time, or the same pair - ie: plus 15 or minus 15? If so you might want to replace the voltage regulators on that rail, particularly if the power supply uses one regulator to derive both voltages.