Power Supply Help Needed

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juniorhifikit

Well-known member
Joined
Jun 14, 2004
Messages
139
Location
California
I have a DDA DMR12 console power supply that needs repair. It's supposed to output +-18volts and 48volts for phantom. It's an interesting circuit in that the regulator is a separate board with discreet components - not a monolithic regulator. Here's the schematic:

http://www.scottgreiner.com/DMR_12_PSU.pdf

Basically, after rectified and filtered there's +-30volts at the emitter of the power transistors, and about the same (from the regulator) on the base. So not much current flow there which equals no voltage output (collector). Obviously there's something wrong with the regulator circuit.

Caps and resistors are fine, so I'm going to swap out all the diodes and transistors on the regulator board. My problem is finding the correct parts. There are so many cross-references, and electronics supplies are a little limited here in Paris. Does anyone recognize these components and know of their common cross-reference names/part numbers?

1N 4148
1N 4002
TIP 31
TIP 32
BC 212
BC182
BC 441
2N 5322

Thanks in advance!
 
First: Why do you want to swap parts? If it ain't broken, don't fix it!

BC212 = pretty normal small signal transistor
BC182 = pretty normal small signal transistor
BC442 = pretty normal small power transistor

Diodes are "normal"

TIP31, 32, a bit slow power transistor but if you want to change this you may be forced to check the frequency properties.

My vote here is that you won't get so much increase in performance just by changing the those parts.

Have you seen my ultra low noise power supplies? I have a couple of them.
http://home.swipnet.se/~w-50719/hifi/jsr06
http://home5.swipnet.se/~w-50674/hifi_pics/hifi_100pr/jsr06r0_overview.jpg
 
[quote author="peranders"]First: Why do you want to swap parts? If it ain't broken, don't fix it!

...[/quote]

Oh, it's broke alright. Like I said, it's supposed to output +-18 volts. But with thelack of current flow from the emitter to the base, there's only about 1.5 volts on the output of the supply. The regulator circuit is bad.
 
What was the cause of the breakdown? High age? Something else?

If high age is the cause, check for dry electrolythics. Check also the TIP-transistors.

How much is bad? All voltages or only one or two?
 
Originally, the problem was voltage too high (+30volts on one rail). Then someone else got in there and messed it all up. Now there's only around 1volt on one rail and around 8volts on the other.

Electrolytics have been replaced as well as the power transistors
 
Oki doki, so now anything may be broken. :sad:

It's a bit sad that the schematic is drawn in a bit unpedagogical way. I'll have to redraw it in order to understand it.
 
[quote author="peranders"]Oki doki, so now anything may be broken. :sad:

It's a bit sad that the schematic is drawn in a bit unpedagogical way. I'll have to redraw it in order to understand it.[/quote]

Indeed. There isn't a whole lot of useful test info included there. I'm reasonably sure that if I shotgun the whole regulator board, the rest of the supply is fine. Problem is, everytime I go to the electronics store, they give me crossed referenced part numbers. Without knowing all of the specs of every supposed part's equivalent, I'm kind of shooting in the dark - which is why I asked about that little parts list I posted. I could just order the EXACT parts online, but I'm in a hurry as recording sessions have been booked by the management (stupid).
 
[quote author="peranders"]If you have replaced any transistors, are you 100% sure you have got the B, E and C right?[/quote]

As far as I can tell...If I could get the EXACT components, I would be sure. That's why I'm posting this - to see if anyone knows the EXACT replacements for these transistors. I'm not finding these EXACT numbers here in Paris and I don't have the cross reference info. I'm having to trust the guy at the counter of the electronics store (not wise) and it's not working.

For instance: is a C556B an EXACT replacement for a BC 212? That's what they gave me...
 
Hi junior hifi,

I just looked up the first 6 parts on your list at mouser.com, and they have them all. Their prices are also probably better than one-off subs at the local shop. So if you're not sure about the replacements being correct, just go to the Mouser website and put the part #s in their search field. They have choices, so you need to choose the right package, etc.

You'll also have to cross-reference pinouts with the datasheet *from the particular manufacturer* of the parts you're using. There's usually a PDF datasheet link at Mouser as well. The datasheets will tell all.

If you're not sure about your current pinouts, you should be able to find datasheets online for the current brand/part you're using, and compare to the datasheets of the originals.

Hope it helps, Paul
 

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