Busted RSR HY3005-3 PSU - anybody got a schematic?

[uoficowboy]

Hi - I would like to repair this power supply: http://www.elexp.com/tst_0053.htm

One of the adjustable channels is fairly dead. It seems to give a fairly constant 42V until I load it down with an active load. Voltage and current knobs have very little (but some) effect. The display does still work - it gives the proper voltage and current (though for a while the "." in the voltage display was gone, but it has returned now).

The inside of the device consists of
1x mega transformer
2x transistors hooked to heatsinks (1/adjustable channel(
2x adjustable regulator boards, marked HY007
1x front panel with pots and display board and bananas

I'd love to find a schematic for the HY007 board. I haven't probed around much, but I did notice that one resistor (R39) is sitting at about 120 degrees C. Ouch. R39 on the other board is much happier. Anybody have a schematic for this or a similar device?

Thanks!

[Paul Price]

You might no need a schematic,
It is not so problematic,
Compare the two as though as one,
And some power device you will find,
Reads with a MM something unkind.

A power supply kills its power elements,
First, then other things belie the fault,
But only one weights the way of what is well.
,

[uoficowboy]

You might no need a schematic,
It is not so problematic,
Compare the two as though as one,
And some power device you will find,
Reads with a MM something unkind.

A power supply kills its power elements,
First, then other things belie the fault,
But only one tells the truth of what is well.
,

The power transistors appear to be fine. They're three 2N3055s with the bases and collectors shorted, but separate emitters. Emitters are ORed together with 0.82 5W resistors.

The really hot component (R39) is a 1K that is connected across the big bulk capacitor. When I crank up the other channel to it's maximum voltage the resistor on there gets equally hot. So I don't think that's anything.

I'm comparing the two channels but nothing has stood out yet

[Paul Price]

Bases and Collectors in 3055's should not be shorted,
But married each together in harmony,
Separate, but equal.

[c4757p]

Separate, but equal.

The message, kids, is that you can just swap the two and all will be fine. A base and a collector are actually the same thing.

</troll>

[Paul Price]

What a base thing to say!
According to my rec-collector-shun,

One is an output pin, the other input,
They are not the same, no never the same
save, to a transistor who has felt,
all too much pain!

As for the the board,
You must agree, yea accord,
You cannot call one truth,
while not the other liar!

Perhaps, in the heat of things,
Like in a passion,
In its own wayward way from cool to hotness,
A weld, once worthwhile,
Yet now weary, wastes its promise?

[uoficowboy]

A quick update: I found the problem. I checked the internal supply voltages going to the op-amp and the negative supply had a massive amount of 120 Hz noise. That supply was generated off of a tapped secondary that was rectified and fed into a 330uf 25V capacitor to generate a -24V and a +24V supply. The +24V supply was LDOed to 12V, but the -24V was Zenered to about -15V. Replacing the 330uf capacitor fixed the problem. Looking closely, it has a very small bulge. Barely noticeable, but definitely there.

It's not a super high end supply - but at least it's back to being a functional supply!