Data East power supply problem

[Dimsims]

Hi all,
I have a Data East power supply (520-5047-00) thats playing up 
The R15 resistor is as hot as hell (finger sizzling lol) & the dmd screen isn't working as a result of the power supply.
I tried the dmd in another machine and it works.

I've replaced allot of parts in the HV section but still no good.

Any ideas ?

[Homepin]

Ideas? Yes.....get a multimeter and start measuring voltages. You cannot "guess" a problem like this and simply shotgunning parts is not a fast, easy or sensible way to find the fault.

These are very simple, regulated supplies so a measurement of all the voltages should reveal exactly what area your fault is in which will narrow it down to a few components.

[Dimsims]

Ideas? Yes.....get a multimeter and start measuring voltages. You cannot "guess" a problem like this and simply shotgunning parts is not a fast, easy or sensible way to find the fault.

These are very simple, regulated supplies so a measurement of all the voltages should reveal exactly what area your fault is in which will narrow it down to a few components.

OH yes I forgot to say I tested the voltages 

All is good bar the 68v, is only reading 22v.

[Steevsee]

Did you already replace D9, 68 volt zener?

[Steevsee]

Check connector CN1 on power supply.  Make sure no burnt pins or cold joints.

Test for 68 volts DC at Diode D5, banded side positive, negative to ground.

If no/low volts, test/replace the following components in order.
Resistors
R8 - 47K, R11 - 330K, R12 - 1.5K and R15 -500R.

Diodes
D5 - IN4004, D6 - IN5228(3.9v zener) and D9 - IN4760(68v zener)

Transistors
TR1 - MPSA92 and TR3 - MJE340

Also capacitor C10 is important for 68 volts.

The above components comprise the entire 68 volt section of the power supply board.

[Dimsims]

Thanks heaps for the info Steevsee 

Ok, so I've tested the D5 diode, it was working but I replaced it anyway and tested for 68 volts and got 140 volts 
At the CN5 68 volt pin, its reading 25 volts

R11 - 330k tested to 356k, so that was replaced.
Also R8 & R12 tested ok.

I've replaced: D6 - 1n5228, D9 - 1n4760, TR1 - MPSA92 and TR3 - MJE340

Im waited for caps to arrive for C10 & C11

68 volt test was done after parts were replaced.

Could it be the C10 cap ?

[Dimsims]

Desoldered the C10 & C10 caps, tested them and both caps test "OL" (over limit)
Not sure if my multimeter is playing funny buggers ?

Hopefully I get the new ones tomorrow 

[Steevsee]

My bad on the diode voltage reading.
The input volts is 100vdc at the diode and without a load, your reading is probably OK.

Hopefully C10 will improve your output volts.

C11 is part of the negative volts DC circuit, but won't hurt to replace it as well.

[Dimsims]

The caps for C10 & C11 showed up today, I soldered them in but still no go 

Not sure where to look now ?

[Steevsee]

So you're still only measuring around 20 volts output?

[Dimsims]

Yup, 23v

[Steevsee]

Just checked circuit again.
Looks like C13 filters the final stage voltage in this circuit.
Seems to be the only other possible candidate.

Edit.
Just realized my JP has the same 68 volt circuit as your board.
Tomorrow I will measure my voltages at various points along the circuit.
This may hopefully help narrow down the problem.

[Dimsims]

Just checked circuit again.
Looks like C13 filters the final stage voltage in this circuit.
Seems to be the only other possible candidate.

Edit.
Just realized my JP has the same 68 volt circuit as your board.
Tomorrow I will measure my voltages at various points along the circuit.
This may hopefully help narrow down the problem.

Thank would be great 

I did replace C12 & C13 already, so yeah I'm not sure.
As I said in my first post, the R15 resistor is getting super hot, enough to melt the solder.

[Steevsee]

Ill check my R15 Tomorrow as well.

[Dimsims]

Here is a picture of it before I started replacing parts: