Sir partyanimallighting
Au Contraire . . . .
Looks like you
DEFINITELY reversed some of your parts identifications.
Specifically . . . .
The top
YG901C2 dual diode with common anode is a 5A fast switching unit which creates your lower voltage supply with the storage of its two 25VDC max electrolytics nearby . It looks to
NOT be heatsinked.
The lower
YG901C2 dual diode companion . . .which is heat sink clamped . . . creates the higher voltage supply with its the three - 35VDC max E caps.
That supply is being referenced to send back any load variance / voltage pull down back to the
4 pin POWER " switch mode power supply in a chip"
Where, if it detects a voltage pull down, it sends a wider pulse width square wave to the power transformer primary for corresponding compensation.
Your mismarking is being in the
ALSO assigning of the
YG901C2 parts designation to the
4 pin POWER " switch mode power supply in a chip" .
Your "wheezing" power supply condition is telling us that the basic RAW DC high voltage supply and its pigtail fuse is good and HV dc is present at the LARGE HV electrolytic at mid chassis.
Each of the
YG901C2 full wave rectifiers dump into an initial E-cap and then a series ferrite cored choke ( black heat shrink wrapped) and some more E-caps , on past, for final filtering.
With time and use and
ALL of the high frequency hammering *** that those initial E-caps receive, from the strong squarewave waveforms coming into them, will start declining in filtering effectiveness and the developing of an ever increasing ESR, overheating and a consequential electrolyte pressure seepage.With a last gasp, final drying out.
There is being such a decline in performance, such that they can no longer keep up with the needs of the power requirements. Thus the surging, while it is TRYING to fulfill a keep up level.
***
https://cdn.dribbble.com/users/1181466/screenshots/3592598/02_construction_.gif
If you are having almost zero techno measurement apabilities of analytical ripple and waveform situations, minimally, you could take a full leaded length ~ 1000 ufd at 35VDC new / known good E-cap and shunt across the first cap of the lower power supply and fire up to see if the surging abates to a disappearing or slowing down a bit of the surging.
Then pull it and move thru all of the other cluster of E-caps in that area . . . one at a time.
PLUS there is one more E-cap being involved, and that is a value that I can not read, it is being black and physically located at the 11:00 clock position from your
YELLOW marked up heated resistor .
( And that resistor probably will be inserted series wise, within the HOT ground return of the units
4 pin " SMPS in a chip"
You do not need to pull existing E-caps . . . just solder tack your substitute E-cap in parallel across them.
TRIPLE CHECKING POLARITY MATCH.
ALSO . . . .if the power supply has run for 5-10 minutes . . . marginal / bad caps tend to start warming up, so compare temperature between caps with a fingertip.
Au Fin . . .
Sometimes you will (/
CAN)
see (
LASER ETCHED )
numbers on a "cooked" device by shining a (
VERY BRIGHT )
light on it at an (
SPECIFIC)
angle.
. . . .(
with the viewing help of a magnifier)
True . . . true . . .VERY TRUE !
Thaaaaaaassssssit . . . . .
73's de Edd . . . . .
A boiled egg is . . . is . . . is . . . . hard to beat.
.