Not to pile on - I have run the supply outside the case for over an hour. I see no ripple which would alarm me or make me suspect I have a bulk capacitance issue. I too am leaning towards overload trip point. I suppose I will have to figure out some way to load this supply down.?
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On Aug 29, 2022, at 9:41 AM, peter bunge <bunge.pjp@...> wrote:
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Thanks Roger, I can see that many faults can cause the cycling?issue, but mine is an intermittent problem.
It has come and gone over more than a year. It could be a filter capacitor that reforms after being cycled a few times then failing after a long period of not being used. The problem is getting worse but is never there when I want to try something.?
The trip is very marginal and disconnecting the LCD cured it and could be repeated many times. I don't think the problem is in the LCD,? I think it draws just enough current to push past the trip point. That was a year ago and I can't get it to fail permanently now.
I want to take a look at the?+5v filter cap and will try to take it apart today. I was hoping for tips. There is a panel with two screws and soldered wires on the front side of the front half of the supply. I'm hoping I don't have to unsolder them.
It could also be something loading the 5v or it could be the trip point has shifted. The overcurrent does not seem to have a well defined reference. Any power supply overload?would?trip it. One thing at a time.
Peter
On Mon, Aug 29, 2022 at 12:24 AM Roger Henderson <
hendorog@...> wrote:
Late to the party but just in case it helps someone:
My 8753C which uses the same PSU had a cycling fault. It was caused by shorted diodes on the A15 Pre-reg board. CR6 and CR7.
Cheers,
Roger
On Mon, 29 Aug 2022 at 14:22, Ozan <
ozan_g@...> wrote:
On Sun, Aug 28, 2022 at 06:12 PM, peter bunge wrote:
Can someone tell me how the control loop in the pre-regulator controls the 5vD supply? What I see is T1 connected to line at E1 and E2 and switching FETs that don't seem to control anything and only drive RT1 and RT2.Is there a winding in the loop that acts like a MagAmp? The common connection of the?FETs connects through capacitor?C8 to A15A1 transformer,?what and where is that? .
What am I missing? The manual is very vague simply stating "The?+5D supply is regulated by the control loop in A15"
Am I missing a schematic? I have one for 08753-60215 and one for 08753-60115. there is a T1 on each board which makes it more confusing.
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Hi Peter,
I briefly looked at the schematic of 8753A.
Hopefully 8753E is similar. Mains input is rectified on C3 and C4, RT1 and RT2 are inrush current limiting NTCs. Q1 and Q2 turn on alternatively, creating an AC waveform that flows through C6 (probably C8 in your schematic) and primary of "Power Transformer". Return path of the primary is through "T3 Over Current Detection" transformer and back to mains input through S2 switch (which selects 110/220 tap points). 8753A schematic and board layout show the power transformer on A15 board.?
Ozan
