Re: HP-8753E Power Cycles at Start Up
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I took the cover off and everything works. I have no idea what the problem was. This unit had a manufacturer's fault on it for 30+ years. The problem showed up once and fixed itself after re-seating?boards but I could not confirm what fixed it. Two years later the fault re-appeared and it was these two bad solder joints. It is not the problem this time because they were re-soldered and the symptoms are different anyway. So the fan was surging and it would not start up. I will 'scope the filter caps before putting the cover back on. How are you making out with yours?
My HP8753B suddenly started doing this surging with all the front lights on (I will have to re-check that statement but it is what I remember). This was several weeks ago and I have not had time to check it. If you start on yours take the top lid off and look at the row of lights on the power supply board. They should be green if OK and red to indicate a bad power supply (I'm going from memory so anyone correct me if I am wrong). Check the?power supplies with a good digital meter BUT DO NOT ADJUST ANY, especially if they are marginally off,?you do not want an additional fault of your own doing. Check each one with a 'scope and I would not be surprised if you find high ripple on one or more in which case replace the bad capacitor.? The manual will tell you what they should look like. Also there is?a start up sequence for the?CPU row of red lights. Check the manual. The fans are special on these?and are?controlled by a circuit. The VNA will not turn on if the?fan is bad and it?must be replaced by the correct one. I will be starting on mine next week, possibly Monday. I have family visiting right now. Peter.
On Fri, Aug 26, 2022 at 7:35 PM Rich Miller via <av8torrich= [email protected]> wrote: All:
My HP-8753E started demonstrating what I believe is a PSU related fault. When I switch the VNA on, it attempts to boot up, but before it can, I hear the fan stop, and then turn back on, and the VNA attempts a start again. This cycle goes on forever at this point.
I have taken a close look at the spare PSU, and there are no fuses externally. I also note there is a Voltage Regulator Board. I am wondering if anyone has had this issue, and was it the PSU itself or the Regulator Board?
My thinking is if this was a hard fault in the PSU something would have self destructed, or blown a component/fuse internal to the PSU. That being said, I have never seen the inside of the PSU to know if there is some sort of soft restart, or a fuse which should blow.
I would also be curious if there is some other protection feature in the 8753E which would cause it to power cycle like I describe above?
Thanks in advance!
Rich
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