HP 8563E Power Issues - Page 1
Forum section: electronics / repair

author: jonsikul
author_rank: Contributor
timestamp: June 25, 2024, 02:40:24 pm
content: I recently got my hands on an 8563E. It turned on when I got it and display was pretty good and it was able to measure quite nicely.The only thing was the keypad didn't work on some of the buttons so I opened it up and cleaned it.I figured while I had it open I would recap the power supply, so I got new electrolytics comparable to the older ones.I felt pretty happy to get that out of the way and hopefully prevent some power supply damage in the future.So I recapped all electrolytics and put it back, and now when I turn on, the +5V and the +15V surprisingly don't come up (5V is stuck at 3V and 15 at 10V). It seems as though the A14 and A15 are keeping them down as if they got damaged by my tinkering. It seems to me that the overcurrent protection is the reason for the low voltages.I tried a electronic load on both +5V and +15V supplies and they could handle quite some load (a few amps) without going down.When I disconnect both of them from power, the supplies come up and no problem. But with them connected I measure 2.3Ohm (short) on the 5V and 55Ohm on the 15V. Now, there are quite a lot of components on A14 and A15 that use 5V and 15V so it would be a nightmare to try to desolder each component and put it back again. I have looked at the most obvious tantal caps at the input of those boards but no dice.I believe I was rather careful when handling the electronics in regards to ESD etc.Any experience with a similar issue or any advice other than desolder everything?

author: Harry_22
author_rank: Frequent Contributor
timestamp: June 26, 2024, 02:02:53 pm
content: Hi!Could you post photos to make it clearer what this PSU is like?

author: jonsikul
author_rank: Contributor
timestamp: July 18, 2024, 09:20:22 pm
content: I "fixed" the previous problem by putting the original capacitors back. The supply apparently didn't like the new low ESR capacitors.I am however stuck at another problem. The CRT only turns on when the system has been turned off for a while (30min+, sometimes more) The CRT power supply schematic shown in the picture below. If I turn off the device and wait a couple of minutes and turn on again, the CRT does not turn on.3 schematics are shown.1. CRT power supply with switch mode supply2. CRT driver with x-, y- deflection amplifiers etc.3. HV transformer/multiplierAs I understand the functionality of this power supply (and feel free to correct me) the CRT power supply is a switch mode supply and connected to the primary winding of the HV transformer/multiplier (also schematic below, a bit blurry). 110V is generated on a secondary winding. This 110V is used as feedback for the CRT power supply. The 110V is also used to power some x-deflection amplifiers and more on the CRT driver board (see schematic below). 2.45kV are generated for the cathode supply and CRT heater as mentioned before. 9kV is also generated for the post accelerator.Now if I disconnect the 3x 2.45kV that is generated in the HV transformer/multiplier from the CRT driver board and by extension the CRT heater and cathode, the 110V come up nicely and are stable. If I don't, then the switch mode supply tries endlessly to start but without luck. When "cold" the 110V come up, but after like 2+ seconds of the switch mode supply trying to come up and then finally are able to.When I am successful in turning the CRT on, it looks quite nice, i.e. no focus problems nor intensity problems.From what I understand when a HV transformer/multiplier fails, it fails totally and completely which is why I have kind of ruled that one out. Remaining are either the CRT itself, or the CRT driver.Any advice on how to figure out which it is, would be most helpful.