| Electronics > Repair |
| HP E3615A power supply slow ramp up |
| (1/7) > >> |
| gaminn:
Hi, recently I noticed that when I turn on my E3615A set e.g. for 5V, it takes it some time to reach 5V. Immediatelly after power the voltage is 4.30 V and after approx 1 minute it reaches 4.98V. After several minutes it finally gets to 5V. No load connected to the power supply. What can be wrong with it? |
| MathWizard:
What's it like at other voltages, are there are relays that click on for voltage ranges? It sounds like something warms up and drifts back to good. Have you tried it with a load, and see what happens when stuff starts to heat up quicker ? I wonder what the PSU section is doing, maybe some rail is slow to regulate, like some transistor that's slow turning on or whatever. I don't see the E3615 schematic, here's the E3610-3613 manuals, I hope they are similar, there's not much to them really. https://xdevs.com/doc/HP_Agilent_Keysight/HP%20E3610A,%2011A,%2012A%20Operating%20&%20Service.pdf |
| pqass:
Service manual is here. Schematics on PDF page 34. The CV and CC amplifier blocks are more complex than the E3610-12A supplies. On first power up (after hours of being off) is the CV LED on or does it start with the CC LED on first (or both LEDs on)? Is the OVP LED on at any time? Try turning the current knob fully clockwise and try restarting (with no load attached). Does the same slow ramp up occur even after the unit is warmed-up? ie. After being on for an hour, turning the unit off for 10 seconds then on again. |
| gaminn:
Thanks guys. 1) CC LED is not on during the slow ramp up. 2) After 90 minutes of being powered off, without load, the unit reaches 4.95 V after approx 30 seconds. With 5 ohm load, it is seems to be the same amount of time. 3) When the unit is warmed up, i.e. 1 hour on, 10 seconds off then on, it reaches set voltage immediatelly. |
| pqass:
First,lets confirm that the built-in voltmeter isn't the culprit here. Connect an external trusted multimeter/bench meter (in VDC mode) to the PS output and try powering again from a cold PS (many hours off). If the attached multimeter exhibits the same slow ramp-up then it confirms that something in the PS voltage feedback loop is the culprit. Proceed to the next test below. Secondly, attach a trusted multimeter/bench meter (capable of 1 millivolt resolution@10V, ie. 4-1/2 digits or 20,000 count; in VDC mode) between TP6 (black) and TP7(red). Again, after a cold start, confirm that the reading is a steady +10V (or close to it). Confirm that this reading DOES NOT ramp-up/down (should be stable just seconds after power-up). If the TP7/TP6 reading experiences a similar ramp-up/down over 30 seconds (or whatever until stable at a similar rate to the built-in voltmeter), then that points to U15 (LM336BZ-5.0); the voltage reference. Confirm again, this time TP6(black) and R109 (red on opposite of the -12V resistor lead). It should be -5V (or close to it). If you see the same ramp-up/down (opposite polarity and half the magnitude of previous TP7 reading, over the 30 seconds 'till stable) then it's definitely U15. |
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