| Electronics > Repair |
| HP E3615A power supply slow ramp up |
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| pqass:
R125, C62 aren't suppose to be fitted (see Table A-11 (page A-19)). I think the only other components you didn't touch are R87 and R88. Individually, try shorting their leads together. They're also not necessary* in the case of an ideal comparator configuration. * I'm sure someone will disagree here and will tell you why. But worth a try. |
| gaminn:
Nothing changed. R87 and R88 replaced with new resistors. When R87 is shorted, then voltmeter is chaotically changing values, CV and CC LEDs are on, ammeter shows approx 0.3A. To summarize current state: Nothing connected to rear connectors, all rear switches up. U9C pin 7 is immediatelly steady within 100 uV (measured between U9C pin 7 and OUTPUT+). These parts were removed from PCB: CR22, R19, C36, C29, CR28, CR27, C37. These parts were replaced: U9, R87, R88, R82, R62. Still no change, there is significantly long ramp up when the power supply is turned on (after it was off some time). |
| gaminn:
I'm a little desperate about the slow ramp up, so I tried this: 1) Checked power supply rails for stability - they are stable immediatelly. 2) Tried remote +sense and -sense - nothing 3) I tried to figure out whether the cause of the slow ramp up is electrical or thermal. Normally I have to wait several tens of minutes to again have full length slow ramp up. I tried to forcibly cool down all components on PCB with big fan - this didn't help, the ramp up was not reset. I also tried to discharge all electrolytical capacitors and small yellow (ceramic?) capacitors. Also, this didn't bring full length ramp up without waiting tens of minutes. |
| pqass:
A long shot... Try reflowing the solder pads of U9, R88, R87, R82, R62, C29, S1, S2, S5A. Just to be sure that there isn't a problem with the PCB traces (keeping back switches in up (master, local) position), (a) tacking a temporary wire from R87 directly to +OUTPUT (+front post); purple highlight in my diagram, bypassing S1. (b) tacking a temporary wire from R88 directly to mid-point of R82/R62 divider; pink highlight in my diagram, bypassing S2. (c) tacking a temporary wire from R62 (bottom) to -OUTPUT (-front post); yellow highlight in my diagram, bypassing R9. If the reference is stable (U9C), the comparator (U9B) is working properly, and the CC amp isn't interfering (CC set knob fully CW), then it can only be the sense elements (R82, R62, C29) or their connection to U9B. |
| gaminn:
--- Quote from: pqass on September 07, 2024, 01:26:16 pm ---A long shot... --- End quote --- Thanks again. You can watch this video I recorded: https://youtu.be/Vd9mJ_f1A_Q . The multimeter displays the reference (red U9C.1 and black +OUT). All unnecessary components in CV control circuit disconnected. CC and shutdown circuit also disconnected (R19 and CR22 disconnected). R82, R62, R87, R88 replaced by new resistors. U9 replaced by LF347BN purchased on Mouser. These connections are wired with new temporary wire: U9C.1 - R82 R82 - R62 R82 - R88 R87 - +OUT R62 - -OUT R87 - U9B.6 R88 - U9B.5 Unfortunately still no change... Voltage on main capacitors C8 and C7 is stable immediatelly (16 - 22 V), so is voltage between U9.4 and U9.11 (U9 power supply - approx 28 V). |
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