# HG changeset patch # User David Douard # Date 1523480967 -7200 # Node ID 6233ca28a05cd984770ccb284210f29d886192b5 # Parent ce8a1de2722634b178d9ddd557236061d8d65eee [hp8662a] minor improvements diff -r ce8a1de27226 -r 6233ca28a05c content/hp8662a.rst --- a/content/hp8662a.rst Sat Mar 24 01:43:02 2018 +0100 +++ b/content/hp8662a.rst Wed Apr 11 23:09:27 2018 +0200 @@ -111,12 +111,13 @@ the culprit for the smoke: the input protection thermistor. Strangely, it still measures a decent resistance value, but hey. -The thermisor is descrived the old fashion way: it's a 5ohm@25°C with a +The thermistor is described the old fashion way: it's a 5Ω @25°C with a temperature coefficient of -3.8%/°C. I did not find an exact replacement in my junk parts; only a slighty highter value one (a XXX, which is more like -20ohms@25°C). Not ideal, but for now, it seems to work fine. +20Ω @25°C). Not ideal, but for now, it seems to work fine. .. image:: {filename}images/hp8662a/smoking_thermistor.jpg + :class: image-process-large-photo After this first step forward, I was not confident enought to plug the boards back in place and try again (I am always worried when I repair switching @@ -136,6 +137,8 @@ did not stay on, and the error LED did turn on. All the voltages produced by the inverter board were very low. Somethin was wrong. +.. image:: {filename}images/hp8662a/PSU_inverter_schematic.jpeg + Looking at the schematics and the boards, I did find several failure points: - one of the 2 150µH inductors on the 160VDC rails (L6 anf L7 on A7A3) ) looked @@ -151,21 +154,21 @@ the 2 switching (bipolar!) transistors (first time I see the base of an NPN transistor protected by a fuse, but it's also the first time I repair a switching PSU which the main switching transistors are bipolar ones and not - MOSFET or so). These are small XXX fuses, they look nice and so but are very - expensive (and a bit hard to find): something like 15€ each. So for now, I've - replaced it with a simple 5x20 glass fuse: not as pretty but does the job for - a few cents. + MOSFET or so). These are small BUSS GMW 4/10 (400mA) fuses, they look nice + and so but are very expensive (and a bit hard to find): something like 15€ + each. So for now, I've replaced it with a simple 5x20 glass fuse: not as + skookum but does the job for a few cents. .. image:: {filename}images/hp8662a/broken_choke.jpg After these fixes, I reassembled the PSU and tried again: the result was quite promising, but not a complete success: the PSU seemed to start, but very quickly stops itself with an error LED on: the overvoltage protection was -activated. +shuting down the power. I tried to check several things on the error detection circuits with no succes, -and followed the service manual instruction, until I found this in the service -manual, about this overvoltage error: +and when (at last) I began to follow the service manual instructions, I found +this paragraph about this overvoltage error: If red LED in the upper left hand corner of the board is lit indicating the input voltagr from the A7A3 Inverter assembly was too high and the supply was diff -r ce8a1de27226 -r 6233ca28a05c content/images/hp8662a/dirty_hp.jpg Binary file content/images/hp8662a/dirty_hp.jpg has changed diff -r ce8a1de27226 -r 6233ca28a05c content/images/hp8662a/reassembling_1.jpg Binary file content/images/hp8662a/reassembling_1.jpg has changed diff -r ce8a1de27226 -r 6233ca28a05c content/images/hp8662a/reassembling_2.jpg Binary file content/images/hp8662a/reassembling_2.jpg has changed