HP 6034L broken? - Page 1
Forum section: electronics / repair

author: a111087
author_rank: Contributor
timestamp: October 13, 2014, 07:59:18 pm
content: Ok, I am a total noob.I purchased HP 6034L on eBay because i needed a programmable power supply to test things, but to be honest, I am not sure if this thing even work or I am just dumb.SRQ LED lights up, as well as UNREGULATED LED. Nothing in the back is connected to it. Terminals are clear.Knob for voltage allows to go to 2.46 only. Can't adjust amps.What am I doing wrong?

author: VintageTekFan
author_rank: Regular Contributor
timestamp: October 13, 2014, 09:07:50 pm
content: First, I recommend looking over theservice manual.Those HP power supplies usually have separate sense inputs vs. output - you may need to jumper the S+ and + together, and the S- and - together.

author: a111087
author_rank: Contributor
timestamp: October 13, 2014, 09:13:31 pm
content: yes, i just got the manual, will take a look at it.i also set the jumpers as you said. now i can't adjust anything (stuck at 0.4 volts). same LED's light up

author: VintageTekFan
author_rank: Regular Contributor
timestamp: October 13, 2014, 09:28:03 pm
content: I would verify the OVP setting, see the manual section 3-26.Otherwise, you may have bought a bad supply, and will need to open it up to check it out.

author: a111087
author_rank: Contributor
timestamp: October 13, 2014, 09:52:10 pm
content: OVP is at 65

author: a111087
author_rank: Contributor
timestamp: October 14, 2014, 04:13:35 am
content: well, i read a bit of troubleshooting .... this thing failed all 3 self teststest 1: MODE fault #3test 2: Readback Comparators fault #4test 3: OVP fault #4Manual suggest that problems may be in "power mesh", whatever that is...

author: wn1fju
author_rank: Frequent Contributor
timestamp: October 14, 2014, 12:35:56 pm
content: The "power mesh" is essentially the guts of the power supply - the rest of the circuitry supports the mesh. The mesh operates, as do most switching supplies, by switching a high DC input voltage through (two) transistors (that are pulsed on/off by the controller in a feedback loop) into the primary of a transformer. The energy in the transformer is dumped out the secondary through a flyback diode into a bank of capacitors (that act as a smoothing filter) and then on to the output terminals. Having said this, it takes a considerable amount of expertise (and luck) to fix a switching supply due to the ~300 volts that is lurking around the transistor inputs and the (potentially large) energy that is lurking around the transformer output. You can't, for instance, take a scope probe and hook up the ground lead wherever you want. Ideally, you should be using an isolation transformer with variable output voltage. Anyway, the HP 6034 manual has several troubleshooting trees that allow you to test things with lower voltages. You might want to check the bias supply first. You also might be able to spot things like an open FET or open flyback diode or shorted electrolytic simply by inspection with the thing powered off. Don't forget a thorough visual inspection for burned parts. The HP 6034A that I fixed had a shorted FET (drain-to-gate) that blew up everything along the gate path - lots of burned parts. Good luck!

author: a111087
author_rank: Contributor
timestamp: October 14, 2014, 08:05:33 pm
content: thank you. i will try measuring voltge at the test points as the manual says.i also looked at the boards to see if anything looked burned, but didn't find anything.

author: a111087
author_rank: Contributor
timestamp: October 19, 2014, 07:47:55 am
content: tested control board voltages at points 21 24 and 20 as suggested by the manual. everything looked good.THEN i happened to looked under the fan and saw a huge burn on the board (power mesh board) around two components R6 and R5.Two identical componentsHP part number 0811-1867TQ 2Description: fxd ww 15 k 5% 5 WMfr. Code 28480

author: SeanB
author_rank: Super Contributor
timestamp: October 19, 2014, 08:07:42 am
content: 15k 5W wire wound resistors. Those should have been mounted off the board on ceramic or steel stand offs, so that they were at least their own diameter clear of the board and each other, otherwise they will do like there is on the board and overheat, charring the board and weakening the solder to the point where it has crystallised and gone dry. You probably will have to repair the traces there as it is likely that the traces have lifted at least or cracked through, and the through holes have delaminated. You can reduce the temperature by using 10W resistors if there is space, or by using some wire leads to get to a point where you can mount the new resistors on some terminal tag strips in free air.

author: a111087
author_rank: Contributor
timestamp: October 19, 2014, 08:21:16 am
content: yeah, its right under the huge fan, but fan is NOT blowing on them. so, space there is kinda limited, but i think i can make it work.would you recommend to use this part as a replacement??? (its 6.5W - i'm assuming the higher the wattage, the less heat they will produce??)http://www.digikey.com/product-detail/en/CW00515K00JE73/CWD-15KRCT-ND/1166462

author: SeanB
author_rank: Super Contributor
timestamp: October 19, 2014, 08:25:42 am
content: That will work.

author: a111087
author_rank: Contributor
timestamp: October 19, 2014, 08:27:14 am
content: Quote from: SeanB on October 19, 2014, 08:25:42 amThank you!!! Ordering a replacement... Now I hope that nothing else is broken there.

author: wn1fju
author_rank: Frequent Contributor
timestamp: October 19, 2014, 03:01:01 pm
content: I would sort of doubt that R5/R6 will ultimately be the source of your problems. They are basically (bleeder) resistors in the voltage doubling circuit and unless some traces truly got fried, current should be happily flowing to the FET switchers. Easy enough to verify though. There should be around 300 VDC across the series pair R5/R6. Check it with a floating voltmeter and just to make sure, check it further along the traces that depart the resistor pair, such as C4(+) to C5(-). As you have claimed that you are a novice, be careful! Hook up the test leads with the thing off and then power it on. Keep your hands away since if it is working properly at the voltage doubler, there is enough energy to spoil your day.

author: a111087
author_rank: Contributor
timestamp: October 19, 2014, 11:07:12 pm
content: waiting for my high voltage gloves to arrive before i poke around any more in there.also ordered no touch high voltage sensor, just to be safe... don't want to take any risks over this thing.

author: a111087
author_rank: Contributor
timestamp: October 25, 2014, 05:21:47 pm
content: Well, after actually getting those resistors out and measuring them (they are ok, one was a bit over - 15.17) and then checking all of the traces (which seem to be ok), I also started to think that there there were not the actual problem... I soldered brand new resistors in and issue didn't go away.BUT while removing the Control Board (A2), I saw something that looked like rust on one of the components (not easy to scrape off):One other weird looking component:And finally wanted to know what you guys think of these connectors (from A4 board):

author: wn1fju
author_rank: Frequent Contributor
timestamp: October 25, 2014, 07:14:33 pm
content: I would be surprised if the corrosion on the parts you show in the pictures were the problem. I've seen worse. But the part is a simple op-amp and you can get a rough idea if it is working by verifying that the two input pins are very close in voltage and the output pin should be some nominal value that is not either at the positive or negative rail. At some point, a visual inspection yields no more value and it is time to start checking things following the schematic "left-to-right." Take a look athttp://www.repairfaq.org/sam/smpsfaq.htmand you can get a good idea of the usual culprits (input caps, switching transistors, flyback diode). These are the parts subject to the most stress. Once these are verified, it's time to start looking at the more esoteric support parts, such as control op-amps.

author: a111087
author_rank: Contributor
timestamp: October 25, 2014, 07:17:45 pm
content: thanks, i will see if i can figure out which pins are which on that op-amp.will also continue measuring voltages on A2 board

author: SeanB
author_rank: Super Contributor
timestamp: October 26, 2014, 04:21:48 pm
content: TMS9000 chip just is oxide on the pins. Clean off using a pencil eraser and insert into the socket after a drop of deoxit on the pins and it will work.The opamp in image pin 1 is bottom left, and the silver mica capacitor C22 will be connected most likely to pin 1 and pin 8. Pins 2,3 will be at almost the same voltage WRT pin 4, and pin 6 on the other side is the output.