Keithley 2304A Cannot power on - Page 1
Forum section: electronics / repair

author: anupong1983
author_rank: Contributor
timestamp: March 16, 2018, 04:31:39 am
content: Hello All,Anyone can help me to find out which component need to be replacement?The unit cannot power on, when I pressed the power switch I found the cooling fan is not operate and have some noisy on yellow transformer. I have checked all fuse on board is okay.Hope anyone can help to find out this case, I will so appreciate.Thank you so much.Anupong

author: technogeeky
author_rank: Frequent Contributor
timestamp: March 16, 2018, 11:00:17 pm
content: I have a 2304 and can measure things for you once you get something narrowed down.The power supply is the one part of the device you haven't pictured carefully. You have the output board mostly shown, which is probably fine.

author: bitseeker
author_rank: Super Contributor
timestamp: March 17, 2018, 06:35:54 am
content: Hi, Anupong.It sounds like the problem is likely in the switch mode power supply (the upper-right section in image 20180316_111139.jpg). It's not something that can be determined just by looking at the photos unless a component is obviously burnt or damaged (bulging or popped capacitors). If you don't see any obvious damage, then diagnosis will require taking measurements, some of which must be done with power applied.Since you haven't posted much, I'm not sure what your experience level is. Have you worked on switch mode power supplies (SMPS) before? They generate high voltages (several hundred volts) that could be very hazardous.If you haven't worked with high voltages before, you may want to have someone who has experience with you.Also, make sure your multimeter can safely measure 600VDC or more since your mains voltage appears to be 240VAC. Here, in the US, the mains is only 120VAC, but a switch mode power supply I was working on recently had over 300VDC inside.The first few things that can be checked include the following:SMPS output1. Correct DC voltages measured at output(s). Some power supplies will indicate the nominal voltages on the PCB. Otherwise, post what you see and someone such as technogeeky can compare with a known good unit as to what they should be.If all the outputs are correct, then the SMPS is fine and you can move onto the next board. Otherwise, if one or more voltages are incorrect or missing, the next things to check are on the input side.SMPS input: Warning! High Voltage2. Correct voltage setting for your country (if there is a switch to select it)3. Fuses intact (you said that they were all OK)4. Correct AC voltage measured at the input pins of the rectifier module or diodes (value is usually similar to the mains voltage)5. Correct DC voltage measured at the output pins of the rectifier module or diodes (typicallymains voltage * 1.4)If #4 fails, then verify that there is correct voltage coming out of the input filter module (where the power cord plugs into the rear panel) as it may have gone bad. If the input filter is OK and #4 or #5 fail, the rectifier or diode(s) may be bad. Turn off the power and test them.If all of the above pass, then the first stage of input is OK and the problem lies somewhere in between. The most common failures are with the startup capacitor, startup resistor(s), chopper transistor, feedback opto-isolator (if one is used), or controller IC.Since there are many SMPS designs, it would be helpful to have the schematics for it to see the architecture and components involved. But, this should get you started down the path of isolating what does and doesn't work.

author: anupong1983
author_rank: Contributor
timestamp: March 29, 2018, 04:46:02 am
content: Dear technogeeky,Thank you so much for your reply.Could you help me measure the voltage at the test points that I've marked on the attached picture?I would like to compare with your outcome, thank you so much.--------------------------------------------------Quote from: technogeeky on March 16, 2018, 11:00:17 pm

author: anupong1983
author_rank: Contributor
timestamp: March 29, 2018, 04:50:52 am
content: Dear Bitseeker,Thank you so much for your idea.Quote from: bitseeker on March 17, 2018, 06:35:54 am

author: Phil-Vb
author_rank: Newbie
timestamp: November 18, 2018, 05:49:51 pm
content: Hi AllI would also like to know the voltage as mentioned (asked for) by Anupong. See his picture.I measure 400V but i'm in doubt whether this is what it should be. Anyways that is the voltage going into the Vicor DC convertor. The Vicor module on my unit is not functional, no output voltage. The unit specification says 300Vdc in and 24Vdc out. The unit should be able to handle 400 Vin though according to its specs but that sounds like bad design practice to me using the Vicor unit 100 volts above its nominal input voltage and just at the upper voltage it can handle.Would appreciate some input from the forum before I put the new vigor unit I bought in the K2304 and maybe blow it up.Thank you big time

author: anupong1983
author_rank: Contributor
timestamp: November 20, 2018, 03:17:16 am
content: Hi Phil-Vb,I've measured voltage into the Converter is 405V and no output voltage from the converter.And I already have fixed this faulty unit. I've replaced new VI-263-EU (VICOR) Converter and unit is working property.

author: Phil-Vb
author_rank: Newbie
timestamp: November 20, 2018, 03:48:43 pm
content: Hi AnupongThanks for your reply. I feel confident now to replace the Vicor unit. Got a new one here right beside me but didn’t dare to put it in because I thought the 400V on it’s inputs would perhaps destroy it.Still don’t get it why Keithley feeds 400V into a unit designed for a nominal voltage of 300.Anyway, i’ll try and will post the result.Thanks again

author: jchw4
author_rank: Regular Contributor
timestamp: December 21, 2020, 12:24:39 pm
content: I picked up Keithley 2304A as "For parts or not working".And not surprisingly it does not workI found blown 3A fuse in the power supply, but the replacement one also did not survive for long.So I guess that the VICOR module is dead.But before I replace the module, I am worried that it died.I measured the input to the module, and it's 460V (!). The module is rated to 400V only, so it's not surprising that it died. (My mains are 110V.)They are probably using MAX34262. I guess that schematic follows what datasheethttps://www.onsemi.com/pub/Collateral/MC34262-D.PDFsuggests,with half of sense voltage divider on the top, half on the bottom of the board.I measured 568K from pin1 to V+ and 6.4k from pin1 to GND.The 6.4k seems to match the SMD values of \$6040\ Ohm + 357\ Ohm = 6397\ Ohm \$. I did not desolder R207, which seems to be the other side of the divider, but cosmetically it's in good condition. The value is hidden exactly underneath, unfortunately.If I understood datasheet correctly, the output should be \$2.5V * (\frac {568,000} {6,400} +1) = 224.375V\$ (there is formula on page 10 of the datasheet).Which seems to be exactly twice lower from what I measured!Could somebody with working 2304A measure the input voltage to the module (I labelled the testpoint +400V), and the feedback resistor values (between PIN1 to GND and PIN1 to +400V)?Before I start desoldering random components, is there something obvious that I am missing? Which component is the most suspicious and should be tested first?