Electronics > Repair

HP 6177C DC Current Source Repair and Restoration (COMPLETE)

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motocoder:
I added an extra current range to this supply, and I thought I would share the details here in case anyone else wants to do this mod. The standard current ranges on this supply are 500mA, 50mA, and 5mA. These are enabled via current sense resistors of 2, 18, and 180 ohms. The selector switch connects these resistors in series as you go down in range, so you get effective resistances of 2, 20, and 200.

To add an additional, 500uA range, only requires adding a 1.8K resistor and swapping out the 2-pole, 3-position switch for a 2-pole 4-position switch. The switch should be a Make-Before-Break (MBB), also called Shorting, variety as is the OEM part. If a non-shorting variety is used, the supply will generate voltage spikes when the current momentarily drops to zero in-between positions. I had some difficulty sourcing a suitable switch. The closest I could get was a 3-pole, 4-position switch. I just ignored the connections for the 3rd-pole, and this switch worked fine. IT is from Alpha (Taiwan), and is available from Mouser for $2.77:

Alpha Part #: SR2511F-0304-19R0B-E9-S-W
Mouser Part #: 105-SR2511F-34S

For the 1.8K resistor, I chose a 1/2W variety for increased robustness, although this is really not necessary.

The first picture below show a diagram I put together to map out the connections on the OEM switch and how this maps to the new design. Below that I have posted some pictures of the PCB mod and the wiring. I noticed there was an extra, unused hole in the PCB between R2 (the 18ohm sense) and R3 (the 180 ohm sense resistor). I scooted R3 over into this hole so that I could shoehorn in the 1K8 resistor. I had to cut a trace on the bottom of the PCB to do this. Then I connected two wires to the junction of R3 and the new 1.8K resistor, and ran those over to the switch. Use whatever connector you like there so that you can still remove the PCB if needed.




Additional Resistor Shoe-horned in. Not the best soldering job in the world, but it works...


The extra wiring. (Ok, I didn't have a suitable connector)


Extra range. I didn't feel it was worth the effort to re-do the faceplate template.

JuiceKing:
Thanks for the repair tips! I just finished fixing mine, which--like yours--had a bunch of blown zeners and one bad output transistor. I also went ahead and replaced the ugly kludged electrolytics that an earlier repair tech had left behind. I think I paid more in postage for parts (took three tries!) than the darn thing itself. A fun project and a useful instrument. Things got 1000x easier when I bit the bullet and just bought the Artek scanned manual. The legible schematic and grey-scale layout diagram were well worth it!

motocoder:

--- Quote from: JuiceKing on April 01, 2016, 01:03:05 am ---Thanks for the repair tips! I just finished fixing mine, which--like yours--had a bunch of blown zeners and one bad output transistor. I also went ahead and replaced the ugly kludged electrolytics that an earlier repair tech had left behind. I think I paid more in postage for parts (took three tries!) than the darn thing itself. A fun project and a useful instrument. Things got 1000x easier when I bit the bullet and just bought the Artek scanned manual. The legible schematic and grey-scale layout diagram were well worth it!

--- End quote ---

Glad to hear you got it all working. They are really useful. The only thing I would like to change about mine is the negative voltage it briefly outputs when you turn it on. This is a "feature" discussed in the manual. I'd be OK if it was zero volts, but am worried the negative voltage will blow something in the device-under-test.

Ordinaryman1971:
Just got one of those too to be fixed and for completion wanted to post the manuals.
I have two of them. First one is from the HP website, second one is from KO4BB

Ordinaryman1971:
And the Ko4BBB manual for HP6177c

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