| Products > Test Equipment |
| My poor mans SMU - The Agilent 66311B |
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| TheSteve:
Looks like I have an 66319D coming. It has dual outputs and the volt meter option. It can also do battery emulation. Should be fun to compare it to the 66311B to see what the differences are. I will also post the firmware. |
| ve7xen:
So a lesson in getting too overzealous with repairs... Today I decided to poke around the front panel board and try and get a bit more brightness out of my VFD by running the filaments hot for a few minutes. While probing around looking for the filament supply, I accidentally shorted the last two pins in one of the groups on the VFD - something at +12V and a driver output or micro pin or something. Killed the whole front panel, just junk on the display. Of course I couldn't put it down and think clearly or be patient, so i attempted to use a heat gun to desolder the VFD and inspect the circuits on the other side, with the intent of replacing whatever part I'd fed 12V up the backside of. Of course the heat gun is not the correct tool for the job, and I now have a ruined FFC connector and several random parts unintentionally desoldered - but the VFD remains. If anyone has a picture of the top side of the front panel PCB, without the VFD installed, or a schematic, or even a BOM with part designators, that would be extremely helpful. I don't think there is component level information available on this box, but maybe there are other models using the same front panel? Also knowing what 8-pin FFC connector would work would be nice, though there is an unused one on the mainboard I can steal. |
| stuartk:
I know how you feel. A few days ago I trashed a $60 TFT touch panel and a 100 pin Pic32MX while probing voltages not realizing that my multi meter probes were in the current slot instead of a voltage slot. :palm: Desoldering the pic and 5 blown SMD IC's was a real joy I think it's worthwhile to fire off an email to the guy on ebay we bought these units from. For all we know he might have some junk units too bad to sell that may have parts. He seems to have acquired dozens of them anyways. You should post a pic of the damage. |
| ve7xen:
And the sad story continues... After painstakingly removing the VFD properly, I began the process of determining where the parts that fell off might live, there are no silkscreens, and which parts were likely damaged and would need to be replaced. The board consists primarily of an Intel TN87C196 16-bit microprocessor (OTP) and two Allegro UCN5812 VFD drivers. There is also a MAX773 DC-DC converter (to generate the 12V rail), and some other miscellaneous components. I decided to power up the front-panel board from a bench PSU and try to determine which part was bad. This was easy enough, it's just a 5V rail. At 1A, the supply was still in CC mode at about 2V so I figure there must be a short. Not finding anything obviously getting hot other than the DC-DC converter, which made me suspect one of the 5812s (which I would have guessed anyway), I decided to proceed with resoldering the components that fell off. The ICL7660 was one of the desoldered parts, and studying its pinout it was pretty easy to determine which space it went in due to the boost capacitor's placement. It was replaced. As I did not want to fully reverse engineer the circuit, I thought I would power the board up again to measure around the pads for the dual FET and determine its orientation. In the process of doing so, Mr Bozo struck again, and I reversed the power supply to the board. Unlike many of HP's well engineered products, the board has no reverse power protection, not that it would normally need it. Getting that dreaded feeling, I went to steal the "spare" FFC connector on the main board to connect it back up. I had previously noticed that the main fan doesn't start for 15s or so when the front panel is disconnected, so I could test the board that way. I now suspect the main controller has been killed too, as when it's connected to the main board, I get the same delayed startup that happens when the front panel was disconnected, so it seems that the main board can't communicate with it anymore (this was, I think, still working after my initial blunder). So I'm left in a difficult position on repairing this. I might be able to get a new TN87C196, there seem to be some on eBay that are claimed to be new, however getting the code is likely impossible. I think it's nearly certain that it's dead, so my options are more or less to find a replacement front-panel board from a donor unit, or reassemble it and sell it on as for parts. I don't think it's worth ordering the likely parts I killed the first time around at this point, unless someone can give a story where a 1990s microcontroller survived a reverse voltage for 30s. I'm still going to try repairing the front panel board as best I can to take some high-res photos for anyone else that may come across having to repair one in the future. Stay tuned. |
| ve7xen:
So I might have actually been saved on this one...the main power supply to the MCU runs through one of the passives that fell off the board and I hadn't reinstalled yet. I realized that I couldn't have tested the front panel board that way after my initial blunder, since the FFC connector was fried. After replacing the passives in the correct spots and powering up through the main unit, I don't get the long fan start delay any longer, it's a more typical 2-3s. The box still doesn't respond on RS232, which is a bit odd to me, but progress! After powering up that way, I found the lower-left 5812 gets hot, and it was the part I suspected based on what I'd shorted anyway, so a definite direction now. I will order all the candidate ICs - I think they are all pretty easily obtainable and proceed with a repair attempt. The reverse voltage might have fried one of the other bits, but they're cheap and easy to replace compared to the MCU. Attached is an annotated photo of the board for anyone who comes across this thread in the future. I've posted the full resolution of that image, plus some other photos, at http://www.gotroot.ca/66311b . A blog post will probably come eventually, if I get this thing working again. |
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