HP 740B DC Standard Ultimate Restoration

[Hewlett Me Out]

Currently:



But you need the backstory:



Fresh out of the asylum with big ideas and money to burn on a Vishay metal foil addiction, I set out to calibrate my HP 3440A with whatever I could get my hands on first, dead or alive. That just happened to be a 740B with of course the 419A along with a 735A to calibrate the 740B. Now I'm not well or one to leave well enough alone and I don't subscribe to the "if it ain't broke" mentality in my mental state so it was sensible to completely rebuild this DC Standard and when the manual told me the oven wasn't serviceable, I took that personally and serviced it anyway. HP lied to you.







With my oven fully Vishayed and the zener installed (not pictured), I was confident that the oven would be sufficient for my four digit needs.

Then I thought to myself, how can my oven reach its full potential if my power supply and regulator for the oven & reference weren't fully Vishayed too?

To be continued...

[Vgkid]

Looking forward to the updates.

[Hewlett Me Out]

Before this thread is filled up with a lot of information that likely won't be needed for normal operation, here are a few tips that I think take some complex topics and simplifies them:
-the heater/reference board is repairable, just do not try to use a dual NPN on the heater side of the board. It will not work properly. Additionally, if you take the board out, you should cut all of the wires close to the board and strip new leads. Good chance your wires are oxidized. That includes the ones for the thermistor. The white substance is just silicone sealant and easily detaches from the board. Apply new silicone in the same way when you reinstall the board. Mind your component heights and make sure you're not shorting anything with the interior of the oven.
-while there is another thread on this DC Standard, the information seems to complicate a relatively simple repair process. Contrary to what that thread indicates, there are neons available for the choppers and they do work. I grabbed two C2As at random from a bag of 20 I had just yesterday and put them in the main loop. While the process for accessing the board holding the neon bulbs was a pain, this repair does not need to include an LED retrofit. This information would also apply to the 419A. Certainly possible you could get better results if you went through an aging and matching process on your neon bulbs, but it does not seem necessary when there are other probably more meaningful performance improvements to be had elsewhere...