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HP E3640A Teardown

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On air now ...

This one's the E3640 which is essential an E3410 but in a modernized , spiffied up version with GPIB and all bells and whistles.

The machine sports the classical HP/Agilent front style with rubber membrane keypad and a VFD starburst (14 segment ) display.

The backside has the fan opening, GPIB and RS232 connections and additional output terminals as well as sense wires.

The machine is built on a single multilayer PCB and has big fat traces to conduct the current everywhere.

The brains of the machine are formed around the classical 80C196 and the custom asic that is common in a lot of machines of this lineage. they use the multislope III convertor for all measurements. A simple ram and rom complete the digital portion. commnication to the frontpanel is over a serial link and the frontpanel has its own 87c51 that does keypad and display scanning.

As in any decent test equipment everything is galvanically isolated and an outguard , earth referenced, section handles all I/O. an otpical bridge connects outguard and inguard.

the outguard has a 87c51 and a mp9914 to hande RS232 and GPIb operations.

The power section uses active switching useing mosfets and a recitfier. The transformer has multiple taps and the supply switches in function of the selected output voltage to reduce power dissipation.

Even though the machine can not make more than 20 volts or 3 ampere the main tank capacitor is impressive 10000uf 50 volts. Clearly no underdimensioned ,penny pinching flimsy cheapo caps here ... let's put a whopper in there. This thing has to last a while ...

An odditiy :

A regulator chip from Cherry. Yes , those guys famous for the keyboards ... They did dabble in semiconductors for a while but sold lot stock and barrel in 2000 to On semiconductor.

And finally a pancake transformer.

This makes all thevoltage required for the system , and there's quite a lot. filament for the vfd , 4 or 5 for the control electronics , mulitple primaries for the 110/220 and mulitple power secondaries.

I got this one in the same skip as the 34970 i mentioned in the 34401 review. Same bozo plugged machine on 220 while it was set for 110 ... kablooie...
This one sadly has an open winding in the pirmary ... game over.
I'll see if they sell the transfomers. if it's only 100$ or so it's worth fixing.

Might be worth rewinding it  with this machine. It would cost me here around $100 to do so.

If it was set for 110 there might be enough primary left to still run it on 110?


Did you get it from Finland ?

I was bidding "lightly" on eb.. for one , with a dead primary.
But dropped it , when i found out the trafo was multiwindings.


My 3640a also has defective transformer, the primary was interrupted, try to get it from Agilent but no luck as they don't sell these. I dismounted the transformer and found out the problem was because of a temp fuse located on the outside of the primary winding. If you manage to get the inner bobin out without damage you can easly repair the fuse.

Success and best regards..


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