HP/Agilent ESG 4433B repair info needed [FIXED]

[MarkL]

I have an Agilent ESG 4433B with the UND dual-arb feature.  While trying to use it a couple of weeks ago to generate a multi-tone signal, I got garbage out.  The screen capture below *should* be two clean tones, centered on 1GHz +/- 5MHz.  It was created using the MTONE feature.  Each power on/off cycle creates different garbage.  With dual-arb off, everything works fine.

After a while it will correct itself without touching anything, or sometimes it will generate the correct signal after programming the dual-arb directly and setting up a sequence which includes the auto-generated I/Q pattern created by MTONE.  I cannot figure out any repeatable series of actions that will cause proper operation.  When it starts working, it appears to be random.

I've tracked the problem to the I/Q pattern sequencer on the UND board.  It is a finite state machine implemented with various 74xx series logic and high speed SRAM.  It should be repairable.

There's no surprise that the I/Q output pattern generated by the UND board is also garbage.  It's highly likely the FSM is accessing I/Q segments in uninitialized memory.  It does not seem to recognize where the end of the sequence occurs in SRAM.

I've managed to figure out almost all of the FSM, but debugging has been very slow because: 1) there's no schematic or theory of operation available, and 2) probing is very difficult when the UND board is inserted in the chassis.


Does anyone have a service manual or schematic for the UND board?

Would anyone be willing to probe some points on a working UND board?  It would require taking the bottom shield off the card cage to get as close as possible to the SRAM.  Even when mine starts working, I'm not confident the FSM is doing the right thing and it may be working by random chance.  I'd like to compare with a known working board.


EDIT: Shortly after I posted this, it started working again.  Added screen shot below.  This is driving me nuts.

[nctnico]

I'd check the solder joints closely. Another option is to measure the resistance to ground and VCC for the pins. If an input or output is bad it can be found that way. AFAIK there are no schematics for these machines but I managed to fix several problems in a similar HP RF generator using the block diagram from the service manual.

[MarkL]

I'd check the solder joints closely. Another option is to measure the resistance to ground and VCC for the pins. If an input or output is bad it can be found that way. AFAIK there are no schematics for these machines but I managed to fix several problems in a similar HP RF generator using the block diagram from the service manual.

For the sequencer area, the "service manual" shows two rectangles with one line connecting them.  One rectangle says "Sequencer" and the other says "Sequence RAM (64k)".  Extremely lame.  Plus, the sequence SRAM is actually 128k (Cypress CY7C109D), so even that isn't right.

I too thought it could be mechanical or a solder joint.  I spent a fair amount of time poking at the board with no correlation.


The problem was a bad SRAM chip (U320) in the sequencer.  This particular chip is responsible for one bit of the segment address, the two sequence markers, four bits of the repetition counter, and the end-of-sequence flag bit.  In other words, a little of everything across the total of 32 bits output by the sequencer to really make a mess out of the waveform and spread the suspicion across many related components.

I found the problem by noticing there was only one write to the sequence SRAM to address 0 on waveform startup, yet the sequencer was looping through multiple addresses.  The other addresses contained garbage because they had not been initialzed.  Only address 0 had been set up properly by the firmware.

Further investigation showed that the end-of-sequence bit would properly be set to 1 at address 0 when the waveform was initialized, but then the bit would randomly revert back to a 0 within 30us to 500us.  This caused the sequencer to play out the uninitialized memory beyond address 0.

It seems likely other bits and/or addresses had this issue also, which explained random changes in the waveforms I started to notice.

Occasionally, the bad SRAM would settle to a condition where it would repeat the proper segment, and the unit would appear to work.  However, if I had loaded an I/Q pattern with any complexity, it would have certainly failed to play properly.  The built-in multi-tone waveform I was using only needed a simple single-step sequence, so chances were much better it could fail, repeat this one sequence, and appear to be ok.


One take-away lesson: I bought this unit after checking there was a service manual for it, as I do for most used equipment from ebay.  I did not discover it was only a Service *Guide* (a.k.a. Assembly Level Service Manual), until I really needed it.

[MarkL]

While looking for something else, I came across this service note:

  http://literature.cdn.keysight.com/litweb/pdf/E4433B-11.pdf

It appears that bad sequencer SRAM is a known problem with the UND boards.  And for added fun, this service note does NOT show up when you use the service note search page.


In my repair, I only replaced one SRAM chip.  I'm not a believer in prophylactic parts replacement, but if it's bad enough to warrant a service note with a pre-packaged kit of four replacement SRAM chips, I'm going to replace the other ones on my board.

And as this post correctly points out:

  http://www.keysight.com/owc_discussions/thread.jspa?messageID=122443&#122443

There's four more SRAM chips with the same part number and, on my board with the same date code, that are used by the DSP.  I don't see why they would be exempt from the same failure, so I'm going to replace them too.

Below is a photo of the bad SRAM chip w/date code.  I'm using CY7C109D-10VXI for replacements.  It's a little faster (10ns vs. 15ns) and doesn't matter in this circuit.


If you do a parts lookup of the SRAM replacement kit (E4400-60753) referenced in the service note, it applies to the following products:

    E4430B
    E4431B
    E4432B
    E4433B
    E4434B
    E4435B
    E4436B
    E4437B

So, heads up to all you ESG dual-arb (UND option) owners.