Electronics > Repair
Wavetek 2520a 0.2-2,200MHz RF sig gen repair
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dazz1:
Some more photos

The 1st photo is the new cable assembly in-place.  It is and looks better than the factory original.
The 2nd photo shows 4 of the 5 otp eproms installed.

All of the otp eproms are 256k compared to the original 128k.  The only thing needed to make these work was to fill up the 256k devices with duplicate copies of what was on the 128k device. 

The sine wave table for the synthesizer was stored on a 64k eprom.  For this, 4 copies of the eprom fitted in the 256k device. I also soldered a bridge wire directly across pins 26 and 27 of the 256k otp eproms. No changes required to the pcb.
dazz1:
Hi
Just a couple of photos.

The wire link soldered directly to the 26-27 pins of the 256k otp eprom (follow arrow) to make it plug-in compatible with the 64k eprom it replaced.

Confirmation that all the otp eproms are working.  There are 3 ROMs with code in them.  They switched in/out depending on the mode.  It is possible that the 2520A could have passed all its self-tests in calibration mode, while the operating ROM was defective.
Note that the 2520A passed all the eprom (parity ??) tests so that possibility should be impossible. 
dazz1:
Hi
I replaced the Dallas battery backed nvram today with a modern equivalent.  When the 2520A was powered up, it displayed error messages. Not surprising.
I went through the diagnostics routines which includes loading default settings.
Everything went swimmingly except for one small detail.  The "Options" self test failed.


I suspect that the nvram still retains some memories, which includes the options are installed on this particular 2520A.  When I swapped the nvram, the memory of those options remained on the old nvram. 
Given that there is no connector that would allow an external device to read/write to the nvram, and given the vintage of the 2520A, I suspect that the front panel keys are the only way to write to the nvram. 
If that is true, then it is likely that the ROMs include the routines necessary to make the options usable.   

My theory is that there is a secret command entered on the key pad that enables specific options.  It is probably a variation of the key commands to run the diagnostics and calibration routines.   Testing that theory probably requires disassembly of the firmware code.  I think that would be challenging to say the least.  Additionally, I don't know what options are now missing.  There are factory stickers on a couple of option keys.  One is for external phase modulation.  The other is to specify units of rad.  It is unlikely I would use either of those options, which I think are related and part of the same option.   

It would be nice to restore the 2520A to its full operation.


EDIT

I found a description on the Phase  Modulation feature in the Operator Manual, now attached.


khs:
Here a 2520-SP782 with up to 2.7 GHz. All looks similar.
But it looks they have made some modifications regarding the RF attenuator...

It looks the schematic of the GPIB interface is a big secret, so there is no way to add the missing GPIB interface...
dazz1:
Hi
Definitely different to mine.  Your firmware is ver 8.3, mine is 5.1 but the dates on the boards look older than mine.   Maybe yours was factory upgraded??   I wonder if any two of the 2520A are the same?

I have considered the possibility of modifying mine to have a higher frequency limit but reverse engineering the firmware would be just too much work.    Wifi would be within the 2.7GHz range but I don't know if the phase modulation feature I have (currently not enabled) would be useful.   It would require a computer ahead of the sig-gen to generate the base band signal, and a receiver.

It wouldn't be too difficult to reverse engineer the GPIB board because it is only 2 layered and I have posted a copy of the GPIB  firmware but figuring out how enable that option in the main firmware would take time and effort. 




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