Electronics > Repair
Wavetek 2520a 0.2-2,200MHz RF sig gen repair
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dazz1:
Hi
Ran the Wavetek 2520a and connected Siglent SSA all day to do a burn in test to flush out any more defects on the 2520a, and to stabilize the crystal osc on both instruments.
The 2520A is fitted with a 10MHz OCXO. 

The tolerance for the frequency is +/-2.5ppm.    This translates to +/-25Hz for the 10MHz reference.

The measured relative difference between the 2520A and the Siglent is 12.6Hz, but I don't know what the Siglent reference error is.    What I can say is that the OCXO is likely to be within tolerance, and if it isn't, there is a calibration and frequency adjustment procedure I can follow based on a more precise time reference.

Of course all of this points to falling down Alice's rabbit hole trying to find true time.

So all tests done to date indicate the 2520A of fully functional with all faults cleared except for the failing nvram.  A replacement is on order.

Dazz
tautech:

--- Quote from: dazz1 on July 01, 2021, 07:04:17 am ---Of course all of this points to falling down Alice's rabbit hole trying to find true time.

--- End quote ---

Come back Dazz !  :-DD
Zero999:
Wow I didn't know there was such as device capable of going from 0.2MGHz which is IR, through to 2200MGHz, in the hard X-ray region. :P
dazz1:
Hi
For the benefit of others that may need to repair/restore a WaveTek 2520A, attached is a copy of all the eproms of my one.
These are version 5.1 of the firmware. 
The file names include the chip number on the PCB and the component id.

There is one eprom that stores the values of sine waves, for the frequency synthesis.
There is one eprom that is installed on the GPIB board, if this option is installed.  It probably is.
There are 3x eproms that hold the firmware on the board with the 6805 processor. 

The files are in intel hex format.

I have copied the eproms onto Atmel TMS27C256-R-70PU one time programmable devices.  They are almost pin for pin compatible.
I replicated the firmware from the TMS27C128 devices because pin 27 is address A14 or PGM depending on the device.

For the TS27C64 replacement by the TMS27C256, I soldered a link between pins 26 and 27 directly on the memory device.  This meant I could fit either the original or the replacement device without modifying the PCB.  It should be possible to link these pins on the pcb and still swap because on the 64kb eprom, pin 26 is NC.

I took a great deal of care to avoid risk of static discharge wrecking the chips.  Now I have a copy of the original eproms, the plan is to replace them with the otp eproms.  If I have a problem with those, I can revert to the original eproms. 

Thanks to Tautech for organizing the eprom programmer loan from The Def Pom.  They used to be so common but are now surprisingly rare.

I have programmed the new otp eproms, but I have not yet installed them.  The 2520A has developed a new fault.  Prior to removing the original eproms to copy them, I switched on the 2520A to check that it was OK.  This showed the LCD display flashing randomly.  The LCD display segments are driven by a number of driver chips, so whatever is causing the problem affects them all at the same time.  This points to a bad joint or an unstable power supply.  I need to investigate.

Doing a power-on check proved to be a really good idea, because I know that the fault was not caused by removing, copying and replacing the eproms.  The symptoms did not change.  If I had corrupted the firmware while copying, the 2520A would be bricked.  The amount of effort required to reverse engineer the firmware to find and fix the corrupted code would have been too much effort to justify.

I suspect this 2520A has been sitting around for years and things have deteriorated.
Applying power has revealed a cluster of defects.


Dazz
dazz1:

--- Quote from: Zero999 on July 01, 2021, 01:54:11 pm ---Wow I didn't know there was such as device capable of going from 0.2MGHz which is IR, through to 2200MGHz, in the hard X-ray region. :P

--- End quote ---

Do you know how long it took me to edit my posts ???    :(

Dazz
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