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EIP 545B Frenquency counter
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douardda:
Fun fact: in fact, the power meter is working "out of the box". When I activate it, it display the triple E for a few seconds, then display a power (obviously completely uncalibrated) with a "resolution" of 3dB, since the second AD7526 (U12) is not present.

So I've installed an AD7526 in U12 socket, a FH1100 equivalent diode (a QSCH1245) and removed R39, et voilĂ ! the power meter now works with the 0.1dB resolution!



Now i need to figure out where the calibration curves are stored in the memory. I don't think it's located at the same address as it was on the 545A (0x4000 in the EPROM that can be installed on A107) since the ROM on the CPU board do have content in this 0x4000->0x47FF mem area.

It might even be located in the EEPROM.

I still have a few issues I need to fix:

- I've replaced the CR4 zener diode on A107; it was dead (open), but the sensibility remains too low on band 3 (I can sometimes "catch" a signal at -15dBm or so, but it's unstable). The reference voltages on pin 2 of U14 (LM393 comparator) is now a stable -100mV as described somewhere in the service manual, but the signal detection circuitry is still not working properly. I need to double check the capacitors on this A107 board, since a quick in-place check with a DER DE-5000 LCR meter showed some strange results for some of them (surprisingly, not the tantalum ones, but I'll check theses again with a lead desoldered from the board).

- When I power the device, it's set with a 200MHz offset and only 5 digits of resolution. I guess this is the part of the "SPECIAL WB68" version of the firmware I have, but I find it quite annoying.

- Replace the bent BNC connector for band 2.

- And run a deep check / calibration of the unit.
 
I've started to (partially) disassemble the firmware to find where I need to change these initial values. Dawn it's been a looong time since I've played with 6800 assembly code! I was also trying to figure out how to activate the power meter, but this is now magically fixed :-)

I'll write a follow up on my blog with the things I've understood in the disassembled firmware when I'm done.

David
edpalmer42:

--- Quote from: douardda on January 12, 2018, 11:38:31 pm ---I still have a few issues I need to fix:

- I've replaced the CR4 zener diode on A107; it was dead (open), but the sensibility remains too low on band 3 (I can sometimes "catch" a signal at -15dBm or so, but it's unstable). The reference voltages on pin 2 of U14 (LM393 comparator) is now a stable -100mV as described somewhere in the service manual, but the signal detection circuitry is still not working properly. I need to double check the capacitors on this A107 board, since a quick in-place check with a DER DE-5000 LCR meter showed some strange results for some of them (surprisingly, not the tantalum ones, but I'll check theses again with a lead desoldered from the board).

--- End quote ---

Have you checked the calibration on the YIG bandpass filter?  If it's out of adjustment, the signal won't get through to the rest of the system or will be badly attenuated.  I have a unit that seems to be made of pieces from multiple systems.  The YIG filter was about as far out of adjustment as it could be!

Ed
douardda:

--- Quote from: edpalmer42 on January 13, 2018, 01:16:40 am ---Have you checked the calibration on the YIG bandpass filter?  If it's out of adjustment, the signal won't get through to the rest of the system or will be badly attenuated.  I have a unit that seems to be made of pieces from multiple systems.  The YIG filter was about as far out of adjustment as it could be!

Ed

--- End quote ---
Yes I've been thinking something like this may also happen. I'll try to check a bit if the YIG calibration is reasonably OK, at least up to the frequencies I can check for now with the equipment I have.

David

douardda:

--- Quote from: douardda on January 12, 2018, 11:38:31 pm ---
Now i need to figure out where the calibration curves are stored in the memory. I don't think it's located at the same address as it was on the 545A (0x4000 in the EPROM that can be installed on A107) since the ROM on the CPU board do have content in this 0x4000->0x47FF mem area.

It might even be located in the EEPROM.


--- End quote ---

Just realized HighPrecision wrote a few posts back the PM calibration table is in the EEPROM... doh! Whatever, I still need to find where.

I've found the tests vector table in the firmware, and there is no other (undocumented) test than the ones listed in the service manual (1 up to 11, 90 and 91). Could have been a 92 or any other value to enter a PM calibration menu but it seems no such menu exists... So one have to burn the values in the EEPROM somehow.
HighPrecision:

--- Quote from: douardda on January 12, 2018, 11:38:31 pm ---- When I power the device, it's set with a 200MHz offset and only 5 digits of resolution. I guess this is the part of the "SPECIAL WB68" version of the firmware I have, but I find it quite annoying.

--- End quote ---
Special WB68 is a BAND 3 Low end frequency extension to 0.6GHz (600MHz) with reduced specs for sensitivity and power meter dynamic range.

Frequency offset and resolution setting have not to do with this special option, in the EEPROM there are saved the instrument power-on defaults.


--- Quote from: douardda on January 13, 2018, 11:15:45 am ---Just realized HighPrecision wrote a few posts back the PM calibration table is in the EEPROM... doh! Whatever, I still need to find where.

I've found the tests vector table in the firmware, and there is no other (undocumented) test than the ones listed in the service manual (1 up to 11, 90 and 91). Could have been a 92 or any other value to enter a PM calibration menu but it seems no such menu exists... So one have to burn the values in the EEPROM somehow.

--- End quote ---
As I said the power meter calibration is NOT part of the standard calibration procedure, there is no related TEST xx for this.

The EEPROM on CPU board is allocated from 0x0800 to 0x0FFF

Power meter calibration table start at 0x0810

YIG DAC calibration table start at 0x0C00, but I have no idea if the special option WB68 start at this location (shifted data ?).

You can use TEST 10 to modify the EEPROM locations, or via GPIB with TA10 command, obviously the write-protect switch should be disabled.

I suggest to save the entire EEPROM before any attempt to change data.


Edit:  typos
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