492P signal amplitude error and error 58


Attilio
 

Hello everybody,
I received the spare 1st LO YIG. I replaced the 1st LO YIG on my 492P and it worked again without error 58. I had to recalibrate the 1st LO driver board and the LOG and AMP controls on the front panel. I also had a problem on the A54 memory board (the version changed from 1.6 to 1.5 with the command lock on the front panel), solved by replacing an IC HD74LS07 on the A54 Memory Board (my A54 Memory Board is modified with only one EPROM 27C512 and two additional HD74LS07 buffers, the EPROM contains version 1.6 for 492P).

Thanks for the support.

Best Regards
Attilio


Attilio
 

Thanks Bob,
I cannot locate the NEC mm765 RF amp or the uPC1764A in the 492P.
As soon as I get the spare, I try to replace the 1st LO YIG.

--Cheers
Attilio


W1RS
 

I don't have a 492P, but while searching for a datasheet for some parts I have I saw that somebody was looking for an NEC mm765 RF amp that is used in this instrument. It is also known as upc1764A. If you find out that this might be the problem, I can supply you with NOS parts.

Good luck ,
Bob


Attilio
 

Is the YIG oscillator the 1st LO ?
Unfortunately I don't have a power meter to measure the power-level out of the YIG oscillator.
I could take a spare 1st LO and try to replace it.

--Cheers
Attilio


ulf_r_k
 

I am sorry to hear that replacing U1050 and U2050 did not help.

What is the power-level out of the YIG oscillator?

BR

Ulf Kylenfall


Attilio
 

Greetings everyone,
I have tried replacing U1050 (74LS74) and U2050 (74LS10) on the A50A3 offset mixer board, but without success.
I also tried to replace the 1st mixer, but nothing has changed.
On all span / div the signal amplitude is low compared to the correct value (for example the amplitude of the calibrator of - 20 dBm is indicated as - 43 dBm, the frequency is correct).
Also the error 58 related to Phase Lock mode actually comes out when the 492 P tries to enter in this mode, but fails and indicates "Error 58", even the LED on the "PHASE LOCK" button never lights up.
What could I check?
I suspect it could be a problem with the 1st local oscillator or its driver.

Thanks for your attention.
-- Cheers
Attilio


Attilio
 

Thank you very much, I try.

--Cheers
Attilio


ulf_r_k
 

Having experienced the same problem with a 494P I read somecomments about this on KO4BB -site.
I ended up replacing U1050 (74LS74) and U2050 (74LS10)on the A50A3 offset mixer board. I hesitated at first but usedlow profile high quality DIP sockets and the analyzerworked OK after this.
All the best.
Ulf KylenfallSM6GXV


Attilio
 

Happy Easter everyone,
my 492P was working when error 59 and then error 58 appeared for a moment on the screen, at the same time on all span / div the signal amplitude is low compared to the correct value (for example the amplitude of the calibrator of - 20 dBm is indicated as - 43 dBm, the frequency is correct). Error 58 is related to Phase Lock mode and actually comes out when the 492 P tries to enter in this mode, but fails and indicates "Error 58", even the LED on the "PHASE LOCK" button never lights up.
I checked the power supply voltages and they are within tolerance, I checked some components on the A4 and A5 boards (R3011), but without finding any problems. The suspicious thing is the error in the amplitude of the signals displayed at the same time as error 58. I think maybe the fault is not in the phase lock circuits but elsewhere, but I have no idea where.
Unfortunately I don't have the extenders for the 492 P boards.
I don't think it's a 1st mixer problem but it looks more like something in IF circuits.
I need help to fixing the fault.

Thanks for your attention.
-- Cheers
Attilio