LEVEAR/PANASONIC VP-8193D SIGNAL GENERATOR OUTPUT FAILURE when output >100dBuV

[HIFI LOVER]

Hello,

Bought some while ago this Levear/Panasonic VP-8193D signal Generator.
everything worked well, but i never used output signals higher than 100dBuV.
Now i did need a higher signal, and i found that my output signal collapsed when i adjust the output signal any higher than 100dBuV
by Jog or direct input the problem is the same.
Anybody knows something about this problem??
Like to hear

[Roehrenonkel]

Hi,

please stop screaming at us.

[Benta]

"HIFI LOVER", as you didn't get it the first time:
All-caps headlines and posts are really, really bad style and turns people off.

[coromonadalix]

i've sent a pm earlier this day ... to politely educate

[cosminrodu]

You should hook it up to an oscilloscope in order to see what's going on. 
The output RF amplitude is obtained via a series of attenuators and amplifiers. Here's a rough description.
The finer steps in the output RF level are obtained by varying the dc bias level that is injected in the RF block via the AM input.
If you inject an AM signal it will swing above and below this dc bias level.
This DC bias level needs to be there throughout the entire frequency range of the instrument as it's responsible for keeping a set of PIN diodes polarized.
This signal is controlled digitally and obtained via a DAC and is responsible for -4 db and sub increments.
Aside from this it has a set of 3 fixed, digitally controled attenuators on the RF board that do -20, -10 & -5 db attenuation.
Adding to that, on the attenuator board ( the small can containing the BNC connector) it has a -50, -40 db attenuator plus a +20db amplifier, all of them turned on and off by the digital board.
By using all of these in different combinations the digital board can vary the output signal from -20 to +126db in 0.1 db increments.
Mind you, the +20dB amplifier kicks in above 106db and is hooked in circuit via a relay, you can hear it click when going from 106 db to 107 db.
I have a VP 8194 that had the +20dB amplifier toasted ( among other things) and above 106db no signal was present whatsoever.
My guess is that your unit probably has one of the attenuators broken.
If you need a service manual let me know.