GW Instek SFG-830 fuction generator partial teardown and test screenshots

[nightmechanic]

Hi All,
(my first teardown...)

So,
I was looking for a function generator to add to my small home lab for a while and encountered a GW Instek SFG-830G for sale on ebay, after some price negotiation, I purchased it.
It is a 30MHz (sine BW) DDS arbitrary function generator, QA sticker is from May 1999 which fits the date code of the devices inside. Not such a good era for electrolytic capacitors, see below.

As you can see in the pictures, it uses a Qualcomm DDS chip and an Analog devices DAC. (the DDS chip runs at 42.something MHz and it has a frequency doubler to extend the output range to 30MHz.

And, what could be better than to take it apart and shoot some photos?

the front:



Both (top and bottom) external covers are  grounded:


The main PCBs seem to be shielded very well (lots of screws to open...), this is the bottom one, the shield on the top looks the same.
The top left small PCB is the GPIB add on, the bottom left one is the RS-232 and 2 of the supplies.


The top PCB' s back side:


Top PCB (MCU +DDS), the MCU is behind the cables, it is an Intel 8052. Not too thrilled about the lithium battery (probably keeps the calibration data), living with it on other stuff (3478), add this one to the 10 year replacement cycle 


Top PCB zoom in:


Bottom PCB (more DDS memories and the output amplfier and attenuators(?)):


The sad... two caps on the bottom PCB are leaking...all electrolytic caps will be replaced, fun fun fun...


Over all build quality seems very good, well shielded and organized. Not too thrilled about having another lithium battery to take care of and very unhappy with the leaking caps... But I think it is definitely worth while replacing them.

Some performance screen shots in the next post.

Ran

As requested, the rear panel:

[Hydrawerk]

Please post a picture of the front panel. It looks a bit like Stanford research equipment.
https://www.eevblog.com/forum/testgear/stanford-research-systems-any-opinion/

[nightmechanic]

The front is the first picture, it is somewhat different, I will add a picture of the rear end as well

Ran

[Hydrawerk]

Thanks.

[nightmechanic]

I took it to work (where there are better/newer scopes than my 54645 (which I like a lot!, no insult intended ) and some spectrum analyzers as well...) and and spent some time (afterhours ) in the lab to see what this machine is up to.

Sine frequency domain:
1kHz harmonics and spectrum:


10kHz harmonics and spectrum:



100kHz harmonics and spectrum:


1MHz harmonics and spectrum:


10MHz harmonics and spectrum:


30MHz harmonics and spectrum:


Over all sine harmonics seem to be well within specs.

Now some time domain:

555kHz square wave rise and fall (5Vpp):


10kHz triangle:


100kHz triangle:


10kHz 5Vpp square wave overshoot and rise time:


1MHz 5Vpp  square wave overshoot and rise time:


The overshoot is a bit high (7% compared to the 5% spec) and the rise time is just about there (16nsec vs 15).
I will check it again after the capacitor replacement and try to tune it better if I can (according to the manual there are adjustments for these).

p.s. While testing it, I noticed that it seems to be getting a little hot, I will open it up and check what is heating, could be related to the caps as well (hopefully - easy and planned fix anyway )

Ran

[nightmechanic]

Please post a picture of the front panel. It looks a bit like Stanford research equipment.
https://www.eevblog.com/forum/testgear/stanford-research-systems-any-opinion/

I added the rear panel photo to the first post.

Your observation made me curious, so I searched and found the service manual with schematics for the Stanford research DS-345. I would call them is a non identical twins.

Everything digital (mainly MCU and DDS ) up to the waveform DAC is functionally similar but not identical, e.g. The DS-345 uses a Z8800 MCU while my SFG-830 has a 8052, DS-345 has its own ASIC DDS(?) and a TRW TDC1112 DAC, and the Instek uses an off-the-shelf Qualcomm DDS chip with a Qualcomm / Analog devices DAC.
The feature set is also different with the DS-345 offering more with built in noise generation, burst operation, 1uHz resolution (vs. the 20mHz resolution the SFG-830 offers).

However, from the DAC output to the BNC connector, the 2 generators are identical (I didn't go through every component but several random ones in each page) including transistor and opamp part numbers, passive component values, the filter transformers, the DACs used for amplitude and DC offset control, the AD586 shared power supplies reference etc. amazing.

I wonder if it is shameless copying or some sort of cooperation? (And why the XXXX did they have to copy Lithium battery... )

Thanks for pointing this out.

Ran

[picburner]

I know it's been a long time and you may not have this instrument anymore, but if so, could you take a picture components side and solder side of the GPIB board? Thanks.
(Or someone else with this same instrument)