WTB HP/Agilent/Keysight Pulse Modulator module from 8657 series signal generator - Page 1
Forum section: electronics / general

author: DianaS
author_rank: Newbie
timestamp: August 10, 2019, 06:29:04 pm
content: The Pulse Modulator has failed in my 8657D signal Generator. The Part Number is 08657 67215 or alternatively the complete A 10 board provided it has the modulator module which was an option.The restored (repaired) HP code is 08657 - 89004Diana

author: cathoderay
author_rank: Newbie
timestamp: February 27, 2020, 07:07:27 pm
content: Hello:My 8657B also has a defective pulse modulator. If I knew how to open it I could try to fix it. Did you try to do that already ? Thanks.

author: DianaS
author_rank: Newbie
timestamp: February 27, 2020, 07:14:46 pm
content: HiYes I did open the pulse modulator module - unrepairable!, simple to open with a bit of heat as it's soldered.I managed to pickup a pair of Macom GaAs Fet MMIC's which I plan to transplant into the module connected in series to achieve the right amount of isolation, In the meantime I've bypassed the module.Diana

author: cathoderay
author_rank: Newbie
timestamp: February 27, 2020, 07:28:34 pm
content: Hello:Thanks for answering. Could you describe the defect you found in your pulse modulator ? Mine is clipping the waveform on the positive half-cycle at around +600 mV. Thanks.

author: DianaS
author_rank: Newbie
timestamp: February 27, 2020, 08:21:50 pm
content: Hi,The output level was all over the place..Diana

author: cathoderay
author_rank: Newbie
timestamp: February 27, 2020, 11:06:04 pm
content: Hello, Diana:I opened the modulator; there are two devices I never saw before ( I suppose they are FET switches ) and some discrete logic. The devices are connected in series and seem to have one input and two outputs; they are controlled by signals applied to two separated pins, one complementary to the other and swinging from 0 to -6 V. The devices are marked "21912" and "SW 881". Web search returned nothing useful for these two references. Everything seems fine except that there is clipping on top of the positive half-cycle for an input signal greater than 3,7 Vpp. Perhaps you have more experience than me on these strange devices. Do you have any information on these, that you can share with me ? Thanks.

author: DianaS
author_rank: Newbie
timestamp: February 27, 2020, 11:14:51 pm
content: Hi,In all likely hood they are made by Macom with obscure part numbers.I suggest you junk the modulator and bypass it, unless you really want a pulse output in which case substitute the parts inside it, keeping the case.Incidentally there is an A10 board on eBay, which is being sold as a pulse modulator board, clearly someone has assumed it is a pulse modulator board, - well your out of luck as it's not as the pulse modulator module is missing!!, so it's an A10 board without the pulse facility.Diana

author: cathoderay
author_rank: Newbie
timestamp: February 28, 2020, 06:15:54 pm
content: Hello, Diana:Thanks for your help. I checked M/ACom website and "SW" is prefix for a series of RF switches. No information for SW 881, but I found a SW-226/227/228 which have the same package and pinouts as the SW 881. Unfortunately $ 188.00/ piece is far from my pocket. However, they have other switches much more affordable ( ~ $ 1.00 / piece ) which could be used in place, although some mechanical issues will come because they have a different, plastic package.

author: DianaS
author_rank: Newbie
timestamp: February 28, 2020, 06:59:39 pm
content: Sent you a link to a suitable cheap alternative, the only problem is the isolation is potentially 46 to 38dB, which probably isn't enough, so two is series would probably be ok.They are directly compatible with the supply to the existing HP module being single ended supply.Diana