Rohde Schwarz SMIQ problems with IQ modulator - component ID - Page 1
Forum section: electronics / repair

author: dhillman
author_rank: Contributor
timestamp: October 08, 2016, 04:11:49 pm
content: My once working SMIQ04 would not pass internal alignment the other day citing errors on ALC and level preset. These were not the usual errors that surround the dead battery issues, instead the control voltages were 'OOT'.Looking further, I found that test point 2109 (D_AMOD) tuning voltage AM modulation was at 13.95V. The expected range being 0.02 - 6.0V. Slightly horrible!Checking out the AM modulation input from the convenient legend:Further investigation:Now my question to all of you out there who may own a SMIQ, have access to the board layout CAD files, and or schematic, could you please clue me into the values for the burnt components? I suspect they are all resistors for amp bias, but who knows. I tried extrapolating the component designations from the x-y coordinates from the service manuals online, but soon realized this was a great way to get to sleep.Thanks!Edit: Sorry about the image hosting.. I will find something better.

author: dhillman
author_rank: Contributor
timestamp: October 10, 2016, 04:03:32 pm
content: These four resistors in parallel are the drain resistance to the SHF0189.I'm going to go on the assumption that the HFET is damaged and replace it. Unfortunately I cannot leave the unit on to check the gate bias as these poor drain resistors register over 120Celcius on the thermal camera when powered.Anyhow, if anyone can ID the resistor values in their SMIQ, I'd be greatful.I'm thinking that they are the same value and may be 30ohms should the one with a remnant of a part number be valid.The existing SMIQ service manual on the net is for an older revision it seems.

author: rastro
author_rank: Frequent Contributor
timestamp: October 11, 2016, 06:11:36 pm
content: Hello dhillman,Have you looked at the 4 volumes of SMIQ service manuals available at:http://www.ko4bb.com/getsimple/index.php?id=manuals&dir=Rohde_SchwarzI think the IQ Modulator is in volume 2.There are no schematics but they do have a parts lists for the boards along withcoordinatesof the part location on the board. I thinks the origin is lower left with the top of the board facing up. of course if you're looking at something on the back of the PCB then you need to mirror image.-rastro

author: dhillman
author_rank: Contributor
timestamp: October 12, 2016, 01:42:03 am
content: Hi Rastro,I have scoured the available service manuals on that and other sites. Unfortunately, as others have found, they are for a previous HW revision than the many SMIQxxB's out there including mine. As such, the amplifier chain on the IQmod board uses different HFETs and different bias networks.Dan

author: JFJ
author_rank: Regular Contributor
timestamp: October 12, 2016, 10:35:31 pm
content: Quote from: dhillman on October 10, 2016, 04:03:32 pmI looked at the resistors on my IQ-Modulator. Unfortunately, two of the four paralleled resistors have no ID markings (presumably, they're a different value to the other two). As I'm unable to take a close-up photograph of my unit, I've annotated part of your picture with the resistor markings that I could see:

author: rastro
author_rank: Frequent Contributor
timestamp: October 13, 2016, 01:03:40 am
content: Quote from: dhillman on October 12, 2016, 01:42:03 amIt would be helpful to post the part number and rev level of your board since you say there are significantly different configurations out there.Anyway it looks like you have some help.I wonder if those unmarked SMD resistors where just mounted upside down???Have you un-soldered your burnt resistors to look underneath on the off chance there's some surviving markings underneath?-rastro

author: dhillman
author_rank: Contributor
timestamp: October 13, 2016, 04:55:22 am
content: Thank you, JFJ, for the details from your board.To rastro: If time permits, I will extract the parts tomorow and see what is found. I may luck out and find that they were placed upside down. That would be a shock given R&S care to detail, but you never know.

author: jgorsk
author_rank: Regular Contributor
timestamp: October 13, 2016, 10:03:30 am
content: I hope this helps

author: dhillman
author_rank: Contributor
timestamp: October 14, 2016, 12:50:05 am
content: Quote from: jgorsk on October 13, 2016, 10:03:30 amI removed the resistors from my board today, and three of the four were consistent with the values on your board. One was open.I've been trying to determine what SMD code is used on the '1:R' etc. parts. Not of consequence. Once the replacement HFET's and resistors get here, I'll see where I stand. A quick check of gate biasing is in order before the FET goes in though!

author: rastro
author_rank: Frequent Contributor
timestamp: October 14, 2016, 03:49:12 pm
content: Just wondering if any of the SMD resistors mounted with marking facing the PCB (upside down)?-rastro

author: dhillman
author_rank: Contributor
timestamp: October 14, 2016, 11:02:42 pm
content: Quote from: rastro on October 14, 2016, 03:49:12 pmNo, they were not upside down.I have the new resistors in place. The drain voltage is around 6.5V, and the gate voltage does a quick bounce to -2.3V, then back to zero.If I had the schematics I could get a good idea if this was by design or not.The SHF0189 will be showing up on Monday...

author: dhillman
author_rank: Contributor
timestamp: October 15, 2016, 04:44:18 pm
content: Quote from: dhillman on October 08, 2016, 04:11:49 pmI decided to acquire the actual service manual for the SMIQB with schematics (for a cost). I was intrigued to discover that the manual freely available on the usual sites is in fact for a different revision. Even the test point voltage ranges are different. The resistances of the drain resistors provided by JFJ match the service manual, so I have that repaired as it should be.

author: rastro
author_rank: Frequent Contributor
timestamp: October 16, 2016, 01:55:00 am
content: I didn't know that R&S would sell the full service manuals.What is the "SMIQB" is "B" the next revision level for the system/documentation?-rastro

author: dhillman
author_rank: Contributor
timestamp: October 17, 2016, 11:38:07 pm
content: After replacing the drain resistor and the amplifier, the unit will again calibrate.I know the board needs a de-linting of swab remnants!

author: rastro
author_rank: Frequent Contributor
timestamp: October 18, 2016, 01:06:48 am
content: Great news.

author: jgorsk
author_rank: Regular Contributor
timestamp: October 18, 2016, 08:50:54 am
content: Good job. Did you get the service manual with the schematics and the assembly drawings? Where did you buy it? I tried to buy it from R&S but they said that it's not available anymore.

author: m-e-t
author_rank: Newbie
timestamp: October 28, 2016, 03:26:56 pm
content: hello i m face to same problem as well IQ error, but there's different version of same board A240 IQ-Modulator 1084.9800 and 1084.9800.02the 9800 is different from the one you describe , what ref do you've in hand?i m working on smiq03b with lot of options in , difficult to indentify the problemthanks sebastien

author: dhillman
author_rank: Contributor
timestamp: October 31, 2016, 11:28:20 pm
content: Quote from: m-e-t on October 28, 2016, 03:26:56 pmHi Met,The version that I have is 1084.9800.10. The service manual that is free on the net is for 1084.9800.08. Sorry, but I do not have details on yours. Do you have a picture of the board that you can post?Dan