Marconi/IFR/Aeroflex 2023 2024 2025 Repair advice, Error 502 Fractional N loop - Page 1
Forum section: electronics / repair

author: volvo_nut_v70
author_rank: Regular Contributor
timestamp: August 14, 2019, 12:14:51 am
content: I just bought a IFR 2025, it works just fine until it warms up. Then I get a ERR 502: Fractional-N Loop high.It's has all the hallmarks of a thermal issue. Has anyone dealt with this before?Many thanks in advance!!

author: AlcidePiR2
author_rank: Regular Contributor
timestamp: October 25, 2019, 04:26:04 pm
content: I got a IFR2023a with the same problem.Err 502: Fractional-N loop highAnd no signal in the RF output.I have checked the ref signal on the back BNC outputAs soon as the 2023a is turned on, the 10Mhz square signal appear, but very quickly shut down.See the video (6 seconds)You can hear the clicks of the relays.One can see a review of the IFR2023a in the Eevblog #261But I must say, I have no clue where to search for this fault.

author: AlcidePiR2
author_rank: Regular Contributor
timestamp: October 26, 2019, 11:51:55 am
content: I found some related and interesting information in the eevblog herehttps://www.eevblog.com/forum/repair/quick-repair-project-marconi-2024/msg151502/#msg151502and to a lesser degree, herehttps://www.eevblog.com/forum/testgear/looking-for-schematic-marconi-2031/msg452841/#msg452841

author: AlcidePiR2
author_rank: Regular Contributor
timestamp: June 16, 2020, 11:53:53 am
content: Dear All,I am starting a new attempt to fix this beautiful device, but will need some help. I will really appreciate if someone could guide my steps, as the service manual exists, but is not always very explicithttp://bee.mif.pg.gda.pl/ciasteczkowypotwor/Marconi/Marconi_2023A_2024A_2025_Service_Manual.pdfThe problem is the error message "Error 502 Fractional N loop"This is what I have done so far, following the maintenance manual.QuoteDone : the fault is present al all carrier frequencies . ThusQuoteQuoteVoltage at TP14 is 9.133V

author: AlcidePiR2
author_rank: Regular Contributor
timestamp: June 16, 2020, 01:37:29 pm
content: Quote- 25 Mhz is present on IC205 pin 9- I think there is a misprint here. pin 3 of IC313 has no 5 Mhz, but also no test pad. pin 3 of IC310 has a test pad and 5 Mhz is present.Can someone confirm the misprint ? Or am I wrong ?

author: AlcidePiR2
author_rank: Regular Contributor
timestamp: June 16, 2020, 03:05:43 pm
content: Quote from: AlcidePiR2 on June 16, 2020, 01:37:29 pmI checked again and realized that the error was mine.The numbering is confusing as the IC313 name is on the other side of the chassis separation.When measured at the pin 3 of IC313 we have a 5 Mhz signal with 5.2 V amplitude and 30 ns width.

author: George Edmonds
author_rank: Frequent Contributor
timestamp: June 16, 2020, 03:20:47 pm
content: HiThe first step is to check very carefully for leaking electrolyte SMD electrolytic capacitors, they are a PITA.I have a full printed service manual if the PDF copy is not clear.73 George G6HIG

author: AlcidePiR2
author_rank: Regular Contributor
timestamp: June 17, 2020, 11:49:20 am
content: Quote from: George Edmonds on June 16, 2020, 03:20:47 pmThanks for some feedback. This si supportive in this task. I have checked the SMD electrolytic capacitors. From what I can see visually, they are fine.QuoteThis is good to know. What is the date of you manual ?

author: George Edmonds
author_rank: Frequent Contributor
timestamp: June 18, 2020, 05:22:51 am
content: HiMay I first say that it does not help and adds to the confusion when what should be two separate threads become merged into one.I intend addressing the problems with the one in France only in this posting, given, that it appears to be the simplest/quickest one to fault find.The printed service manual that I have is dated 8th March 1999, exactly the same as the online version.Errors in operators and service manuals are not unheard of, this covers all manufacturers, not just Marconi. Your brain has to be kept active somehow.Having re read the entire posting very carefully and if the information provided is accurate the initial problem with the one in France is clear. It is stated that after a few seconds the 10MHz standard output signal on the rear of the instrument goes missing. This is the first fault to be addressed, without a fully working 10MHz internal standard the instrument cannot possibly work correctly.There are two types of 10MHz standard used in the 2023/2025 range of Marconi signal generators, a TCXO one made by HY-Q and a OCXO one made by NDK (option 4 on serial plate). I have yet to see a faulty NDK standard but this is certainly not the case with the HY-Q standard which do fail. BUT it must be made clear that the problem may not be one the 10MHz standards at all, they rely on the instruments power supply and the support circuitry on the AB1 control board all of which must also be checked and be fully functional.Check that in the Util4 “frequency standard” menu you have option 4 selected, “internal 10MHz out”,There are also two versions of the main instrument planar, which one is being used a AA1 or a AA1/1.At risk of repeating myself, the main problem with these signal generators is the surface mount electrolytic capacitors failing, the smaller the physical diameter of them the more likely that they are to have failed. The smaller diameter ones appear to have problems with the electrolyte seals failing.73 George G6HIG in Dover UK.

author: AlcidePiR2
author_rank: Regular Contributor
timestamp: June 18, 2020, 10:09:48 am
content: QuoteYou may be right, but when I started this, I thought it was better not to multiply the threads on the same subject. Next time, I will do a separate thread for a repair tentative.Now it may be too late to change.QuoteThanks a lot, your input is extremely valuable, as I am quite blind here.QuoteMine is HY-Q ( TCO-1009 10.0Mhz 15/99)QuoteThanks a lot George ! This is one of my mistakes. I had it set to 0. I set Util4 to 4, and now I have the 10 Mhz signal in the rear output ( amplitude needs to be divided by 10as I left the 10x option while using a simple BNC cable).QuoteWhere is this information ? I cannot see it.QuoteI understand. I will check carefully the SMD caps this week-end.Thanks again for the assistance. I hope that with your help I will be able to make this instrument run again.

author: AlcidePiR2
author_rank: Regular Contributor
timestamp: June 18, 2020, 11:38:52 am
content: Quote from: AlcidePiR2 on June 18, 2020, 10:09:48 amNow I have itMy board is 44830/001 so according to P. 6-4 of manual, it should be AA1 ( AA1/1 board is 44830/249).

author: AlcidePiR2
author_rank: Regular Contributor
timestamp: June 18, 2020, 08:49:56 pm
content: Let me continue my search for the fault, following the procedure of the maintenance manual .QuoteIn TP7, I find a pulsed signal, with frequency 10.66 Mhz, pulse width of 30 ns, and amplitude of 5.16 V ( see below) so this is OK.QuoteThe frequency is 10.66Mhz, so not in a condition of likely fault.QuoteThe signal is at 10.66Mhz, thus above 5 Mhz, but the voltage on pin 3 of IC402 is 4.04.Is this Bad ?QuoteHow do I do that ?Thanks

author: AlcidePiR2
author_rank: Regular Contributor
timestamp: June 20, 2020, 02:30:33 pm
content: Quote from: AlcidePiR2 on June 18, 2020, 10:09:48 amI have checked a dozen of the SMD electrolytics ( desoldering it from the board and testing with a transistor tester ( 1.13k))None is totally offThe 100 uF and 47 uF have ESR of about 3RThe 10 uF have ESR of 12R could this be a source of the problems ?I will probably recap the whole thing to be sure.

author: Miti
author_rank: Super Contributor
timestamp: June 21, 2020, 12:15:58 am
content: I just measured some capacitors from my junk box:Panasonic EB series 100uF 50V - 0.22RNichicom UHE series 100uF 50V - 0.025RNichicon UPW series 100uf 25V - 0.170RNichicon UPW series 47uf 25V - 0.638RNichicon UPW series 10uf 25V - 0.648RSo I think your caps are a bit high. How many hours does it have? I have an IFR2025 with 77492 hours so almost 9 years of continuous operation.

author: AlcidePiR2
author_rank: Regular Contributor
timestamp: June 21, 2020, 10:20:17 am
content: The caps are slightly lower voltage10 uF 16 V47 uF 16 V100uF 6.3 VBut I agree that the ESR is too high. I just wonder if this is sufficient to cause the problem. In any case, I will change all caps.I had not check the hours of service of the device. Now its too late, as I will not power it without the caps on. Will look after putting back the caps.

author: AlcidePiR2
author_rank: Regular Contributor
timestamp: July 03, 2020, 08:23:42 pm
content: This unit has 78493 h of operationI have changed all electrolytics from the RF board, and now it is working.I am surprised as none was really off, as I have seen in previous repairs. But obviously, they were the culprits.I wonder also if there was not a bad joint at one of these caps.Thanks for all !