| Electronics > Repair |
| R&S SMS repair, progress made but stuck on Y4 board fault ? |
| (1/1) |
| RichardM:
Hi All, Made progress on turning 1 x working and 2 x non-working R&S SMS signal generators into 2 x working units. Replacing all the Roederst plastic cased capacitors helped the progress, maybe 10% were bad/leaking. Also, 2x bad 8049 microcontroller chips, one bad TTL chip and 2 x dead P8279 keyboard controller IC's (are there prone to fail ??). I still think I have an issue with the attenuators, but to isolate/troubleshoot/eliminate all the plug in circuit boards I have decided to use my one good unit as the guinea pig. I have been systematically testing each board Y1 to Y8 in the working unit and it appears there is a fault on the Y4 board which is identified as the Phase Control board. Unfortunately, it is marked 302.5890 which is not described in any of the service manuals I have been able to find online. These manuals discuss at length the Y4 302.5819 which looks quite different to the Y4 boards I have. I have found the correct schematic (attached) but not a manual that describes this revision of the Y4 board. Anyway, this is what I am seeing at the RF output on the front - 0.1 to 8MHz output is fine, at MP1 it equates to f(MP1)=(40-fout) > 8 to 19.999MHz output is incorrect, approximately double the frequency 20 - 48MHz output is fine >48MHz to 71.999 output is incorrect 72 - 99.999 output is correct 100 - 111.9999 output is incorrect (shows exactly 132MHz when it should be 100MHz) 112 - 154MHz output is correct >154 to 185.999 output is incorrect (shows 139MHz when it shold be 155MHz) 186 to 194.999MHz output is correct 195 to 199.999 is incorrect (shows 183Mhz when it should be 199Mhz) 200 - 214MHz is correct although my scope is limited to 200MHz!! Simply replacing the second Y4 with the Y4 from my working unit fixes the problem, so it must be a fault on the Y4 ? I believe I have tested all the TTL and opamps, and the transistors test ok on diode mode. Any suggestions appreciated as I now begin to test inductors and resistors etc. Regards Richard rohde-schwarz_sms-2_sch (1).pdf (6681.24 kB - downloaded 15 times.) Y4 Block diagram.JPG I have tried 3 times to make this post, I hope it does not appear multiple times!! |
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