Danish RE-125 AM/FM Signal Generator - Page 1
Forum section: electronics / repair

author: whirligig
author_rank: Contributor
timestamp: December 13, 2021, 05:31:26 am
content: I recently bought this RE125 a couple of months ago and have sucessfully aligned two stereo receivers with the last one encountering problems with the RE-125's output. I was able to work around the problem. This unit spans 100 khz to 250 mhz and will modulate AM, FM mono, and FM stereo.The problem is the output would change from a continuous wave (CW) to something resembling extreme FM modulation but it's garbage. The attached photos will show the signal generator, the continuous wave on the scope at 89 mhz, and the garbage output at 90mhz to 98mhz. It will return back to CW after 99 to 102mhz and will remain CW until 120mhz. I surveyed the entire band and the garbage output occurs in a number of areas. It will appear from 38 to 44mhz, 70 to 81mhz, 90 to 98mhz, and 120 to the end which is 250mhz.Has anyone ever encountered this with signal generators in general? I tried tightening up the cable connections with no improvement. What I plan to do next is go through the keyboard menu and clear out any setups in memory. If that does not work, then disconnect the modulation module from the analog unit and see if it's the module. If you have any other suggestions or insights into this problem, let me know.Thanks.

author: 1audio
author_rank: Frequent Contributor
timestamp: December 13, 2021, 05:52:12 am
content: A quick guess is that a phase lock stage is out of range on some frequencies. If you can find a manual its probably an adjustment.

author: picburner
author_rank: Frequent Contributor
timestamp: December 13, 2021, 08:34:06 am
content: Nice instrument.You can find user and service manual at thislink.Probably the two service manuals can help you solve the problem.

author: whirligig
author_rank: Contributor
timestamp: December 13, 2021, 04:17:13 pm
content: Quote from: picburner on December 13, 2021, 08:34:06 amYes, I do have the pdf's of the manuals. They were the deciding factor in buying the instrument.Quote from: 1audio on December 13, 2021, 05:52:12 amPhase lock, that explains what I'm seeing. I will check that out and report back.Thanks everybody.

author: whirligig
author_rank: Contributor
timestamp: December 17, 2021, 05:44:15 pm
content: After perusing through the manuals, I found the phase lock stage is located on one of two synthesizer boards. To make any adjustments, I will need to disassemble and slide out the board from its Faraday cage, then install a board or cable extender so it can be powered on and still accessible. The primary synthesizer board is the sixth bay from the left and the secondary board is the fifth. I'll need to start with the primary board and figure out how to make an extention board/cable for this thing. Any suggestions are certainly welcomed.Oh yeah, as a reminder to myself, I'll try re-seating the boards.

author: mag_therm
author_rank: Frequent Contributor
timestamp: December 17, 2021, 06:57:43 pm
content: The phase lock problem and construction and plug in modules with smc connectors on top are all somewhat similar to the Wavetek 3000 here.It is very difficult to diagnose a problem of non-phase lock, because all the PLLs get affected, impeded by the construction limiting access.I was able to make a harness with only the supply rails, and a Rg316 smc extender cable.That allowed to run modules one by one when opened up on the bench.The first failure here was a plastic op-amp in a PLL loop.The second was, fortunately just that a PLL capture point level drifted outside of the range, fixed by adjusting a pot.The modules were running above 50 C air temperature in summer so I put a small 12V fan to circulate air.

author: whirligig
author_rank: Contributor
timestamp: December 19, 2021, 03:02:05 am
content: Quote from: mag_therm on December 17, 2021, 06:57:43 pmDid the second failure affected certain frequencies?

author: whirligig
author_rank: Contributor
timestamp: December 19, 2021, 03:29:49 am
content: I re-seated the boards but the problem is still there. So I need to study up on PLL in general and press on.The photo below is a closeup of a disconnected SMB connector. I am having a hard time figuring out where to find these. I plan to buy a couple of these connectors to make an extension coax.Ooops, I figured it out. I thought these connectors were threaded and had to be removed with a small wrench. After pulling on one, it disconnected just fine.While examining the two synthesizer boards I found two cracked capacitors. The one below on the Synthesizer #1, C204 is described as a MKT, 0.47/63/10, R:4.5*9*7.2 RM2,I assume it's a mylar 0.47uf at 63V. Is the number 10 the tolerance? The other is on Synthesizer board #2, C309 which is a 0.22/63/10, R:3.5*8*7.2, RM1.Just confirmed the numbers after R: are the dimensions. I will need to test these to see if they're really bad. Seems like a conincidence that the only light blue capacitors on these two boards are cracked from, I suspect, overheating.

author: George Edmonds
author_rank: Frequent Contributor
timestamp: December 19, 2021, 05:30:39 am
content: HiYou have a damaged/destroyed SMB connectotor.George G6HIG

author: picburner
author_rank: Frequent Contributor
timestamp: December 19, 2021, 09:09:01 am
content: The SMB connectors are pushed in and extracted by pulling, they do not have to be unscrewed.However the one unscrewed is the female connector, probably just screw it back on and it should be as good as new.Regarding the cracked capacitors: there are also inductances in that case, from the photos I can't see well, but check it.One way to ascertain this is the silkscreen printing on the pcb: Lxxx or Cxxx.

author: George Edmonds
author_rank: Frequent Contributor
timestamp: December 20, 2021, 12:41:24 am
content: SMB connectors are removed by pulling the sleve with the three anular rings towards the main body of the connector not by pulling the conector itself.George

author: whirligig
author_rank: Contributor
timestamp: December 20, 2021, 04:35:46 am
content: Quote from: George Edmonds on December 20, 2021, 12:41:24 amThanks George, it came apart much easier than I thought. I just have to give it a good yank. I can put away the wrenches now.Quote from: picburner on December 19, 2021, 09:09:01 amThe printing represent the components as a C309 and C204. I plan to check them with my LCR meter. I found a third capacitor of the same color and markings on another board and it's also cracked. I would hate to replace everyone of these light blue devils. Well, I'll see how they check out.I've ordered all the parts to make the extender board. Ooooh, it's more than I thought I would spend but I found a 100mm x 220mm PCB for DIN 41216 connectors from the UK. It should make it a lot easier to troubleshoot the synthesizer. I should have all the parts by early January.

author: whirligig
author_rank: Contributor
timestamp: January 03, 2022, 04:56:12 am
content: I've built a board extender thanks to a UK ebay seller and I'm making my first measurement of the Synthesizer #1 board. The instructions are attached with some photos of the measurements I made with my tinySA. The measurement is made with AC coupling using a 300 to 600pf cap between the tinySA input at the center pin and to TP201. The connection was made using a BNC cable with a pair of test leads at the other end. The 48 mhz PLL level is suppose to be at -3dBm. I get just about that but the tinySA is not grounded to the DUT. If I ground it, I get a lower level of -15dBm. How should the spectrum analyzer be hooked up to the DUT in this scenario?

author: kawal
author_rank: Frequent Contributor
timestamp: July 01, 2025, 06:11:38 pm
content: That Euro card will short some of the serial signals. Not a good idea to use it with the RE125.Better spin your own board.Look at the Bus used in the RE125 - only power lines are triple connected . The connectors used in the unit are DIN 41612 48 pin (3x16 pin)Maciej