Icom IC745 display issue SOLVED - Page 1
Forum section: electronics / rf-microwave

author: s-petersen
author_rank: Contributor
timestamp: August 04, 2025, 03:03:36 am
content: I recently bought an Icom IC745 for parts / repair, and I'm having an issue, the VFD is nice and bright, but after 5-10 minutes it dims, and goes dead until I turn the radio off a few minutes and turn it back on. There is a second issue that is related, the RF gain, squelch, and signal meter are also having issues, the RF gain does nothing, and squelch also does nothing. The signal is at S9 and does not change, unless you switch it to FM, which is not installed, then it is zero. The reason I know it is all related is, when I swapped it into another IC-745 with a dim supply, the issues followed the display. I have replaced the 47uf caps in the display, but not the 6v one, because I need to order it. Does anyone know if there are caps in the display RF shielded box?Any insight would be appreciated.Thanks,Scott

author: KD4PBS
author_rank: Contributor
timestamp: August 05, 2025, 03:01:40 pm
content: Maybe it's two issues? You say on the first one that the display eventually gets dim, but when you swap that display into a second unit with a bad supply, it still doesn't work? Perhaps fix the supply on the second unit and see if that clears stuff up. Maybe the first unit has a bad supply as well?

author: s-petersen
author_rank: Contributor
timestamp: August 05, 2025, 03:45:43 pm
content: The problem is all of the issues travel with the VFD display, the radio with the dim display, always works correctly. At first, I thought some issue with the matrix board, but switching the display moved the other seemingly unrelated issues to the radio with the bright display. Does anyone know if the display unit is necessary for the operation of the s meter?, I was thinking of unplugging the display, and see if the s meter returns to normal

author: KD4PBS
author_rank: Contributor
timestamp: August 05, 2025, 06:50:26 pm
content: Now I'm confused.The write that the second radio has issues with the supply.Fix that and then you can verify if the issue follows the display or if the supply in the second radio is what's causing more issues.

author: s-petersen
author_rank: Contributor
timestamp: August 05, 2025, 07:48:27 pm
content: The second radio only had issues with a likely worn out VFD display, upon swapping the bright supply, it is also bright in the second radio, with the dim display otherwise working in the first radio, but the meter and squelch issues moving with the bright display to the previously working second radio. I am wondering what the display has to do with the s meter, and squelch?

author: KD4PBS
author_rank: Contributor
timestamp: August 06, 2025, 04:38:08 pm
content: My confusion is based on the initial report that the second radio has a supply issue which is apparently now being said is not the case at all. Sorry.Sounds like you've definitively verified through the process of elimination that the display has something to do with the S-meter.Time to break out the schematic and see where and how.

author: s-petersen
author_rank: Contributor
timestamp: August 06, 2025, 06:05:23 pm
content: I know.... time to dig into it, I was just hoping someone has already ran into this.. I saw a post a while ago, but it was unresolved, the inverter transformer was shorted, and the display completely died, and had the same symptoms with the s-meter and squelch, but it ended there. I am going to unplug the display, and see if the s-meter works properly, as in there is too much draw from the display, or that it still does not function, in that the display supplies something to the s-meter that is missing. Thanks for trying to help!

author: s-petersen
author_rank: Contributor
timestamp: August 25, 2025, 12:13:04 am
content: Solved... The display provides -5v to some parts of the transceiver, it's part of the inverter for the display. Without the -5v the meter does not work correctly, and also the squelch does not work and the RF gain as well.I removed the display, checked it, and a 1000mfd@6.3v cap was shorted., awaiting a replacement.