so ive had this 897 for maybe 6 years now and it started doing this thing a few months back where mid-transmission it just drops power, like it'll be putting out a solid 50w and then suddenly dips to maybe 5 or 10w for a second then comes back up. sometimes it stays down and i have to key off and back on to get it to recover. happens on all bands but seems worse on 40m for whatever reason.

i already reseated all the internal connectors i could get to easily and reflowed a couple suspect joints on the PA board that looked a little dull, but no change. ALC meter looks normal during the drop — it's not like the ALC is clamping it down. SWR on the antenna is fine, checked it with the external meter and it's flat. temp doesnt seem to be an issue either, happens within a minute of keying up even when the radio is cold.

anyone dealt with this on an 897 specifically? i'm wondering if it's one of the driver transistors starting to go or maybe something in the low voltage supply rail. dont really want to send it to a service center if i can avoid it, i have a decent scope and a DMM and im comfortable poking around in there.

Had almost the exact same symptom on my old 857D which shares a lot of the same innards. Ended up being a cold joint on the driver stage, not the PA itself — the visible ones looked okay but there was one hiding under a shield that was cracked just enough to act up under RF. What I'd do is get the service manual (if you dont already have it, eham or the usual places) and trace the drive signal with the scope while it's acting up. If you can see the drive collapsing before the PA output drops, you're looking upstream of the finals.

also worth checking the 8v rail if memory serves — the 897 has a regulator that feeds the driver stage and those aren't immortal. might be worth just scoping the rails while you're keyed up and watching for any sag during the dropout. that would at least tell you if it's a power supply issue vs a component issue on the board itself.

this is gonna sound dumb but did you check the TX/RX relay? on some of the older yaesu gear those relays get flaky and cause all kinds of weird intermittent stuff that doesnt obviously look like a relay problem. i chased a ghost on an FT-100 for weeks and it was the antenna relay contacts getting dirty. just a thought, probably not your issue but worth 5 minutes to clean the contacts if you can get to them.