I picked up a 147 and 148. Feb 1978 markings on the original battery of the 147.
Opened up, clean inside, no obvious issues. Felt worthy to give it some line voltage w/ the thermal cam handy. Left the batteries hooked up, because kinda curious how 42 year-old batteries would respond. Set to "millivolt", "100" range, and turned zero suppress all off, (not that it should matter).
Got a buzz and some needle movement. No lights on the "AC connected" lamp (ds201) or "battery charging" lamp (ds202). Same issue on both the 147 and 148. (sidenote: based on the manual, whenever the 147 is connected to AC with the switch in the "off position", the battery will charge if necessary.) Buzz is coming from the mechanical chopper at the input.
Decided to start fixing the 147 first. Disconnected the now bulging battery, ha. After being on for 10 seconds or so, w/ the thermal cam I see large temp difference on the "PC-74" card, one of 2 upside-down plug-in cards, which seems to be the home of power supply circuits. While the rest of the internals are at room temp more or less, R232 on PC-74 is quickly ~150F (top cover is dark in that area too, same as Dieter). Taking the board out, Q27, a 2N1535, is also quite hot (to-41, germanium PNP).
More to come. Also, while looking around found some leaky electrolytics on the other plug-in card, PC-75, which is the 94Hz oscillator. I changed them, but I don't think they were the source of any particular problem. Out of circuit they tested pretty well, age considered, including leakage current. If anyone's interested in that data, I'll post below.
Cap data:
Sprague "Verti-lytic" original caps;
replaced C304, C306, and C307 (15v 100uF), C305: (15v 10uF).
C304: 11V for 7.5 minutes, leakage of 995nA. @100Hz 126uF, ESR: 0.5R, tan: -87.5 deg. Replaced with Nippon KZE 50V 100uF (on hand, leakage was 200nA for comparison).
C305: 11V for 7.5 minutes, leakage of 1.9uA. @100Hz 11.4uF, ESR: 4.1R, tan: -88.2 deg. Replaced with a Nippon BT 25V 10uF (leakage 42 nA).