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docs/discovery-notes.md

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+# Discovery Notes
+
+This file records hands-on observations separately from manual-derived facts.
+Treat these as bench notes: useful and current, but still worth rechecking with
+photos, continuity tests, and instrument captures.
+
+## 2026-05-13 - RCP-TX7 10-Pin Power and Cable
+
+Observed on the RCP-TX7 10-pin remote connector/cable during restoration work:
+
+- Pin 9 confirmed as ground / DC return.
+- Pin 10 confirmed as power input.
+- Cable color for pin 9 / ground: brown.
+- Cable color for pin 10 / +12 V power: brown-white.
+- Cable colors for pins 1-8 have been continuity-mapped; see the working cable
+  map below.
+- Yellow and yellow-white conductors are present in the cable but did not map to
+  connector pins during continuity testing.
+- With power present on pins 9 and 10, the panel shows a green `PANEL ACTIVE`
+  light.
+- The inside of the 10-pin cable contains 12 wires total.
+- Three of those wire groups are twisted pairs.
+
+Immediate implications:
+
+- The bench result agrees with the RCP-TX7 and CCU-TX7 manual pinout for pins 9
+  and 10.
+- The 12-conductor cable construction suggests not every conductor maps
+  one-to-one to the 10 connector pins; shielding/drain, duplicated grounds, or
+  paired signal returns may be present.
+- The three twisted pairs are likely important candidates for serial data,
+  composite video, and/or power/ground pairing, but this should be confirmed by
+  continuity testing rather than color or twist assumptions.
+
+### Working Cable Map
+
+This table combines the manual-derived pin purpose with hands-on color mapping.
+Rows marked `confirmed` have been checked on the current cable/panel under test.
+
+| Pin | Purpose | Cable color | Status | Notes |
+| ---: | --- | --- | --- | --- |
+| 1 | Spare / unused | red | confirmed | No function shown in service manual. |
+| 2 | VBS / composite video X | black | confirmed | 1.0 Vp-p composite video input to RCP. |
+| 3 | VBS / composite video ground | green | confirmed | Video reference/ground. |
+| 4 | Serial data, RCP to CCU/camera | orange | confirmed | RS-232C-based data direction. |
+| 5 | Serial/data ground | blue | confirmed | One of two serial/data grounds. |
+| 6 | Serial/data ground | grey | confirmed | One of two serial/data grounds. |
+| 7 | Serial data, CCU/camera to RCP | purple | confirmed | RS-232C-based data direction. |
+| 8 | Spare / unused | purple-white | confirmed | No function shown in service manual. |
+| 9 | DC return / ground | brown | confirmed | Confirmed as ground on current cable. |
+| 10 | +12 V remote power input | brown-white | confirmed | Confirmed as power input on current cable. |
+
+### Unmapped Cable Conductors
+
+The cable contains two additional conductors that did not show continuity to
+the 10 connector pins during the current test:
+
+| Conductor color | Current status | Notes |
+| --- | --- | --- |
+| yellow | unmapped | May be shield/drain-related, spare, broken, or connected only at one end. |
+| yellow-white | unmapped | May be shield/drain-related, spare, broken, or connected only at one end. |
+
+Recheck these against connector shells, shield braid/drain, cable strain relief
+hardware, and both ends of the cable if accessible.
+
+Suggested next observations to capture:
+
+1. Connector orientation photo showing pin numbering reference.
+2. Wire color list, including which colors form each twisted pair.
+3. Confirm whether yellow and yellow-white connect to shield, shell, or one end
+   only.
+4. Resistance between pins 5, 6, and 9 with the cable disconnected.
+5. Scope/meter idle voltage on pins 4 and 7 relative to pins 5/6 and pin 9.