[R-390] Help with R-391 needed

[g4gjl at btopenworld.com]

Season's Greetings to all !
This is an HT fault and though its on my R-391, I think the R-390 knowledge would be equally helpful in diagnosing, as I believe the R-391 electrical differences from the R-390 lie purely in the low voltage circuits..

I'm after some assistance in diagnosing the following fault, before I rip the R-391 wiring loom to pieces :o(
The initial fault was 'no receive'. After some early diagnosis I noticed that all four 47-ohm ballasts in the rectifier deck had burned out. These I replaced with Wirewound 4-watt units. On re-test the RX does not build up HT, and I can sense a heavy load on the power transformer as the rectifiers and regulator tubes warm up.
After extensive probing with the AVO ohmmeter, I found the following:

I have isolated a +180vdc fault to the mainframe.
The following internal plugs are DISCONNECTED:RF Deck
PTOXTAL sub chassisCalibratorIF stripAudio deck (J319)PSU/transformer (actually irrelevant)
Furthermore, I have unsoldered the HT smoothing cap, C103 positive connection, to eliminate this capacitor from the test..

Measuring with the ohm-meter from the audio deck test point to ground I get a 10.5 ohm resistance. (only when J620 is in place) The 10.5 ohm reading disappears if the audio deck plug, J620 is pulled.
I can measure the 10.5 ohm resistance on the loom side P120-3  There are no other low resistance measurements on either the loom side P120-6, P120-7, J620-6 or J620-7: these are all high.
So it looks like there is both a short and a break somewhere in the HT wiring of the   mainframe loom.
I have two questions, therefore:Q1.  Are there any other capacitors on the HT+ rail, hidden away on the mainframe, which are not shown in the manual? (I am using TM11-863) Q2. Are there any well known pinch points in the mainframe loom that I should focus on initially?
 Note that C101 is irrelevant here as it is upstream on the regulator tubes.
Your help appreciated.
Pete WorrallG4GJL