Just took a quick glance at the print and it shows D800 as a 1N4007 (I know you already know this but I'm not totally up to speed here with all your tinkering) which is not a zener. It appears to just drop. the voltage by Its forward voltage. which is what, .7v?
So, I would install a 1n4007, ignore the partslist calling it a zener, and expect to see 8v on the supply side (anode) and about 7.3v on the load side (cathode).
Regarding zeners, (which I don't think d800 is) It's not best to think in terms of ohms imo.
Its better to think in terms of voltage and current.
But as you know, a zener will conduct/ let current flow backwards depending on the voltage. I don't know the voltage your Dvm applies across its leads in Ω setting, but obviously that would be a factor.
Thanks for the reply, Tha fios agaibh, VERY INTERESTING INDEED! this is going to be a l o n g reply as it contains a fundamental ERROR I have made. I looked at the diode's symbol Cct.Diag. and thought A-Ha! not a Zener! - but a Diode 1N4007. Q: why do they say it IS a Zener in the Parts List I wonder? (answer:
look more carefully at the Parts List!) Now I have my 20 (Qty) 5.1V Zener diodes, BZX79C5V1 500mW (only cost £2.22 GBP) I can compare the look of them to the original which I removed - and they look identical. Not a Black cylinder with a Grey band at one end, but a translucent, much smaller, component made of some glass-like substance. Just as well I got 20 as one has just fallen on the floor and I cannot find it! Back to the main issue: identifying this component. I noticed, of course, there's an identically symbolled diode in the Cct.Diag. for the A-7V. rail right next to our diode leading from CP14 pins 16&17. I am looking for this right now. In the mean-time, looking at the identification marks on the AUDIO_VIDEO_PCB (right underneath the Zener itself, so you may not see it without removing the Zener) it is shown as a Zener Diode - with the Z bar as you described. I think it must therefore BE a Zener - like in the Parts List. and not an IN4007 as shown on the Cct.Diag. Also, of course, the symbol on the AV_PCB shows the way round that Zener should be installed with the 'Z' Cathode . . . WAIT a moment! There's another D800 on the PCB. and this is a Diode proper. It is ranged along-side D801 at the end of the Tuner/Antenna can, and between two Electrolytic Caps. Nos.C808 & C811. What
have I done? Back to the Parts List (page 185) There's only one ZD800. That's the one I removed - so I must re-install it (with a new one) according to the printed symbol on the PCB. I must look at the Cct.Dig. to see just what I have done here! Mea Culpa Maxima! Then I must check this new-found D800 - which is described on the Parts List as 'D,SWITCHING 1N4007'. So, according to the Data Sheet from:-
ON Semiconductor, the 1N4007 has the following characteristics:-
Peak Repetitive Reverse Voltage: 1000V..
Non-Repetitive Peak Reverse Voltage: 1200V.
RMS Reverse Voltage: 700V.
Average Rectified Forward Current: 1A.
Vf = Typ. 0.93V. Max. 1.1V
Vf(AV) Max. 0.8V.
Testing the D800:
Applying the DVM in Diode Mode across D800 (the real D800 this time!)
DVM (-) to Anode, (+) to Cathode = 0 reading
DVM (+) to Anode (-) to Cathode = 0.621V.
Michael Studio1 UK 11:53GMT