Around December 1970 Thorn introduced the thick film unit for the video module. There were still holes left on the PCB for the old style resistors should it be required to revert back to the original. I have heard the thick film was introduced solely for the 3500 and that over times as the 3000/3500 modules were interchangeable that’s how they ended up in some 3000’s, that is not the case. The Thick film was announced in the BRC Bulletin of Dec 1970 as below.
These film units were not the most reliable of components, Thorn certainly liked to use them more and more, the 9000 seeing them used much more but not to the extent that they were used in the 4000 and hence it having a poor reputation (whilst we’re on about the 4000, I would like one so if you have one please get in touch). Anyway back to the 3000/3500 thick film used on the video panel, the end product of this component aging and failing, was intermittent Grey-Scale drift and in some cases all red, green or Blue pictures.
In an effort to improve reliability it is recommended that you remove these units and revert back to the earlier configuration which employed six individual resistors, three 12K 7W and three 56K 1W.
These are as resistors are as follows:-
R259, R264 & R277 (12K)
R249, R263 & R276 (56K)
Its a very simple job, takes no more than 10-15mins to do, the stability rewards are well worth the time. I would add that I have kept one set with the thick film unit installed. Luckily I have a number of NOS ( new old stock units), I did this so as to have at least one working example to document the life-cycle the 3000 went through.
Below are some pictures of a panel with the thick film unit and how it looked after it was replaced.