Minolta Color Meter II Service manual? - Page 1
Forum section: electronics / repair

author: borjam
author_rank: Unknown
timestamp: May 30, 2025, 06:14:23 am
content: I got a Minolta Color Meter II in very good condition , although it displays a consistent color temperature error of about 200 K.I would like to calibrate it but so far I have found no information. Opening the main case reveals a trimmer which (after fiddling with it) turns out to be a voltage threshold adjustment for the meter to complain about "low battery". I was hoping it was some kind of "general offset" but it's not.I have yet to open the detachable cell case, which is said to have six trimmer potentiometers. Given that it has three color cells I imagine each of them will have a couple of trimmers, maybe one for offset and a second one for slope.Does anyone have an idea of there can I find a schematic / service manual for it?Although I don't have specialised equipment to calibrate it I plan to use a known color temperature source (a cinema halogen 3200 K fixture) to set a known measurement, and use a set of Rosco color correction filters (which specify mired and green/mag offsets) to make sure it responds consistently. Not an optimal way but given that the intended use of these meters is to choose one of those color correction filters it should be good enough.

author: borjam
author_rank: Unknown
timestamp: May 31, 2025, 10:57:48 am
content: So, it seems that there is no information anywhere, no matter how much I have searched.I decided to give it a try. The meter was consistently off by about 200 K more or less, so it looked like it would be possible.I lack any specialised laboratory tools to do this, but the purpose of these meters is to measure light color temperature and green/magenta balance in order to compare lighting fixtures and correct mismatches (either color temperature or green/magenta from flourescent lights).I used:- A known color temperature and G/M balance light (0): Dedolight DLH4 halogen fixture that has fixed 3200 and 3400 K presets.- A Rosco Cinegel sampler kit.Rosco is a one of the main manufacturers of lighting filters for motion picture and theatre. The Cinegel range includes color correction filters (for example, filters to lower color temperature from daylight 5500 K to tungsten 3200 K) and fluorescent light correction.The meter has three metering modes: CB, CC and K.- K mode measures color temperature.- CB mode shows color balance in mireds related to one of the three film color temperature presets (3200 K, 3400 K and 5500 K)- CC mode shows plus-green or magenta values.The first measurement I tried was the CC value. After taking a picture of the trimmers and assuming their adjustments would not be too critical, I tried each trimmer making rough changes (30 - 45 degrees) until I found that the bottom right trimmer (3) affects that. After suceeding setting it to zero I made a measurement placing a Rosco #3304 (Tough Plusgreen / Windowgreen) which is equivalent to CC30 Green, and voila! The meter read a value of 10 for CC.Second, I looked for a K adjustment. Turns out it was trimmer number 1. After correcting it I found out that at least it measured two known colour temperatures properly: 3200 K from the halogen lamp, and mired 130 for the 3200 K preset and a full CTB filter with a mired of 131.Repeating the CB (green/magenta) measurement I found that it was off, so the conclusion was that another trimmer affected it. Turns out it was trimmer 2, which in turn set the color temperature a bit off.After fiddling again iteratively with trimmers 1, 2 and 3 trying to minimise errors I think I kinda nailed it. CB, CC and K are mostly within specifications.The Rosco sampler is not a laboratory tool, but given that the main purpose of these meters is precisely to choose a filter from these samplers, well, it makes sense to use it as a guide.Quick note. Almost forgot. There is a trimmer at the back of the meter body which you can access by removing the filter values table plate. It sets a threshold voltage level for the "battery low" warning. Probably some bias voltage as well? I left it as it was after experimenting with kinda extreme values and finding out that almost fully clockwise gave me a "battery low" error.