Manual for Macbeth TD-904 Densitometer

Threads on this topic are several and they are all quite dated so I dare to start a new one.

I'm looking for a manual for a TD-904 densitometer. They have been offered on this forum but many years back when this was still apug.org.
If anyone could help with a download or attachment via mail I would be grateful.

Thanks in advance!

Stefan

I'm asking because I bougth one at that auction site and the fan blows, the incandescent lamp fires up, the buttons on the right react when pushed but all I get shown by the display is:
"+1 . 1" and this doesn't change a bit when pushing any buttons. Am falling victim to my own stupidity or is it broken?

I found the manual online, but I still have no clue what is going on here.

For the record: https://www.johnesimmons.com/Graflex/MacBethDensitometer/MacbethDensitometers.pdf

Hi, the usual way to calibrate a unit like this starts like so: hold the probe head down, and while holding it down, momentarily press the zero button. (You do this with nothing in the aperture; no film.) The display should then read 0.00, or similar. Then you let the probe head back up; the reading should remain on the display.

What happens if you do this (with any color selected)?

If this was successful then the second part of the calibration requires a "check plaque" or whatever they call it. (This is essentially a piece of film with a known density value, perhaps somewhere around 1.50 or 2.00 or whatever.) You would act as though you are reading this, holding the probe head down. If the reading is correct (matches the check plaque value) then it's OK. If the reading is too high or too low then you adjust it with a small knob on the back of the instrument (while holding the probe down).

If things seem to be working, here are the fine points... you need to zero each color individually. But only adjust the back knob, essentially a "slope" adjustment, for one of the colors.

What is it that you're using, that you're trying to measure?

Many thanks so far for your kind help! I have been using a TD-502 in the past quite extensively which worked very well and reliably and is dearly missed right now. In my book: analogue technology wins once again!
The general usage is not a secret to me but the digital interface makes it less intuitive. The device did not come with a calibration-target but as calibrated Stouffer-targets are still availble, I can work around this.
I will try the above sequence and see if it changes anything, though, I think I already did. Just pushing down the probe and zeroing it didn't work afair: The device always displays what you can see in the picture above.
I'm away from home right now (with tripod and 6x7-camera in the trunk) but will check again and report when I'm ´back.

skahde said:

I will try the above sequence and see if it changes anything, though, I think I already did. Just pushing down the probe and zeroing it didn't work afair: The device always displays what you can see in the picture above.

Click to expand...

As I recall the zero function has generally been pretty reliable on Macbeth densitometers with respect to showing 0.00 in the display. So if it doesn't happen this suggests that perhaps the function is not being called.

If you can get access it might be worth having a look at the zero switch itself. Also the switch in the probe head. As I recall you should hear a faint "click" when the head is nearly full-down (If this switch doesn't activate then the zero function won't either, i don't think). Might be worth trying to operate the switches a couple hundred times with power off, just to see; maybe it will break through possible oxidation on the switch contacts.

I know there are forum members who have done repair work on Macbeth machines of this era; they might have something to say about the switches. Anything beyond this, I'm not much help. Other than to suggest a service manual.

Best of luck with your machine.