Quantum Calculite XP circuit repair

<p>The Quantum Calculite XP light meter I bought off e-bay a while back does not give correct readings, although it is not erratic in it's readings - it will respond consistently to a given light intensity. So I decided to have it calibrated by Quantum. This is the reply they sent me:</p>

<p><i>The CPU which is a custom integrated circuit and was solely programmed by us is defective and is no longer available.<br /><br />Due to the proprietary circuits used I do not have any suggestions on how to have it repaired by anyone <br />outside of Quantum.<br /><br />My suggestion would be to try to find a working used one through the Internet. As you know, anyone with a <br />meter of this caliber will not part with it easily.</i></p>

<p>Some of you may know that the Quantum Calculite XP was noted as an exceptionally good meter in low light - it's sensitivity of -7EV goes far beyond anything currently manufactured. For that reason alone I don't want to give up on this thing quite yet. Anyone got any ideas about how to repair this meter? As I said above, it reacts consistently to light - but varies upto + / -1.5 stops compared to my Sekonic L 558, across a range of light intensities.<br>

Any advice much appreciated.</p>

<p>If you can't find another consider the Gossen luna pro SBC. I bought one for night time work for around $70 in mint condition. Realisticly the sbc measures down to -8ev. The dial centers 0 on -5ev but the needle can still display another 3 stops below that! I'm doing it now as I scan my studio. The are quite common too .</p>

Nathaniel - I knew the Gossen was good - but I didn't realize it was that good. Thanks for the suggestion.<br>

Best,</p>

<p>Gerard</p>

<p>I'm wondering if anybody has any ideas about repair of the above mentioned meter - or if that's out of the question.</p>

<p>Quantum informed you that repairing the meter requires a part that is no longer made: "<em>The CPU which is a custom integrated circuit and was solely programmed by us is defective and is no longer available." </em> One possibilty is to obtain the part from another meter that is defective in another way. Another unlikely possibility is to find an independent repair shop that has the part on their shelf, but my impression is that most photo repair places send meters to the manufacturer and so are unlikely to have parts. It would be easier to find another meter that is working.<em><br /> </em></p>

<p>The Calculite uses a standard IR filtered silicon diode sensor, which must have some "off the shelf" variation in output from sample to sample, so I would be very surprised if Quantum had made no way of easily adjusting the meter to compensate for diode variations.</p>

<p>While it would be possible to test every individual diode and program the chip appropriately, this would hardly be a realistic way to go about things. Therefore I'd be very surprised if there was no simple adjustment potentiometer or resistor in the circuit.</p>

<p>I'm not curious enough to take my own Calculite apart to test this theory, but if you can find an easy way into the casing, it would be worth a quick peek before consigning the meter to the scrap bin. Perhaps the diode itself has gone low output or something similar? Or maybe there's just a dry joint in the circuit? Not to contradict what Quantum have told you, but good electronic repair diagnosticians are a rarity these days.</p>

<p>My experience with programmable CPU chips is limited, but it's my understanding that some early types can "grow back" the programmable fuses which are blown during the programming operation. This can sometimes be put right by re-programming with the original data. This of course would be a completely foreign concept to the modern "repair" department staffed by board-swappers.</p>

<p>Michael, Rodeo Joe,<br>

Thanks for your advice. As I explained above, I own other meters for general use - the calculite is for low light, and I don't think there's any true substitute. They are very difficult to find, as other posts on Photo.net have proved - so the likelihood of finding a second broken one and swapping parts seems slim. Rodeo Joe - thanks for your guidance - I don't know much about the inner workings, but I will try to find somebody who might be able to take your advice and do something with the meter for me. I really find it hard to believe it can't be calibrated.</p>

<p>There are three luns pro sbc's going on the bay uk at the moment. very reasonable</p>

<p>Nathaniel,</p>

<p>I'll look into it - thanks. I think when I originally researched the Calculite, it's specs. were Min. Lux. of -7EV. Most modern meters are -2EV, and the Luna Pro SBC was -4EV if I remember correctly. As you say above, the Gossen might be able to go lower, and even if it can't, for the right price it's better then anything else around. So I will check it out. </p>

<p>Thanks</p>