Component Identification

[J.BO]

Hello,
I fix Intra-Oral Sensors (Dental Sensors) at my company and I need a little help. I've troubleshot a common failure to a specific component on a sensor head. It's a MSOP-8 IC. No number, only three letters on the top "HMA". The only other marking is a triangle which I believe is the logo for the company Analog Devices. This component is what allows a sensor to accept radiation from a tube head. Essentially, radiation is sent through a scintillator, some crystals, photo diodes (which gets converted into current), then this chip does something else. At first I thought it was an opto-coupler, but Analog Devices does not make an opto-coupler from what I've seen. This MSOP-8 package, along with the dimensional measurements I took from it, are consistent with their Op Amps. However, when I take voltages from this chip off a working sensor head, I'm getting less than 1 volt off every leg I measure. I'm not sure this is consistent with an Op Amp. My other thought was it might be a switch. Anyone have any thoughts on this? Thank you in advance for any help anyone can give. FYI, if anyone is familiar with these sensors, the specific one I'm referring to is a Kodak 6100.

 

[rjenkinsgb]

I'd guess it's a dual op-amp of some sort, to amplify or buffer the output from the photodiode detector.

If that's the case, I'd expect the power supply to connect to pin 4 (top right) negative and pin 8 (bottom left) positive.

Some CMOS opamps can work from very low supplies.

What voltage to you get between pins 4 and 8, or 4 and 7 (the usual supply pins for single opamp)?

 

[J.BO]

rjenkinsgb,
Thank you for the reply and info. As soon as I get another good working sensor, I'll check the voltage across those pins. I just checked voltages individually off each leg referencing off of one grounding point.

 

[J.BO]

rjenkinsgb,
Between pins 4 & 8 I'm getting 185mV. Between 4 & 7 is 0V.

 

[rjenkinsgb]

Strange!

From a quick search, it appears Analog Devices use a different combination of power pins on some instrumentation amps.
Try between 5 and 8 (or 1 and 4, in case it's the other way around than I thought)?

 

[J.BO]

rjenkinsgb,
Between 5 & 8 I'm getting 57mV. Between 1 & 4 I'm getting 102.7mV. The most voltage I get in any pin combo is .9V between 3 & 6. This does not seem like Op Amp numbers to me.

 

[rjenkinsgb]

It does not make much sense for anything!

Are you sure your meter is OK?

 

[throbscottle]

The letters HMA seem to indicate it's an AD8132 from Analog Devices, which is a differential amp. So, if this is the case:
pin 1: in-
pin 2: vocm
pin 3: power, V+
pin 4: +out
pin 5: -out
pin 6: power, V-
pin 7: no connection
pin 8: in+

Power supply range is +2.7v to +/- 5.5v

That "PCB" is a thick film circuit, the large grey rectangles are resistors, the little boxes above the chip are capacitors.

It's looking much more likely that the power supply for the unit has failed, or something in series with it being open or across it being short, rather than the chip.

 

[J.BO]

Thank you all for the replies. I've tried multiple chips (dual op amps and switches) to no avail. I started a new search and also came across the AD8132 and the 8131. I'm basing these choices off the fact that pin 7 is NC which matches the circuit. On a good chip, the highest reading I get is .9mV. I'm wondering if this thing doesn't work until the sensor is hit with radiation? If that's the case, it would explain my readings. Thanks again!

 

[throbscottle]

If you are only getting 0.9v between the power pins, the chip is not getting any power. Check the PSU and cables.

 

[J.BO]

This chip is in fact a Differential Op-Amp (AD8132). In this particular application, it won't actually turn on until it's hit with radiation. Just thought I'd share the results. Thanks for the help!