Post Reply 
Service required for HP 9160A Optical Card Reader
01-04-2016, 11:32 PM (This post was last modified: 01-04-2016 11:34 PM by jebem.)
Post: #10
RE: Service required for HP 9160A Optical Card Reader
(01-04-2016 10:21 PM)Jurgen Keller Wrote:  No, I haven't found yet a circuit diagram for the OCR.

I have inspected the connector and the device. The connector is clean, no crud. No lose or frayed wires as far as I can see. However, I found a resistor that looks damaged, see this picture (it's the small one in the middle with a crack). Probably that's not the root cause, just the consequence of another defect. Anyway, it's a starting point.

In addition to what TASP has mentioned:

If you are able to measure Zero Ohms between the power supply pins, it should be kind of easy to find the failed component thanks to the vintage easy to work with PCB.
While a schematic is always useful, for these kind of vintage equipment where we can clearly see the discrete components and read its references and values, it is like your schematic is the PCB itself.

I assume you are using a digital auto-range multimeter. If not, select the lowest resistance scale you can get from your equipment.

Is the reading resistance value steady at "zero" ohms?
Connect the multimeter probes and wait a few seconds. Did the value change?
Reverse the probe leads and repeat the reading. Is it the same?

The reason for this test is simple:
1) Depending on the multimeter type, a "0Kohm" value is normal when a large capacitor in parallel with the power supply lines is discharged - it will start charging from your multimeter and it will take a few seconds before you see the resistance reading start to increase.
2) Semiconductors shows resistance variance (even after failure) dependimg on polarity.

Assuming the zero ohm (or close to zero) is a steady value, then it is time to do a visual inspection and follow the copper traces to find what components are in parallel with the power supply lines.
Usual suspects are: capacitors, diodes, voltage regulators, and semiconductors in general.

In fact, a probable candidate is a voltage regulator IC (integrated circuit) that will have two of its legs connected in parallel with the power supply lines, so it is very easy to spot it.

It can be just a simple 3-leg component (like the TO-220 79nn or 78nn series, or maybe a TO-3 case). These IC regulators can have catastrophic failure and the result is what you are experiencing on that 9160A.

Usual technique to test those components: Use a cutter to remove it from the PCB (or use a soldering iron and a desoldering tool to keep the component leads intact) and test it out of the circuit. If the component is good, solder it back.

You may post pictures showing all the PCB if you like. Maybe we can spot the suspect there.

Jose Mesquita
RadioMuseum.org member

Find all posts by this user
Quote this message in a reply
Post Reply 


Messages In This Thread
RE: Service required for HP 9160A Optical Card Reader - jebem - 01-04-2016 11:32 PM



User(s) browsing this thread: 1 Guest(s)