Service required for HP 9160A Optical Card Reader

[quantalume]

Those are nice images! I always enjoy looking at quality, old boards with their gold-plated traces.

(01-05-2016 09:30 PM)Jurgen Keller Wrote:  So I think my next tasks are:

• Follow the wires so we know which connector pin corresponds to which PCB pin.
• Do some measurements. Suggestions and assistance highly appreciated.
• Buy replacements for the broken parts. Suggestions to determine the exact kind of these parts is welcome. Shall I open them to determine if they are resistors or inductors?
  

Please apologize my lack of electronic knowledge. I really appreciate your help, and I think it's really worth to try reviving this device.

I'm pretty sure that those components are inductors. I believe that position on the card edge (#2 from the right) is where the -15 volts power enters. If you look at the other (presumably not defective) board, you will see another similar inductor, also connected to position 2, the other end of which connects to the negative terminal of an electrolytic capacitor. What we have here is an LC filter to clean up any noise on the supply line (or keep noise from the device from affecting the supply line). The defective board has two inductors which presumably connect to the two adjacent capacitors (you can verify this by following the traces on the back side of the board). My guess is that there are two switching circuits, one of which is the motor driver, which utilize that supply voltage, and they wanted to keep them isolated from each other and the supply.

One of the first things to check would be those electrolytic capacitors. They should initially indicate a low ohm value when you connect the meter, which rises over time (seconds) as they charge. If the reading doesn't reach megohms after a short while, then they are likely bad. In fact, it's good practice to replace electrolytics that old even if they seem good. You should unsolder one end of the capacitors when checking them.

If the capacitors appear good, I would suspect that the motor is drawing too much current. You could apply a DC voltage to the motor from a power supply or battery and measure the current. Let's hope it's not the motor since they are likely impossible to find now, although you could probably rig up something else to mount in its place. I can't tell from the photos; does the rubber wheel spin against another wheel, or does it grip against that metal plate? If there is too much friction, the motor won't spin freely and will draw an excessive amount of current. Unfortunately, because of the gearing, you can't just turn the wheel to see how much friction there is. You could, however, remove the motor and check the current again with the wheel spinning freely.