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RA82 spinup troubles

That transducer doesn't look common, but try Googling every number on it. It may still be made by the OEM. Otherwise, we will need to repair it, or adapt some other photointerrupter. I would likely try the repair.

We need to figure out which side is broken, the LED or the phototransistor. The LED may not be visible, because it may be infrared. To verify an IRLED is working, look at it through a digital camera. To see what I mean, look at a TV remote control IRLED through a camera while pushing some buttons.

Assuming he IRLED is fine, next test the phototransistor. If a bright flashlight shown on the window will not get it to conduct, then the detector is shot.

Once the broken half is known, we can plan to rebuild the assembly. I would likely, carefully drill out the back side of the offending piece, intending to insert a T1 size case LED or phototransistor from the appropriate side. If your phototransistor is dead, we may need to add a buffer transistor outside (depending on the robustness of the phototransistor we find.)

Before you drill anything, tell us which side of the sensor is broken.

Lou
 
This will take some planning as there are various interlocks that prevent the drive doing much with the HDA removed (which is needed to reach the part in question).
 
If the interrupter really is shot, (& it does look a bit special), it is possible to get both side-looking ir leds & phototransistors. Very often after the gunk around the wires comes off, the actual components will just slide out of the plastic casing. I've rebuilt "special" opto interrupters this way quite often. Of course if it's completely moulded you might have to do a more serious rebuild, but the slotted plastic assembly with the components in is readily available, just probably not on that particular mounting.
 
Since you have removed the transducer, test the devices out of circuit.

Using a 1.5V battery, connect - to ground (Pin 2) and + to the +led (Pin 1). Watch through your digital camera.

Using three 1.5V batteries in series (4.5V), connect - to ground (Pin 2) and + to +5V (Pin 3). Watch the tach pulse (Pin 4) on your scope as you shine or don't shine your flashlight on the phototransistor. (Of course, ground your scope probe to the Pin 2 ground connection also).

Let us know what you find.

Between Nige and I, it appears that you have some rebuilding advisors at your disposal. The toughest I ever did was the BOT/EOT leader sensors in my dec TU60. They use incandescent lamps instead of LEDs that were potted into the assembly. I am very sure I have suitable LEDs and phototransistors around here when the time comes for yours.

Lou

PS. Also, I should admit that only now did I take a closer look at the transducer connection diagram that you posted earlier. The LED is shown, and the phototransistor is shown driving one other transistor, not driving a Darlington pair. I just wanted to correct that.
 
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Oh great. I think we have bigger problems. :(

I checked the IR LED under a nightshot camcorder.
DSC00014.jpg

Well, that was okay. Could it be the phototransistor?
To test: Put piece of paper in the way of the LED and see if the scope responds.
Result: Nope. It's not the phototransistor.

:confused:
What the hell? I checked it earlier and it wasn't doing anything.
Okay, lets put it back together and see what it does.

http://www.youtube.com/watch?v=UR7U9k6oBo8

Good news: I can totally rule out the transducer as being faulty as it seems to be working both while being tested and while in service.
Bad news: My problem is someplace else. :evil:

The FRU reference list int he service manual states an error code 01 could indicate a faulty motor/brake assembly, belt, servo module, or power supply...and I juat realized that errors 02-04 (all pertaining to speed) state a bad transducer.
I beleive I can rule out the power supply as it's rail LEDS are all lit, I'm quite sure the belt is not slipping or broken but the motor or brake, I'm not sure about.

Edit: While Iw as waiting for that video to upload, I went and found a piece of tube that I could pull the bulbs out with (who knew that a *cough*tobacco smoking device*cough* would serve suck a purpose) and suprise, ALL but the fault lamp bulbs are burnt out.
I'm going to have to wait until the weekend to buy replacement bulb, then try again and see what happens and if the REAL fault code shows its ugly face.
 
OK, now we've to to keep looking downstream. We have to get the RA82 printe set and start looking at the next active component that the phototransistor signal goes to on the circuit board on top of the HDA. At least the transducer works.

This evening after work I will look at the RA82 FMPS (field maint. print set.) and examine the downstream logic. I just downloaded the prints. The board on top of the HDA is called the read/write board and is about 90% toward the back of the print set. I'm going to have to take some time to digest it.

Lou
 
I have reviewed the prints. The tach pulse output from the transducer passes through the read-write (HDA top) board largely unaffected. The only component on that board is a 470 ohm pull up resistor (pretty strong for a pull-up). Then, the signal (called "tach pulse L") travels to the big board (called the Hybrid in the prints). It is inverted there in IC E12 (pin 9 in, pin 8 out), then leaves as "tach pulse H" the hybrid board to go to the servo board. On the servo board, the "tach pulse H" signal goes to and ends at E8 pin 36. That's it, it doesn't go anywhere else!

You can find E8 on this sheet that I have copied for you: http://www.vintage-computer.com/vcforum/attachment.php?attachmentid=5198&d=1297390107

I assume you know the order of pins on dips and can find pin 36. Scope it during spinup and see if the signal is there. If not, go back to the hybrid board, and scope E12 pin 9 and 8, looking for the signal. If it's present on 9 and not on 8, then E12 could be bad. It's a 74LS14 which is dead common. OR....

Something else is gong through my mind. When you were showing the phototransistor output pulse train in the video, what was the peak to peak voltage? The swing should be at least 4V or so, from 0V to at least 4V. Basically, I am concerned that the peaks really be high enough / lows really be low enough to toggle that 74LS14 I mentioned above.

I suggest you download the print set yourself and follow the tach pulse signal yourself to make sure I didn't miss something.

Lou
 
I don't yet know how to properly set the scales on the scope properly yet. The manual that came with my scope strangely is for another model. :/
I noticed that as well that the phototransistor was not either on or off. It could be variable which again might point to a weaker than normal IR LED.
The resistor was VERY easy to find. It's about two inches away fromt he connector on the right.
Thanks for the help there. I'll poke around that as soon as I can and see what comes up. I have one mental image in my head right but I'm not going to jinx it.
 
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I just watched the video two more times. When you had the transducer dis-mounted from the HDA, the pulse height on the scope was two divisions, and the trace would go up from the center of the screen. In the part of the video when you put the transducer back on the HDA, the pulses in the trace would drop down one division from the center of the screen. Did you press the invert button and change the vertical amplifier on the scope between the two portions of the video?

I have no idea what model scope you have there. But, the big knob though is the timebase that sets the horizontal sweep rate. There should also be vertical amplifier knobs for each input channel that set the vertical scaling.

Lou
 
I was mucking with the settings yes. The scope itself is a Sony/Tektronix 335. Nice $10 find if I do say so.
I probably won't be able to work ont he drive again until Sunday at the soonest.
 
Okay. I double checked and it seems that initially the transducer will let out .1v.
If the gap between the phototransistor and the LED is blocked, it will go to +5V.
So yes, the scope somehow got inverted by accident.

Would you be able to supply the sheet showing where E12 is? I can't find alphanumerical markings along the sides of the board.

Edit: Oh,that was unexpected.
After double checking my scope settings by manually triggering the phototransistor and reinstalling the transducer assembly, I powered up the system and did another spin up with my scope set and...off she went.

Edit: Hurrah! Ran a full diagnostics and not a single fault was found. Looks like I just have a cold joint.
Looks like all I ahve to do now to finish it off is complete the new cables and replace all the front panel bulbs.
 
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Yes, most excellent. It is funny how unplugging and replugging things a few times can make it all better. Sometimes the crud just has to be scraped off.

You might as well make one more video of the full spinup so that the viewers at home can hear that monster at full throttle!

Now you have some fine bench time ahead of you as you make those cables. I can take more (and closeup) pictures if you want.

Lou
 
*SNIPPITY SNIP*

Hmm. It appears that the tennants downstairs are not impressed with this drive. Spin it up at 8:15 at night (all noise must stop at 11 according to the landlord) and they start beating down the walls in a wordless method of saying "Shut the hell up".
Looks like the RA82 work and all work associated with the PDP-11/84 has hust come to a screeching halt in the form of a call from the landlord. :(
Guess this thing's rattling every corner of the house.
 
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Slightly o/t but we used to use a heavy rubber mat made from recycled car tyres and about 3/4 inch thick in soft play areas for sound deadening. I used offcuts on the stairs at my ex's house and it was quite remarkably good at silencing teenagers in army boots at 3AM. Perhaps you could get hold of some & rest the drive on that.
Failing that, a sandwich of thick foam & plywood would probably cut most of the transmitted vibration.
 
BuMP.

It's in the rack and I really want to finish this off.
Since the last time I have moved and gotten hold of a logic probe so I have been using that instead of the scope. I'm still having the erratic issues with the transducer where sometimes it will work but more often it does not. I would like to replace it however I don't know if it's a DEC specific part.

File16.jpg

100_2893.jpg


The only markings on it are

Code:
(HEI)  LGO7-CD
L10423   Rev C
 
I have. It works but it does not. As seen from youtube videos I made it's very hit and miss. Sometimes it will work perfectly, other times it won't. I can tear the drive apart to take it out and test it and it will work but put it back together and it's no good again. Yes the cabling between is good.
 
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