RA82 spinup troubles

[Lou - N2MIY]

When you look at the output of the phototransistor on the scope, what does the voltage look like? Does it have good strong changes in voltage level? I'm wondering if it's marginal when it's in either of the states, and perhaps the next gate downstream is not being satisfied (all the time anyway).

Lou

 

[NeXT]

Okay, so I set the harness on the bench and supplied +5v to +LED and +5V lines, attaches GND and connected TACH to my scope.
Obstructing the light path produces a really weak response. This might be because I'm abusing the AGC-AVC voltage controls on a signal generator and the LED along pulls the voltage down to 1.2v.

Anyways, if I leave TACH and +5 connected (so +LED and GND are not attached) and shine a flashlight at the sensor I get a good 3v high/low difference. Oddly, if I also attach GND the signal goes weak again. Sounds like it's shorting itself out or again the shady power supply is struggling.

It shows what I previously saw and that is the transducer works but if I install it, it won't. At this point I'm suspicious what would happen if I just snapped off the internal LED and replaced it with a white LED I have.

 

[Lou - N2MIY]

So, do you think the LED that's on the photointerrupter is an IR LED? (If your eye can't see it, that's likely the case.) If you have a CCD television camera, it might see the IRLED and you may be able to see flickering or intensity change that jives with your "sometimes it works, sometimes it doesn't" diagnosis.

As for replacement with a white LED, it might work since your flashlight saturates the phototransistor nicely.

Lou

 

[NeXT]

It's an IR LED. I use my Handycam's nightshot to see if it's behaving and it's constant. The sensor seems to react to about any source of light I focus on it.

 

[NeXT]

Success.

I noticed that the top and bottom of the transducer are glued in. After popping those off I noticed it isn't potted inside. I pried out the LED assembly which was a blob of epoxy on a PCB and then I referred to the schematics.

That's bad. I should be seeing the GND also go to the optical pickup on the other side but I wasn't seeing anything. Under a a good light however I saw that there was a super tiny wire that had broken.

There was enough wire left that I used some patch wire to repair the connection. It was delicate but it seemed to work.

The result however was VERY reassuring.

The drive now spins up and has reached READY, however all three times I have spun up so far it has either failed to reach ready because of a fault or aborted because of a fault. First one was a SERVO COARSE POSITIONING ERROR, then I got a successful spinup, followed by a SPIN ERROR, then the latest time was R/W COMMAND ERROR. The first two lay suspect to the servo board but the last one I hope is the result of just a poor ribbon cable connection somewhere because it scares the hell out of me. One thing I do for sure know however is that it can and WILL reach a normal working state and that between the last time I had it working and now the drive had been stored with both the heads locked and the belt tension released.

 

[NeXT]

So the problems didn't let up with a connector cleaning. Out came the VT-100 again.

Following the steps in the service manual the system appears to pass with flying colors in the spun down state. Spin the drive up now however...

Error C6 is a PLO error, following that the drive aborts spinup and gives error 26 which is the system indicating the drive speed has dropped 3420 RPM.
The front panel blinks the fault status for SPIN ERROR which states the fault is either on the servo module or CPU module. I retested the PLO circuitry from the diagnostics and it passes. :tellme:

Every so soften the exact errors change or appear or go away but it's always something on the servo board which in the past I have never had any issues with.

I'm running into way too many variables now. I'm just going to back off on this again until I can better troubleshoot this on paper.

 

[NeXT]

Still working on this.

So I finally am back in a position to retest having moved to a drier climate and cleaned the machine out. I replaced the bad fan to ease my worries about overheating however:
1: These fans are 120V
2: If you want to use a 12V fan you're going to need a 30 ohm resistor because there is no +12 ANYWHERE in the drive. The closest is +15.

Anyways I started back off with our friend the Spin Error. So I hung my logic probe off the harness. It didn't work.
Odd. It was fine up on the bench. Whats the voltage?
To my surprise the +5 on the R/W was VERY out of range. It was hanging at 1.3v in fact. I discovered that if I disconnected the positive on the phototransistor's LED the voltage would come right back up. It's somehow shorted itself I guess. This MIGHT explain some of my other errors as well if none of the logic on the R/W board was being properly driven. Anyways, I tore the transducer apart again, pulled the old LED out and hot glued in a new one. It's almost 1AM so I'll try putting the drive back together and testing it in the morning but on the bench I'm reliably seeing high/low peaks from the transducer again so we MIGHT finally have it in the bag and be able to move onwards to that hot motor....or that PLO error.

 

[NeXT]

Okay, so after a final checkout I can confirm the transducer is now REPAIRED.

Me being an idiot forgot that there was a resistor in series with the transducer's LED already. Oh well, if it was a problem before it's fixed now.

It's working and it's reliable.
HOWEVER something is keeping TACH high. This is why I'm getting spin errors.

Edited: I'm going to start over and figure out where the tach goes.
Following the pulse (I swear I did this before) the TACH PULSE L has a pull-up resistor to 5V, then travels to pin 16 on the cable to the Hybrid board. From there it Passes through a 74LS14 and becomes TACH PULSE H. This travels to pin 5 to the cable for the Servo board (this is the board that my PLO problems would surface from as well).
From there I lose track of it on the schematics. Can anyone else find it? I'm reading this PDF and the Servo board starts on page 125.

 

[NeXT]

Okay, lets try this again from square one, jesus christ.

I passed on my results on the circuit being stuck high with the resistor in the circuit and after looking at the schematic he says it's STILL the damn transducer as even with the resistor connected the phototransister in the assembly should still be able to pull the signal low when it isn't. The final decision was to completely replace it. I mentioned I couldn't find suitable replacements. He found them in about a minute. >_<
So this order is in the mail and we'll try again in a few weeks.

 

[RSX11M+]

You're not alone here... I've been watching with interest, but not much to contribute. Expect I'll be going through the same with mine eventually. BTW - Loved that emoticon.

 

[RSX11M+]

This is a bit of a monster to navigate without using the NETLIST. Damn... wish I could edit these PDFs.

Servo Control

• Netlist beings pdf-159
• Schematic = pdf-135 (sch-01) though pdf-158 (sch-24)
• BOM = pdf-129 thru pdf-134

Kind of blindly, I'll try to follow that TACH PULSE -H On the Servo Control BD

• pdf-134, sch_pg-01, (D5 ) = "J402-5"
• pdf-153, sch_pg-19, (C8 ) = "ROM 1 E8-36"

I think it might be of help to locate all the boards and sections in the schematic for you. At least you'll know where to go without having to search laboriously.

Would that help?

 

[NeXT]

New transducers arrived and was fitted to the old mounting block with a dremel and hot glue.

...But I'm doing something wrong. I HAVE TO BE and I don't know what it is.

For reference, here is the old transducer diagram.

(ignore the pin numbering on J501)

Now here is the diagram for the new one as well as the relevant circuit on the R/W board.

(refer to THIS for correct pin numbering)

I never found that extra transistor so I tried to replicate it with a 2N3904 with the collector being the TACH PULSE, the base being the output of the transducer and the emitter being ground. Didn't really make sense but whatever, so I set it up on a breadboard.

THIS DOES NOT WORK.
As observed on the old transducer TACH PULSE remains high at all times.

 

[RSX11M+]

This is one of those instances where a picture is worth more than 1000 words. Sorry I can't do a new schemo for you easily at the moment. That machine is in the midst of a week long disk diagnostic. If you post a new one before trying it, I'll check it.



I don't think an external transistor will be required. The output should be strong enough and in the same phase as the original. (If not, then we'll add one)

Referencing your schematic as it now is...

The opto-coupler should be connected as follows:

• Emitter to ground (J501-4 ?)
• Collector to TACH PULSE L and pull-up resistor R111 (470 ohm) (J501-7 ?)
• LED Anode to R113 (200 ohms would be better?) (J501-1 ?)
• LED Cathode to Ground (J501-2 ?)

36ma driving that LED: [82 ohms?] seems a little high to me. Is that in spec for the new device? If you don't want to modify the original board - add a 150 or 200 ohm resistor in series with the LED.

I was confused by the pin numbering so this description seemed clearer. If I understood correctly, you had collector and emitter transposed before - yes?


Testing: Hopefully - the wavelength characteristics of these devices are chosen so ordinary visible light doesn't pollute or swamp the detector. I'd check it out with light sources to be certain. This could be a cause of trouble when in situ as well.

 

[NeXT]

Emitter to ground (J501-4 ?)

Yes.

Collector to TACH PULSE L and pull-up resistor R111 (470 ohm) (J501-7 ?)

Uh-huh

LED Anode to R113 (200 ohms would be better?) (J501-1 ?)

I got a 220 so I'll swap that in. Ok.

LED Cathode to Ground (J501-2 ?)

(BTW, this arrangement does not seem to work (nothing attached to base?). The line is still high.)

36ma driving that LED: [82 ohms?] seems a little high to me. Is that in spec for the new device?

The original transducer used an 80 ohm resistor as well. Even though this is IR I can always check the output with a nightshot camera in case I've overdriven and burned the LED out.

 

[RSX11M+]

Saw you just replied - so I hope this catches you.

I'm having difficulty understanding which drawings are your proposals, from renditions of how the original was. [didn't look at a schematic yet]

Most cell phone cams are sensitive in IR - so you can use that too.

Having my other machine down is really killing me - this should be simple to sort out.

 

[RSX11M+]

...

(BTW, this arrangement does not seem to work (nothing attached to base?). The line is still high.)


The original transducer used an 80 ohm resistor as well. Even though this is IR I can always check the output with a nightshot camera in case I've overdriven and burned the LED out.

Yeah... we're talking apples and oranges here.

So from your comments you are including an external transistor in the mix.

In my comments, I have assumed we're talking only about the opto device in your second image.

So to be clear... I need to find schematic pages where J501 is pictured, and to understand what components were on the original sensor.

I now realize you're adding stuff externally that I assumed was on the board.

See my confusion?

UPDATE:

Read/Write module diagrams begin on PDF pg 169 to pg 181 with J501 on 179

I now see your partial schematic is taken from pg 179.

Were there components on the original cable assy?

 

[NeXT]

So to be clear... I need to find schematic pages where J501 is pictured, and to understand what components were on the original sensor.

Doesn't exist. I ran up the part numbers on the old sensor and never found any details, that snippit from the RA81 manual is the best there is and implies that in the one package is the IR LED, the phototransistor and an additional transistor. What you see on the breadboard was:
-The load resistor for the IR LED
-The pullup resistor for the TACH PULSE line
-The second transistor that was in the transducer

I never added anything new to the circuit. I'm just trying to make the connections with little knowledge on how it originally worked. If you want me to simplify it, just tell me.

See my confusion?

Is it bad if I say "not really"? :|

 

[RSX11M+]

There have been a few advances in optoelectronics in the past 30 years, so there should be no need for an external transistor.

If you want to breadboard it before installing that's ok. Your breadboard need only include a series resistor for the LED and a pull-up for the collector of the opto's output transistor.

Connections are in my post:

The opto-coupler should be connected as follows:

• Emitter to ground
• Collector is TACH PULSE L - to pull-up resistor (470 ohm)
• LED Anode to series resistor (standing in for R113)
• LED Cathode to Ground

For the actual device cable I expect this would be how to connect it to J501 - The opto-coupler should be connected as follows:

• Emitter to ground J501-4
• Collector to TACH PULSE L J501-7
• LED Anode to J501-1
• LED Cathode to Ground J501-2

As I said - 36ma is too much current for a modern LED. I'd try to size the dropping resistor to 10ma at most, unless the specs for the opto device state otherwise. (LED's usually drop 2v - leaving 3v across the dropping resistor. Size resistor accordingly)

If you breadboard it - you should be able to test the output levels by manually interrupting the path. If this doesn't work, check the LED for output and voltage drop across it should be ~2v.

Is there a datasheet for the opto device you bought?

There should be no connection to the opto device's output transistor base. [there may have been in the original]

Sorry for my exasperation.... make that 10000 words.

 

[RSX11M+]

Try this.... (dug out an old laptop and corrected the second drawing)

But I still need a datasheet on the opto device.

 

[RSX11M+]

Just checked back through your posts and found the link to the auction for your opto device.

Specification:

Product Name	Slotted Optical Switch
Model	HY860C
Output Type	Photo Transistor
Peak Emission Wavelength	940nm
IR Diode Forward Current	50mA
IR Diode Reverse Voltage	5V
Transistor Power Dissipation	75mW
Transistor Collector Current	20mA
Photo Transistor Collector-emitter Voltage	30V
Photo Transistor Emitter-collector Voltage	5V
Diode Power Dissipation	100mW
Operating Temperature Range	-55~100 Celsius Degree
Number of Pins	4
Slot Width	3.2mm/1/8''
Slot Depth	8mm/5/16''
Pin Length	9mm/0.35''
Pitch	7mm/0.28'', 2.5mm/0.1''
Hole Dia.	3mm/0.12''
Total Size	25 x 23 x 6mm/1'' x 0.9'' x 0.2''(L*W*H)
Material	Plastic, Metal
Color	Black
Net Weight	9g
Package Content	10 x Slotted Optical Switch w Bracket

There isn't enough there for me to help with pin identification. The spec does say 50ma on the LED is ok, so forget my worries about that.

The photo transistor is a two pin device. [base not accessible] However, the Collector is not interchangeable with the Emitter. Does the package clearly identify them? The emitter of an NPN must be grounded in your application.

See if any of that helps.