24 replies to this topic

[Bob White]

OK so I bought an ETX-60 for cheap ($45) with the intent to refurb it and flip it.
Actually that all worked well and I have a buyer for $100.  Scope is super tuned and working well.

It has a 494 hand controller.

However, the night of the eclipse I was using it and while it was tracking I started seeing some crazy stuff.
Random PROC trap 2 messages and other odd things like reboots. ONLY when it was tracking.  No other time.
The more I kept trying to use it the worse random issues happened.

A few days later and now it won't even power on. 
I figured it was a bad cable.  So I made and soldered on a new cable (yes soldered inside to the board.  ONLY way on a 494).

I get a few blinks from the display backlight LEDs and an odd CLICK sound.
Click sound?  No relays on this so WTH?  Read on... click is coming from a tantalum capacitor!

I decided to have a look closer and WOA... An old tantalum capacitor!  
LX200 classic people know these very well.
Using a MIC the click is coming from this capacitor..  WTH?

So I figure before I toss this hand controller I would replace the CAP.
Do I need to replace it with a tantalum?  Or can I replace it with a ceramic or electrolytic?

Thoughts?

 

Bob

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Edited by Bob White, 23 May 2022 - 06:46 PM.

[terrypaula]

Thosw tings are noisy aren't they?  Have you looked or done an internet search for the equivalent cap?

[OzAndrewJ]

Gday Bob

Do you have some fine probes that allow you to do a continuity check ???

Dave Groski and myself have been doing a lot of testing of how the contrast works for

different mounts as this affects whether the new Formike LCDs will work during boot or not.

We suspect one of the electro caps might be failing, but it is a 100uF unit

and the epoxy type units dont come in that size ( yours looks like a 10uF )

I assume the 1000uF elctro is for the +12V to +5V regulation

so no idea what the 10uF is for.

Can you see if either leg of the unit is connected to the contrast pin on the LCD

and if not, check the +ve leg against the input and output of the +5V regulator

( ie the 1000uF might be a storage cap and the 10uF assists in smoothing. )

This type of cap normally fails by going short circuit so may be shorting

the +5 to ground at times, which would explain the symptoms.

 

Andrew Johansen Melbourne Australia

[Bob White]

Andrew, don't think this is related to the LCD as I no longer get the power on "beep" anymore.
Just a click sound from that Cap...

The traces for it go directly to the processor as you can see from the picture. But yes one does run up to the LCD but I cannot tell without tracing it is it's coming from under the proc.

Back in my old days of design (80's) you used a Tant Cap for for solid crystal timing. An electrolytic usually was to big and not fast enough for the same result. 
But things have changed since then.

Anyway I would be glad to check what you like.  A bit more detail on what to check would be great.  Like pins on the LCD you want etc.

 

Bob

Edited by Bob White, 23 May 2022 - 09:19 PM.

[Bob White]

Andrew,
and yes I have a meter and other tools. And I know how to use them. 
Just not a logic analyzer LOL...

Bob

Edited by Bob White, 23 May 2022 - 09:25 PM.

[OzAndrewJ]

Gday Bob

OK, i can see the +ve leg of the tant appears to go to the 10th pin on the CPU.

It looks like the CPU is a 52 pin 68HC11E1CFNE2

and if so, that pin is the reset pin.

I dont have a detailed circuit for the 494, but i did make up ( an unverified )

circuit diag for the 497 ( Rev E   PCB )

In that, i found that the reset pin on the 68HC11 is fed from a weird supply

that i couldnt fully trace, but the cap in question goes directly between

the reset pin and ground.

( In the LX200GPS, the reset pin is controlled by the mainboard PIC )

If it is shorting, then it would certainly cause grief

but the rest is above my paygrade

 

Andrew Johansen Melbourne Australia

[OzAndrewJ]

Gday Bob

Just not a logic analyzer

They are only $10, but i dont think it will help here

as if the cap is connected to the 10th pin,

then its something i know nothing about :-)

 

Andrew Johansen Melbourne Australia

[Bob White]

Andrew.  So for the hell of it I dug a 10uF electrolytic out of my parts bin and soldered it on. Removing the old tant.
Now I get some life!
The display turns on but it's all grey.  The back light blinks 3 times then off.
No more "click sound".  That Tant cap clearly was arcing internally!

Based on what I know (which you know better than I) I think the ROM FLASH is now done.  Meaning it got erased or cannot load.
I know with the 494 is jacked if the ROM flash goes south.  And you cannot flash it without getting super into it and using a chip flash tool. 
I remember Richard explaining what it takes to update a 494 from way back!  No thanks.

So with that said, I have a display that works AND a rubber keypad.

WHO WANTS IT?

LOL

 

Bob

 

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[Bob White]

Andrew that tant cap failing and arcing internally, RESET and clearly jacked this AS unit.

As you said, it caused GRIEF with the reset pin....  LOL

 

With the 10uF cap I now get the same result over and over on power up.
The display is on but it's a blank display and 3 blinks of the LED backlights.

The proc can't boot anything as the ROM is erased. So I speculate.

I suggest ANYONE with an old AS494 like this one, replace that Tant CAP right away or suffer the same fate.

Bob

 

 

Edited by Bob White, 23 May 2022 - 10:28 PM.

[OzAndrewJ]

Gday Bob

I actually found some 494 schematics and detailed info on resetting the 494.

It doesnt appear to need a dedicated chip loader, but does require some jumpering and switches

to put it into loader mode.

Can send you some details if reqd.

 

Andrew

[Bob White]

Gday Bob

I actually found some 494 schematics and detailed info on resetting the 494.

It doesnt appear to need a dedicated chip loader, but does require some jumpering and switches

to put it into loader mode.

Can send you some details if reqd.

 

Andrew

Sure Andrew!  If I can make this thing work again I will give it a try!
Send it to me please.

Thank buddy,
Bob

[OzAndrewJ]

Gday Bob

 

PM sent

 

Andrew Johansen Melbourne Australia

[DAVIDG]

   I figured out how to bring a some "dead"  Autostar 497 back to life by clearing a bit in the HC6811. Here is an article published here that explains how to put the HC6811 into bootloader mode that allows the firmware to be reloaded

 https://www.cloudyni...StarRevival.pdf

This may help you  get  your 494  to wake up. 

    I have also seen 497 act the the way your 494 is when the negative voltage to the display is missing. Look at a  sharp angle in strong  light at the display and see if you see  the text. If so the negative voltage made to control the contrast is missing causing the display to be at the lowest contrast making the text invisible. You can short the contrast line on the screen to ground and that will force the contrast to be at the highest and the text visible if the unit is correctly booting. The contrast line is the 2nd pin in from the  right on the white connector for the LCD screen and the ground is the 1st pin on the right of the white connector. 

 

                - Dave 

 

              

[Bob White]

Hi Dave, it's not the display as the unit does not beep, slew with arrows, etc.
Backlight LEDs also do not come on. They flash 3 times and off.
Thanks for the PDF.  I will save it for the future if my 497 ever does this.

Andrew sent me a procedure for the 494 and it is similar to this.

 

Thanks,

Bob

[DAVIDG]

Hi Dave, it's not the display as the unit does not beep, slew with arrows, etc.
Backlight LEDs also do not come on. They flash 3 times and off.
Thanks for the PDF.  I will save it for the future if my 497 ever does this.

Andrew sent me a procedure for the 494 and it is similar to this.

 

Thanks,

Bob

 Bob,

   Keep us posted if you repair your 494. Just to clarify the article about fixing a 497 discusses I believe very similar behavior as a 494 with the bit that points to the external memory in the wrong state. That is the arrow to slew the scope does work  but it show some life in flashing LEDS or beeping when it boots then nothing. 

    What I believe happens is when the HC6811 has the power interrupted from a non- normal  shut down,  the bit that points to the external memory gets written in the wrong state. So when the Autostar tries to boot again it doesn't see the external memory hence the firmware isn't loaded.  Once you clear that bit, you can boot the Autostar in Safe Loader mode and reload the firmware. 

   I haven't played with a 494 but it looks like you can update/reload  the firmware  but it required the use of  special cable that plugged into the scope instead of using RS232 port on the 497's which the 494's don't have. So my guess is that the special cable for the 494 is  RS232 to TTL converter. and communication to the HC6811 is direct TTL to the port on it.  If that is the case then one could use a USB to TTL converter to do the same to run the program to reload the firmware.  

   Again if you get your 494 working it would great if you post the procedure.

 

               - Dave 

[OzAndrewJ]

Gday Dave

 

I haven't played with a 494 but it looks like you can update/reload  the firmware  but it required the use of  special cable that plugged into the scope instead of using RS232 port on the 497's which the 494's don't have. So my guess is that the special cable for the 494 is  RS232 to TTL converter.

There is no "easy" way to update the firmware in the 494s, but you can update user data/tours etc.

The special cable is actually an rs232 to "bitbanged" I2C converter, as it effectively ties into the Aux bus.

As such, to use it requires the Hbx to be running and connected to the mount

Meades cable for this was the 506

 

The method used in the 494 instructions remotely powers the Hbx

and uses the std Tx/Rx lines to talk to the main CPU

and shorting jumper clips to set pins puts the CPU into a special diagnostic mode.

 

Andrew Johansen Melbourne Australia

[Bob White]

Gday Dave

 

There is no "easy" way to update the firmware in the 494s, but you can update user data/tours etc.

The special cable is actually an rs232 to "bitbanged" I2C converter, as it effectively ties into the Aux bus.

As such, to use it requires the Hbx to be running and connected to the mount

Meades cable for this was the 506

 

The method used in the 494 instructions remotely powers the Hbx

and uses the std Tx/Rx lines to talk to the main CPU

and shorting jumper clips to set pins puts the CPU into a special diagnostic mode.

 

Andrew Johansen Melbourne Australia

Andrew, I assume using the RX/TX lines per those instructions it is  TTL levels not true RS232 voltage levels?

Bob

[DAVIDG]

 Yes  TTL level to  the HC6811 and powering up the Autostar with the  two pins on HC6811 to ground which will put  it in boot loader mode.   You'll need  something like  a FT232RL USB to TTL converter and a program like HCLOAD  to down load the ROM file back into the 494. If you use HCLOAD also download the Key generator program that will allow you to run the program without any limits. 

   As I said I did something very similar to get some dead 497's to come back to life and Andrew was nice enough to send me the same information he sent  you. 

 

                    - Dave 

[Bob White]

 Yes  TTL level to  the HC6811 and powering up the Autostar with the  two pins on HC6811 to ground which will put  it in boot loader mode.   You'll need  something like  a FT232RL USB to TTL converter and a program like HCLOAD  to down load the ROM file back into the 494. If you use HCLOAD also download the Key generator program that will allow you to run the program without any limits. 

   As I said I did something very similar to get some dead 497's to come back to life and Andrew was nice enough to send me the same information he sent  you. 

 

                    - Dave 

Yes and this presents the first problem.  My USB to RS232 is not TTL for obvious reasons as I use it on my 497's and LX200 GPS's.
I managed to buy a 494 for $15 with a dead display, probably going to make a good 494 from it and put this project on the shelf for now.  Like I want to spend yet another $20 on a USB-rs232 TTL for just this.  NOT....  Throw good money after bad..  

So you know I am buying bum Meade ETX's, tuning and fixing them, and donating them to schools or selling them to people at very low profit if any.  So it's a labor of love and thus costs have to be contained.

Edited by Bob White, 26 May 2022 - 03:48 PM.

[OzAndrewJ]

Gday Bob

If you have a breadboard and a max232, you can make an rs232 to TTL converter for a few dollars

but thats hard work

With the increase in popularity of Arduino boards there are

lots of off the shelf "shields" dirt cheap.

This will plug onto a normal rs232 converter

https://www.ebay.com...AyABEgI5bfD_BwE

 

Or get an "FTDI" based Arduino USB to TTL module that you can wire as you want

https://www.ebay.com...CLK|clp:2047675

 

Andrew Johansen Melbourne Australia

[Bob White]

Gday Bob

If you have a breadboard and a max232, you can make an rs232 to TTL converter for a few dollars

but thats hard work

With the increase in popularity of Arduino boards there are

lots of off the shelf "shields" dirt cheap.

This will plug onto a normal rs232 converter

https://www.ebay.com...AyABEgI5bfD_BwE

 

Or get an "FTDI" based Arduino USB to TTL module that you can wire as you want

https://www.ebay.com...CLK|clp:2047675

 

Andrew Johansen Melbourne Australia

I actually have a Raspberry Pi 3B that has TTL RS232 but then I have to deal with Linux which I have no problem doing, but more of a project that I want to do right now.

[Bob White]

OK latest news... I swear I may give up on all this refurbing scopes as the changes over time Meade made can be frustrating.

So as I said I bought for cheap a 494 that the seller said had a bad display.  He said the scope still worked and slewed.
Today that controller arrived.
Well holy mother of Meade....  The case is a glued together one not screwed together...  China costs savings!
In fact it is super glued together.  It does not have the usually plastic case locking tabs you can snap on most modern cases to take them apart. 
I literally had to pry it apart breaking the glue spots.
But... cheap glue and the case halves were easily separated.

Anyway the circuit board inside also does not have the holes in the board to allow you to put a glued together 494 board in a screwed together 494 case!
So I can't move the good board from this 494 into the other case making a good AS494 screw together case! HEAD SLAP!

NOW the good news.  This supposed bad display 494..... Well the screen is fine!  After I pried it apart I found the display cable was half cocked and not assembled properly!
I reseated the cable and this 494 now works great!

That leaves me with this dead autostar, a good case and keyboard, and good display. I just need to get time to see if I can recover the board.

In the end it all worked out.  Cost me a few more bucks but the guy that bought this tuned and refurbed ETX-60 scope, should be happy.  I just have to say, too much work to take a $45 dollar ETX-60, spend a day tuning and fixing it, spend extra bucks on another AS494, only to sell it for $100.  I made nothing on it and in fact lost. 

And that is fine it's going to a good home with a person new and interested in astronomy.

 

Edited by Bob White, 26 May 2022 - 05:31 PM.

[OzAndrewJ]

Gday Bob

The dead board you have, is it a 497 or 494 ????

I have just been looking at an old 494 ROM i have re how it maps the registers and memory

and i suspect there is an error in the pdfs for the memory address circuits.

If you have a dead 494, and have a bit of time, could you do a continuity test on 2 pins

to see if they are wired the way i suspect ( based on 497 mapping )

as the current code doesnt match the schematics

 

Andrew Johansen Melbourne Australia

[Bob White]

Gday Bob

The dead board you have, is it a 497 or 494 ????

I have just been looking at an old 494 ROM i have re how it maps the registers and memory

and i suspect there is an error in the pdfs for the memory address circuits.

If you have a dead 494, and have a bit of time, could you do a continuity test on 2 pins

to see if they are wired the way i suspect ( based on 497 mapping )

as the current code doesnt match the schematics

 

Andrew Johansen Melbourne Australia

It's a 494.  Yes I can do some continuity checks.  Let me know what pins.

 

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[OzAndrewJ]

Gday Bob

The pins in question are the 2 off 68HC11 pins B7 and A3

and the Flash memory A15

 

Based on the way Meade addresses the Memory

B7 = 0 means RAM, B7 = 1 means Flash or LCD

The Flash chips have 64k pages but Meade break them into 32k sections for use

so simple 16bit mapping doesnt work, the Msb mapping has to be handled manually

ie

Chip page 0 = x0000 to xFFFF

Meade map this into Page x00-8000 to xFFFF

                                           x01-8000 to xFFFF

To do this, they pinch the Msb of PortB as part of the chip select routine

and manually address the Msb using a mapped byte ( in the 497s, this is Pin A3 )

As such, they use the A6,A5,A4 bytes to address the 64k Flash Chip segment

and A3 to select the x0000-7FFF or x8000-xFFFF portion

then B6..B0 + C7..C0 gives the rest of the address

 

In the schematics, on the 494CPU_3.pdf

B7 maps to Flash A15, and this goes to the Flash chips as A15 ( which i think is wrong )

    and also the 494Log.pdf as part of the chip select ( which seems correct )

Based on the code, ( and the 497 diags i have )  the Flash chips A15 is not connected to B7

it should be connected to pin A3 ( which is shown as only having a pulldown to ground )

B7 should only be tied to the U5D in the top left of the  LOG.pdf circuit

Soooooo

1) Is CPU Pin A3 connected to Flash Pin A15  ( it should be )

2) Is CPU Pin B7 connected to Flash Pin A15 ( it shouldnt be )

 

Andrew Johansen Melbourne Australia