Issue with Track 0 sensor on 1050 Tandon

[Retrobecanes]

@_The Doctor__, I will double check the solder joints and connections and report back.  What testing would you then recommend on 3086?

 

@kheller2, for #3, Yes they are both TANDON.  In the case that you mention, yes I get repeated boot errors and the drive continues to spin.

[Retrobecanes]

Here is a picture of the solder side of the SIO from board Y.  I checked all pins for continuity on both SIO connectors and I don't find any issues.  I had als reflown the solder joints a few days ago.  Ignore the circles in blue marker, I just marked the locations of the large capacitors to test them out.  They checked out OK.

Is there a way to test the 3086?  Lastly what would be a valid replacement for that IC?

 

 

Edited May 16, 2023 by Retrobecanes

[TGB1718]

If your really stuck getting one of these (seen a few on Ebay, but not many)

You could just take the chip out, if it's not socketed, put a socket in and use 5 general purpose

NPN transistors pushed into the chip sockets.

 

 

[Retrobecanes]

I found some CA3086E on eBay, hopefully they will work.  Also the problem I had with the SIO connector next to the drive ID switch ended up being mechanical.  I noticed that there was actually a broken pin but it was behind the connector and hard to see.  Luckily I have some spare SIO connectors that I salvaged from an 1087 printer and I replaced it.  Now both SIO connectors work but obviously that didn't solve my "boot error" issue.

[Retrobecanes]

@_The Doctor__ and @kheller2, I have an update:

- I replaced the 3086 on board Y, unfortunately no change

- I changed the jumper settings on board Y to match those of board X and moved the ROM from board X to board Y, no change

So the problem is still on board Y as we have already determined that drive assembly Y and all its components work well with board X. 

In terms of behavior, with board Y, when the computer is turned on, the drive just spins but the head never does not move and it eventually displays boot errors on the screen, while spinning.

Could this be a defective component in the stepper driver circuit (U2 or U3)?  There I already know that U7 should be fine as I swapped it from board X with no change.

Or could this be a defective component in the the read circuit (U13, U18-20, U22-24)?

I just don't know if this behavior could be due to read circuitry or stepper driver circuitry, or both....

<sigh>

 

[_The Doctor__]

Hopefully put the jumpers and original eprom back. I would also apply solder in any trace track that is gouged across it's width.

Since the mech works in both drives and the drive isn't stepping forward then back on the bad board, you are left with track zero circuit issues.

At turn on of the drive- does the bad board step the head forward then back? Does the spindle spin as well?

is that different to when that has passed correctly at turn on, as opposed to when the computer is turned on with the drive already on.

 

Edited May 19, 2023 by _The Doctor__

[Retrobecanes]

@_The Doctor__ yes I have already soldered the jumpers back to their original position and put the original ROM back in.  When I turn on system Y, the head does step forward then back and the spindle spins, just like it does in system X.  It seems to behave perfectly normally since I replaced the track 0 sensor.  Actually the startup behavior is exactly the same between the two drives.  The only difference is when I turn the computer on.  With the good drive it rapidly beeps right away and then eventually starts moving the head as it boots the disk.  With the bad, when I turn the computer on, the spindle spins but I don't hear the rapid beeping and the head never moves, it just eventually start displaying boot errors while the drive always spins.

[_The Doctor__]

that's important now we know you should check the front 3086 and the read head circuitry, so flip to the read head circuitry portion of the schematics.

[Retrobecanes]

@_The Doctor__ Oh wow, I didn't realize that there were two 3086 components.  I replaced the one in the back of the board, I guess I will replace the one in the front now and check the signals on U13, U18-20, U22-24 if I can.

[Retrobecanes]

@_The Doctor__ So I replaced the 3086 in the front of board Y but no change...