TRS-80 (IV) help?

From: Dave Dunfield <>
Date: Mon Oct 11 20:45:57 2004

Hi Guys,

Picked up another big load this weekend, and am just starting to go
through it - Item#1 is a TRS-80 Model IV.

When I first powered it up, it sucked on the Empty bottom drive for
a couple of seconds, then prompted with "Cass?" and entered ROM basic.
Tried a Model IV boot disk and go the same result - so I removed the
drive and cleaned it (machine has been sitting a long time).

Now, it powers up, selects the drive and "hangs" - does not move on
to the "Cass?" prompt - I've checked all connections and socketed
chips, and everything is clean and looks OK. Have reseated everthing
several times.

A few of observations:

- If I hold RESET while I power up the machine, the drive motors still
  come on, but I do not get a select - the select appears to be happening
  under software control.

- If I disconnect the disk controller board ribbon cable, the machine
  powers up at the "Cass?" prompt - in this case, I believe the ROM
  startup sees that there is no disk system and enters ROM basic,
  thinking that it is a diskless unit.

- If I power-up/reset while holding BREAK, it also gives the "Cass?"
  prompt - after briefly selecting the drive - looks like BREAK very
  soon after power-up can interrupt the boot process, and ROM BASIC
  comes up normally.

- I never see the drive seek - it selects, but does not seek.
  If I manually move the drive head out during power-off, it DOES NOT
  seek back to track-0 after selecting the drive when I power it on.

- Twice so far in a couple of hours of working on it, I have seen the
  prompt "Diskette?" (no cursor) after powering on the machine (with
  disk controller connected and not holding BREAK). I cannot make this
  prompt come up reliably.

It looks to me as if something in it's interaction with the disk controller
is hanging the machine.

Anyone here knowlegable in TRS-80's?

Can anyone tell me what the Model IV is *SUPPOSED* to do on power-up, both
with and without a boot disk in the drive (I have no documentation at all).

Any pointers to service documentation? ROM listings? Other information on
servicing a model IV - any idea how I can further diagnose this problem?

Any help at all would be greatly appreciated!

dave04a (at)    Dave Dunfield
dunfield (dot)  Firmware development services & tools:
com             Vintage computing equipment collector.
Received on Mon Oct 11 2004 - 20:45:57 BST

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