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TRS-80 Model 1: Expansion Unit / Disk Drive problems

M

memphis

Member
Joined
Oct 20, 2012
Messages
25
Location
PA USA
Little help please.
I recently got a model I system unit fixed and am now moving on to
an unknown EI and drive set.
This is the first time I've ever worked with a TRS-80 EI and drives.
I've looked over the documentation and service manuals
So here's what I have:
An early version expansion unit with an active type cable and two drives.
I've used deoxit on the EI and drive cables.
The system unit seems to be connected as print peek(16561)+peek(16562)*256 shows 64K
whereas w/out the EI that yields 32K. Voltages look right in the EI.
Where I'm stuck is the drives. I have the terminated drive in the 0th connector.
The first two connectors are missing the orientation key but I oriented the connector
onto the drive as if it was there; at the bottom matching the notch on the drive edge connector.
When I power up the system unit I get a drive spin up about 1 in 5 times but only an
access LED light up about 1 in 10 times. Further, it never seems to never actually read the floppy as
the system immediately goes to the BASIC prompt. I have the drive all apart and can probe
everything. The rails look good; the drive head seems to be able to move freely/correctly.
It was very clean.
I have worked/reseated the connectors many times. Perhaps the edge card connectors at
all cables still need more work? Does this seem like a cable/connector issue?
I could move the terminator to the '61 drive and try that drive alone for booting unless
someone can offer other troubleshooting procedures.
I know someone here has been through this... right?
Thanks!
 
Checking the drive controller chip access

Checking the drive controller chip access

I received some help on the TRS-80 Yahoo group for this as follows. I am reposting it some someone
doesn't waster their time duplicating this information.
I will be trying out these procedures soon.

[h=2] Re: Model 1 Expansion/Drive help [/h]
[h=4]Fri Apr 11, 2014 1:59 pm (PDT) . Posted by:[/h] [h=3] trsusbcf [/h]​

Your system does not seem to recognize the FDC (WD 1771 if SD; most often both 1771 and 1791 if a doubler has been installed) I guess you don't have a doubler.

DO REMOVE ALL FLOPPIES FROM YOURE DRIVES WHEN TESTING

To check the 1771 you might wish to read the the status register (37ECh)
Something like ? Peek(FDC-status-address) [substitute decimal value of 37ECh]
You might wish to check the ready bit of the Floppy circuitry:
poke drive_select_address, drive_n
Substitue decimal value of 37E0h for drive_select_address and 1, 2, 4, 8 for drive 0, 1, 2 or 3, respectively. Drive LED (and motor on) should last for about 4 sec following 1 write to 37E0h.
Reading the FDC status with drive LED's on should give other results compared to drive LED's off.
You might also wish to check the Track-0 bit by
Next you might wish to test track, sector, and data ragisters of the 1771.
For this purpose, the track and sector register should behave as RAM. Writing any value, followed by reading must return the same value. I don't know whether this also holds for the data register, but, in my experience, it is not mandatory to test the 1771 data register: if status, track and sector register are OK, data register will most probably be OK, too.
Sector and track registers are at 37EEh and 37EDh (though I don't recall which register resides at which address). Use POKE and PEEK to test them, e.g., by writing a certain value to one of the registers, and a random value to the other register and reread the first written register. Doing so, you might be sure addressing is OK.
Good Luck, remember, your signs are not related to floppy drive cables.
​
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HEre's a simple one: Do you know if the E/I in question has a doubler board installed? Look though the gap around the floppy/parallel port card edge connector(s) and see if there's a daughter board plugged in. IF there is, well, try sticking a finger in there and giving the board a little wiggle/press to make sure it's seated. I don't know if this is a *common* problem but pretty much every time I've packed up/unpacked my TRS-80's E/I the board loses contact and the symptoms are essentially what you describe. (No floppy activity/system drops straight to BASIC.)
 
Right you were!
Thanks!
If I every open that EI again I'm going to find some way
to secure the board. Pehaps two thin bolts and holes through both boards.
I finished the repairs and here's the results.
http://imgur.com/a/lmaRt
 
Drilling a hole through the boards seems like a somewhat radical solution. A better/less drastic fix would probably be to replace the 1771 socket with a good-quality machine pin one. (Maybe even splurge on gold plating.)
 
I suppose you are right. Replacing the socket with gold machine headers would be an excellent idea.
I've heard that the Tandy version wedged foam between the board and the case to hold it in. Not bad either.
 
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