13 Jul
2020
13 Jul
'20
2:18 p.m.
Anyone on list repair or rehab Tandon TM848 drives?? I have a 4 or so of
the slimline drives from some Tandy Model 12/16b units that don't seem
to spin at all, and I've hooked them up to the same PSU that a TM848E
successfully runs on, so I am guessing it's not a PSU issue. (Though, my
understanding of 8" drives is extremely minimal, so...)
If I could get just 2 of them working, that'd put a few 12/16b units
back in operation.
Jim
--
Jim Brain
brain at jbrain.com
www.jbrain.com
13 Jul
13 Jul
3 p.m.
Shouldn't be too difficult to troubleshoot; have you got the manual?
Start by checking the 24V > 12V regulator...
m
----- Original Message -----
From: "Jim Brain via cctalk" <cctalk at classiccmp.org>
To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at
classiccmp.org>
Sent: Monday, July 13, 2020 2:18 PM
Subject: TM848 repair?
Anyone on list repair or rehab Tandon TM848 drives? I
have a 4 or so of
the slimline drives from some Tandy Model 12/16b units that don't seem
to spin at all, and I've hooked them up to the same PSU that a TM848E
successfully runs on, so I am guessing it's not a PSU issue. (Though, my
understanding of 8" drives is extremely minimal, so...)
If I could get just 2 of them working, that'd put a few 12/16b units
back in operation.
Jim
--
Jim Brain
brain at jbrain.com
www.jbrain.com
3:11 p.m.
On 7/13/20 12:00 PM, Mike Stein via cctalk wrote:
Shouldn't be too difficult to troubleshoot; have
you got the manual?
Start by checking the 24V > 12V regulator...
Second that! I've had to replace more than one regulator on 848s; also
the 100 ohm resistor (R1) and electrolytic capacitor(C6) on the input
side of the regulator.
--Chuck
5:05 p.m.
On 7/13/2020 2:11 PM, Chuck Guzis via cctalk wrote:
On 7/13/20 12:00 PM, Mike Stein via cctalk wrote:
Thanks for the tip.? On one, the 10ohm (yep, 10) is cooked, so I need to
get another one.? Looks like 1/2W, but anyone know for sure?? The
schematic just notes the resistance and identifier.? It could be 1W...
The other 1 I have on the bench looks to have a good resistor, but I
will check the VR next.
Jim
--
Jim Brain
brain at jbrain.com
www.jbrain.com
Shouldn't be too difficult to troubleshoot;
have you got the manual?
Start by checking the 24V > 12V regulator...
Second that! I've had to
replace more than one regulator on 848s; also
the 100 ohm resistor (R1) and electrolytic capacitor(C6) on the input
side of the regulator.
--Chuck
6:23 p.m.
On 7/13/20 2:05 PM, Jim Brain via cctalk wrote:
--Chuck
Thanks for the tip.? On one, the 10ohm (yep, 10) is cooked, so I need to
get another one.? Looks like 1/2W, but anyone know for sure?? The
schematic just notes the resistance and identifier.? It could be 1W...
Given the power consumption (up to 1.2A) on the 24V line, I'd play it
safe and go with 2W.
--Chuck
7:58 p.m.
On 7/13/2020 5:23 PM, Chuck Guzis via cctalk wrote:
On 7/13/20 2:05 PM, Jim Brain via cctalk wrote:
--Chuck
I also am at a loss on the 4u7 cap.? The one I am replacing is a black
unit with a tapered + end, but I am not finding exact duplicate.
Will this work:
https://www.digikey.com/product-detail/en/nte-electronics-inc/NEH4-7M50AA/2…
--
Jim Brain
brain at jbrain.com
www.jbrain.com
Thanks for the tip.? On one, the 10ohm (yep, 10)
is cooked, so I need to
get another one.? Looks like 1/2W, but anyone know for sure?? The
schematic just notes the resistance and identifier.? It could be 1W...
Given the
power consumption (up to 1.2A) on the 24V line, I'd play it
safe and go with 2W.
--Chuck
9:01 p.m.
On 7/13/20 4:58 PM, Jim Brain via cctalk wrote:
On 7/13/2020 5:23 PM, Chuck Guzis via cctalk wrote:
Yes, that will work, but so will almost any garden-variety electrolytic
rated at 35-50WVDC. The cap doesn't handle any AC--it's there mostly to
keep the voltage regulator from oscillating.
--Chuck
On 7/13/20 2:05 PM, Jim Brain via cctalk wrote:
? --Chuck
I also am at a loss on the 4u7 cap.? The one I am replacing is a black
unit with a tapered + end, but I am not finding exact duplicate.
Will this work:
https://www.digikey.com/product-detail/en/nte-electronics-inc/NEH4-7M50AA/2…
Thanks for the tip.? On one, the 10ohm (yep, 10)
is cooked, so I need to
get another one.? Looks like 1/2W, but anyone know for sure?? The
schematic just notes the resistance and identifier.? It could be 1W...
Given the
power consumption (up to 1.2A) on the 24V line, I'd play it
safe and go with 2W.
--Chuck
6:23 p.m.
On 7/13/2020 2:11 PM, Chuck Guzis via cctalk wrote:
On 7/13/20 12:00 PM, Mike Stein via cctalk wrote:
You, my good man, need some funds.? I will send funds so you can grab a
beer or something!
The one unit has a bad resistor (need to order), while the other has a
shorted C6 (temp replaced with a radial cap while I order one of those.?
That one boots now.
I was dreading trying to debug these things, and no doubt they won't all
be this easy, but some early success foes wonders for confidence to
continue.? Thanks for the help!
Jim
--
Jim Brain
brain at jbrain.com
www.jbrain.com
Shouldn't be too difficult to troubleshoot;
have you got the manual?
Start by checking the 24V > 12V regulator...
Second that! I've had to
replace more than one regulator on 848s; also
the 100 ohm resistor (R1) and electrolytic capacitor(C6) on the input
side of the regulator.
--Chuck
7:10 p.m.
On 7/13/20 3:23 PM, Jim Brain via cctalk wrote:
You, my good man, need some funds.? I will send funds
so you can grab a
beer or something!
The one unit has a bad resistor (need to order), while the other has a
shorted C6 (temp replaced with a radial cap while I order one of those.?
That one boots now.
I was dreading trying to debug these things, and no doubt they won't all
be this easy, but some early success foes wonders for confidence to
continue.? Thanks for the help!
Don't mention it--happy to help out!
--Chuck
8:09 p.m.
On 7/13/2020 6:10 PM, Chuck Guzis via cctalk wrote:
Don't mention it--happy to help out!
I am especially impressed, for a few reasons.? Backstory:
* I snagged 2 Model 12s at a CoCoFEST! a number of years ago during
the show auction.? NO KBs
* I then spent too much I am sure buying extra boards from a chap
outside Atlanta who seemed to have sold these units for years.
* Peter Cetenski was gracious enough to get me a few bootable floppies
to try.
* Then, when picking up the Atlanta parts in Chicago (they came via
someone's back seat, I by plane), Jason Timmons loaded me up with
more Model II stuff (external drive, front bezels, and a few Model
IIs, including a batch of KBs.
* Finally, at Tandy Assembly 2018, I picked up 2 external HDDs for not
much coin)
* But, I have been sitting on all this collection in unusable form
since then.? It's taking up valuable space and I know I don't need
it all, so I really need to get the units working I want, and then
move the rest to a new home.
* Still, all of the units collectively seemed a daunting task,
especially in light of my not knowing anything about the platform. I
don't even know how to list a dir in TS-DOS 2.0a (or whatever it is
called).? LS-DOS uses dir, so there's that.
Of the 4 units, 1 requires a new resistor (well, at least 1 new
resistor), 2 were bad caps (now booting), and 1 has a good mech (swapped
logic board with another one), but the logic board has another issue.?
Resistor is good, cap is good, and VR is outputting 11.9VDC.? The
stepper moves when booted, and the drive motor also looks to be running
well.? I can see the LED showing the index pulses, but not sure where I
should start (I have it sitting in a working mech, so I know all mech is
at least marginally OK (was booting from the mech with another logic board).
Jim
--
Jim Brain
brain at jbrain.com
www.jbrain.com
3:18 p.m.
On 7/13/2020 2:00 PM, Mike Stein wrote:
Shouldn't be too difficult to troubleshoot; have
you got the manual?
Start by checking the 24V > 12V regulator...
As for a manual, I have this:
https://www.scss.tcd.ie/SCSSTreasuresCatalog/hardware/TCD-SCSS-T.20141115.0…
I don't see the VR section in that, though.
3:29 p.m.
On 7/13/20 12:18 PM, Jim Brain via cctalk wrote:
On 7/13/2020 2:00 PM, Mike Stein wrote:
If it's the same document that I have, PDF page 18, second-to-last page
of schematics, near the bottom, near the legend "DC POWER CONNECTOR"
--Chuck
Shouldn't be too difficult to troubleshoot;
have you got the manual?
Start by checking the 24V > 12V regulator...
As for a manual, I have this:
https://www.scss.tcd.ie/SCSSTreasuresCatalog/hardware/TCD-SCSS-T.20141115.0…
I don't see the VR section in that, though.
4:57 p.m.
----- Original Message -----
From: "Chuck Guzis via cctalk" <cctalk at classiccmp.org>
To: "Jim Brain via cctalk" <cctalk at classiccmp.org>
Sent: Monday, July 13, 2020 3:29 PM
Subject: Re: TM848 repair?
On 7/13/20 12:18 PM, Jim Brain via cctalk wrote:
----------------------------
Which document is that? I find it on PDF page 85 of the OEM Operating and Service Manual
TM-848-1 and TM-848-2 Disk Drives, Sheet 4 of 5.
m
On 7/13/2020 2:00 PM, Mike Stein wrote:
If it's the same document that I have, PDF page 18, second-to-last page
of schematics, near the bottom, near the legend "DC POWER CONNECTOR"
--Chuck Shouldn't be too difficult to troubleshoot;
have you got the manual?
Start by checking the 24V > 12V regulator...
As for a manual, I have this:
https://www.scss.tcd.ie/SCSSTreasuresCatalog/hardware/TCD-SCSS-T.20141115.0…
I don't see the VR section in that, though.
5:06 p.m.
On 7/13/2020 3:57 PM, Mike Stein via cctalk wrote:
----------------------------
Which document is that? I find it on PDF page 85 of the OEM Operating and Service Manual
TM-848-1 and TM-848-2 Disk Drives, Sheet 4 of 5.
It's the first one I linked (above).? It looks to be an older manual.? I
agree the one you linked has more information, so I grabbed both.
Jim
As for a
manual, I have this:
https://www.scss.tcd.ie/SCSSTreasuresCatalog/hardware/TCD-SCSS-T.20141115.0…
I don't see the VR section in that, though.
If it's the same document that
I have, PDF page 18, second-to-last page
of schematics, near the bottom, near the legend "DC POWER CONNECTOR"
--Chuck
5:01 p.m.
On 7/13/2020 2:29 PM, Chuck Guzis via cctalk wrote:
If it's the same document that I have, PDF page 18, second-to-last page
of schematics, near the bottom, near the legend "DC POWER CONNECTOR"
--Chuck
Eyesight is failing. I had the same doc.
--
Jim Brain
brain at jbrain.com
www.jbrain.com
3:02 p.m.
On 7/13/20 11:18 AM, Jim Brain via cctalk wrote:
Anyone on list repair or rehab Tandon TM848 drives?? I
have a 4 or so of
the slimline drives from some Tandy Model 12/16b units that don't seem
to spin at all, and I've hooked them up to the same PSU that a TM848E
successfully runs on, so I am guessing it's not a PSU issue. (Though, my
understanding of 8" drives is extremely minimal, so...)
If I could get just 2 of them working, that'd put a few 12/16b units
back in operation.
The Tandon 848 is not one of my favorite drives. There is an option not
to pass the Motor On/ signal unless a disk is loaded and the drive door
is closed. Check U16 pin 8, which should be high for MOTOR ON.
It seems more like an oversight that all 4 drives don't spin. Be aware
that the 848's motor controls are different from 5.25", where one line
controls all motors. The 848 uses pins 4,6,8 and 24 on the interface to
control the motor--each drive has a jumper that dictates which line will
be used. (MC 1-4).
--Chuck
3:21 p.m.
On 7/13/2020 2:02 PM, Chuck Guzis via cctalk wrote:
On 7/13/20 11:18 AM, Jim Brain via cctalk wrote:
> The Tandon 848 is not one of my favorite drives. There is an option not
> to pass the Motor On/ signal unless a disk is loaded and the drive door
> is closed. Check U16 pin 8, which should be high for MOTOR ON.
I will do so.
>
> It seems more like an oversight that all 4 drives don't spin. Be aware
> that the 848's motor controls are different from 5.25", where one line
> controls all motors. The 848 uses pins 4,6,8 and 24 on the interface to
> control the motor--each drive has a jumper that dictates which line will
> be used. (MC 1-4).
Yep, one of the drives was set to DS2, so I moved it back to DS1 so I
could test as a primary drive.? I agree the drives would be different
from 5.25" ones, but I connected them to the same
PSU that runs my
TM848E successfully.? It seems strange that a working PSU that
drives a
TM848E would not supply enough or the right voltage for a TM848-02.
Jim
1509
days inactive
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days old
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