29 Jul
2014
29 Jul
'14
10:03 a.m.
Hello list!
i`am working on the restoration of my TU56 Drive. It has an overvoltage
damage.
The manual transportlogic control and the transportcontrol by the TD8E
is working correct.
Now i`am in trouble with the G888 Manchester read/write Modules.
Specialy with the adjustment of the zero crossing detector. In the
maintanence manual i could not find any information on the correct
adjustment and originaly the poti is secured by black paint...
Oszi <http://www.familie-rauhut.eu/pic/oszi.gif>
The yellow graph is the output of the first Amplifier witch is amplified
the read heads outputsignal.
The blue signal is the output of the nand driver(7400) after the zero
crossing detector.
In case of the term zero crossing detector, i placed the rising edge of
the output on where the sine wave cross the zero line.
Any usefull hints on the adjustment of the "zero crossing" detector?
Marco
* Englisch - erkannt
* Englisch
* Deutsch
* Englisch
* Deutsch
<javascript:void(0);>
29 Jul
29 Jul
10:32 a.m.
On 7/29/14 10:03 AM, Marco Rauhut wrote:
Any usefull hints on the adjustment of the "zero
crossing" detector?
Yes, don't touch them at all until you get to the point where you can get
it talking to a DECtape controller. If you are getting read errors, THEN
worry about fiddling with the pots.
11:19 a.m.
I have read errors with the unit!
With the TD8E diagnostic software i get an error that block 0 was not found.
I have also bad mc1709 read amplifiers.
So i think i got to adjust them.
Am 29.07.2014 um 19:32 schrieb Al Kossow <aek at
bitsavers.org>:
On 7/29/14 10:03 AM, Marco Rauhut wrote:
Any usefull hints on the adjustment of the "zero crossing" detector?
Yes, don't touch them at all until you get to the point where you can get
it talking to a DECtape controller. If you are getting read errors, THEN
worry about fiddling with the pots.
12:01 p.m.
On 7/29/14 11:19 AM, Marco Rauhut wrote:
I have read errors with the unit!
With the TD8E diagnostic software i get an error that block 0 was not found.
I have also bad mc1709 read amplifiers.
So i think i got to adjust them.
Maybe.
Are you using a PDP-8 formatted DECtape?
Is the controller known to be working?
Can you see clock, mark track and data track output?
Is the clock aligned with the mark and data tracks?
How many 709's were bad, and on which module was it bad on?
12:52 p.m.
Yes, the tape is a PDP-8 formated DECtape.
And yes, the controller working well with an other drive.
I tested all five G888 boards output on the clock track. On all boards i
see the clock sine on the read amplifiers output. On your question i
invetigated that on of the G888 shown always high. At a closer look i
think there is somthing self oszilating on this board....
On three G888 boards i got to change the first read amplifier, and on
one of these i changed the zero level detector OP.
Am 29.07.2014 21:01, schrieb Al Kossow:
On 7/29/14 11:19 AM, Marco Rauhut wrote:
I have read errors with the unit!
With the TD8E diagnostic software i get an error that block 0 was not
found.
I have also bad mc1709 read amplifiers.
So i think i got to adjust them.
Maybe.
Are you using a PDP-8 formatted DECtape?
Is the controller known to be working?
Can you see clock, mark track and data track output?
Is the clock aligned with the mark and data tracks?
How many 709's were bad, and on which module was it bad on?
1:28 p.m.
On Tue, Jul 29, 2014 at 1:52 PM, Marco Rauhut <marco at familie-rauhut.eu> wrote:
Yes, the tape is a PDP-8 formated DECtape.
And yes, the controller working well with an other drive.
I tested all five G888 boards output on the clock track. On all boards i see
the clock sine on the read amplifiers output. On your question i invetigated
that on of the G888 shown always high. At a closer look i think there is
somthing self oszilating on this board....
The G888 is deliberately designed to oscillate, IIRC.
2:20 p.m.
What do you want to say with IIRC ?
I see the input amplifier self oscillate if the remot/off/local switch
is in off position.
If i switch it to remote the output of the inplut amplifier go zero.
But on Interface cable i see some data (noise?) on the read lines.
How got the lines RD0, RD1, RD2, RTT and RMT to be if i have the pdp8
switched on and halted and the TU56 switched on and remote switch in
remote position. All lines 0V or all lines 5 V or the levels jumping around?
Am 29.07.2014 22:28, schrieb Eric Smith:
On Tue, Jul 29, 2014 at 1:52 PM, Marco Rauhut
<marco at familie-rauhut.eu> wrote:
* Englisch - erkannt
* Englisch
* Deutsch
* Englisch
* Deutsch
<javascript:void(0);>
Yes, the tape is a PDP-8 formated DECtape.
And yes, the controller working well with an other drive.
I tested all five G888 boards output on the clock track. On all boards i see
the clock sine on the read amplifiers output. On your question i invetigated
that on of the G888 shown always high. At a closer look i think there is
somthing self oszilating on this board....
The G888 is deliberately designed to
oscillate, IIRC.
30 Jul
30 Jul
9:28 a.m.
On 7/29/14 2:20 PM, Marco Rauhut wrote:
What do you want to say with IIRC ?
I see the input amplifier self oscillate if the remot/off/local switch is in off
position.
If i switch it to remote the output of the inplut amplifier go zero.
But on Interface cable i see some data (noise?) on the read lines.
How got the lines RD0, RD1, RD2, RTT and RMT to be if i have the pdp8 switched on and
halted and the TU56 switched on and remote switch in remote position. All lines 0V or all
lines 5 V or the levels
jumping around?
There is positive feedback (R12) across the slicer op-amp. It is supposed to oscillate
when
the tape isn't moving.
If you've looked at the TC08 maint manual, you'll see that the G888's
weren't supposed to be
adjusted in the field.
If you have a second drive, swap G888's until you can isolate which ones aren't
working, then
try to find where (if) it starts working when you adjust the pot. The best you can do then
is find
the edge excursions where it stops working and center it.
Tuning beyond that gets into setting the clock, mark track, and data tracks which
needs to be done with something more than the basic go/no go performance diagnostic.
12:25 p.m.
Thaks to all helping hands!
I think now i found an answer to my question on pdp8online.com.
Field Sevice Tips <http://www.pdp8online.com/bklatt/703.png>
So i have now adjust my G888 Boards. Function check of the drive follows
now.
On one G888 i have somthing noisy in the scope view. Maybe this is my
problem with the TU56.
Marco
Am 30.07.2014 18:28, schrieb Al Kossow:
On 7/29/14 2:20 PM, Marco Rauhut wrote:
What do you want to say with IIRC ?
I see the input amplifier self oscillate if the remot/off/local
switch is in off position.
If i switch it to remote the output of the inplut amplifier go zero.
But on Interface cable i see some data (noise?) on the read lines.
How got the lines RD0, RD1, RD2, RTT and RMT to be if i have the pdp8
switched on and halted and the TU56 switched on and remote switch in
remote position. All lines 0V or all lines 5 V or the levels
jumping around?
There is positive feedback (R12) across the slicer op-amp. It is
supposed to oscillate when
the tape isn't moving.
If you've looked at the TC08 maint manual, you'll see that the G888's
weren't supposed to be
adjusted in the field.
If you have a second drive, swap G888's until you can isolate which
ones aren't working, then
try to find where (if) it starts working when you adjust the pot. The
best you can do then is find
the edge excursions where it stops working and center it.
Tuning beyond that gets into setting the clock, mark track, and data
tracks which
needs to be done with something more than the basic go/no go
performance diagnostic.
3581
days inactive
3582
days old
9 comments
3 participants
participants (3)
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aek＠bitsavers.org -
marco＠familie-rauhut.eu -
spacewar＠gmail.com