20 Sep
2011
20 Sep
'11
3:41 p.m.
Hi,
I'm trying to repair my RK05 drive. It seems that it doesn't find track 0
when loading the heads, thus moving the heads to the inner limit, forcing
a return-to-zero and starting all over again. I think the fault is on the
M7681 card (cylinder address and difference), the output of E16 pin 8
(CAD3 zero detect H) doesn't change, nor does the input on pin 10. And
here comes the problem: the M7681 isn't described in any DEC documentation
I've found so far (apart from the schematics), only the older M7702 card
(the function is practically the same, but they are completely different
designs). The new card contains several undocumented TTL ROMs (8223). The
output of pin 6 of E1 goes to the input pin 10 of E16, probably a
difference==zero bit.
So here comes my question: does anyone have a ROM listing of these ROMs,
especially of E1? I'd like to know what exactly that ROM is doing.
Christian
20 Sep
20 Sep
4:12 p.m.
Hi Christian,
Is the little red maintence switch in the right position? Was the
drive working earlier and just stopped? The quarterly PM usually helps
find this type of problem. Where are you located?
Paul
On Tue, Sep 20, 2011 at 2:41 PM, Christian Corti
<cc at informatik.uni-stuttgart.de> wrote:
Hi,
I'm trying to repair my RK05 drive. It seems that it doesn't find track 0
when loading the heads, thus moving the heads to the inner limit, forcing a
return-to-zero and starting all over again. I think the fault is on the
M7681 card (cylinder address and difference), the output of E16 pin 8 (CAD3
zero detect H) doesn't change, nor does the input on pin 10. And here comes
the problem: the M7681 isn't described in any DEC documentation I've found
so far (apart from the schematics), only the older M7702 card (the function
is practically the same, but they are completely different designs). The new
card contains several undocumented TTL ROMs (8223). The output of pin 6 of
E1 goes to the input pin 10 of E16, probably a difference==zero bit.
?So here comes my question: does anyone have a ROM listing of these ROMs,
especially of E1? I'd like to know what exactly that ROM is doing.
Christian
5:34 p.m.
On Tue, 20 Sep 2011, Paul Anderson wrote:
Is the little red maintence switch in the right
position? Was the
Yes, that switch simply disables the positioner current. I have it
disabled for the moment so that I can move the head assembly by hand and
observe the count pulses on the scope.
drive working earlier and just stopped? The quarterly
PM usually helps
find this type of problem. Where are you located?
Yes, the drive was working just fine. I think this is an electronics fault
on said card. Whatever I do I can observe changes on the DIFF outputs from
the ROM (outputs M0 to M4) but not on output M5. And the problem is that I
don't know when this output should go low.
I think I'll have to borrow another M7681 (and M7702 for reference) next
week from the spares of our museum (BTW I'm in Stuttgart, Germany).
Christian
21 Sep
21 Sep
1:41 p.m.
Yes, the drive was working just fine. I think this is
an electronics fault
on said card. Whatever I do I can observe changes on the DIFF outputs from
the ROM (outputs M0 to M4) but not on output M5. And the problem is that I
don't know when this output should go low.
A more general hint :
While individual bits of these bipolar PROMs can fail (in either
direction -- the fuses can 'grow back'), it's less common than failures
with the other circuitry in the device.
If you don't mind desoldering the ROM and reading it out, it's worth
checking for :
Stuck data bits (a data line which is 0 or 1 in all locations). If that
pin is conencted to other circuitry, it's a fair bet that it should
change sometimes
Address liens that do nothing. If the first half of the dump is the same
as the secodn ahlf, thena the MSB address inptu is not doign anything, if
the first had second quarters and the 3rd and 4th quarters are the same,
then the next addres line isn't doing anything, etc. If the address line
is driven by other circuity, it's a fair bet it should ahve some effect on
the output.
IF the dump apsses those 2 tests, it's quite likely the ROM is OK.
-tony
22 Sep
22 Sep
4:02 a.m.
On Wed, 21 Sep 2011, Tony Duell wrote:
While individual bits of these bipolar PROMs can fail
(in either
direction -- the fuses can 'grow back'), it's less common than failures
with the other circuitry in the device.
If you don't mind desoldering the ROM and reading it out, it's worth
checking for :
Stuck data bits (a data line which is 0 or 1 in all locations). If that
pin is conencted to other circuitry, it's a fair bet that it should
change sometimes
Address liens that do nothing. If the first half of the dump is the same
as the secodn ahlf, thena the MSB address inptu is not doign anything, if
the first had second quarters and the 3rd and 4th quarters are the same,
then the next addres line isn't doing anything, etc. If the address line
is driven by other circuity, it's a fair bet it should ahve some effect on
the output.
IF the dump apsses those 2 tests, it's quite likely the ROM is OK.
I had the same ideas yesterday. Thankfully the ROM is socketed, so I read
it out and found out its function and its fault. The function is more than
simple... it just inverts the inputs, i.e. output M0 is the inverse of the
address line A0. The sixth output M5 goes active (low) when all inputs are
low (zero difference detect). The fault was the A3 input. Therefore the
addresses x8-xF were mirrored at x0-x7, and the drive always assumed a
track difference of >= 8. Since I don't have a source of unused 32x8 bit
TTL ROMs, I've replaced the ROM with a GAL 16V8 (emulating the
open-collector behaviour) using a small adapter PCB.
For reference, here are the GAL equations:
; M7681 RK05 ROM 139A1 (position E1)
chip condcode gal16v8
; Pinbelegung:
; 1 2 3 4 5 6 7 8 9 10
nc nc /ENA /A4 /A3 /A2 /A1 /A0 nc gnd
; 11 12 13 14 15 16 17 18 19 20
nc nc nc D5 D4 D3 D2 D1 D0 vcc
equations
D0 = gnd
D1 = gnd
D2 = gnd
D3 = gnd
D4 = gnd
D5 = gnd
D0.oe = ENA & /A0
D1.oe = ENA & /A1
D2.oe = ENA & /A2
D3.oe = ENA & /A3
D4.oe = ENA & /A4
D5.oe = ENA & A0 & A1 & A2 & A3 & A4
Christian
10:17 a.m.
On 9/22/11 1:02 AM, Christian Corti wrote:
Since I don't have a source of unused 32x8 bit TTL
ROMs
http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_27844_-1
4:38 p.m.
I had the same ideas yesterday. Thankfully the ROM is
socketed, so I read
You were lucky. In one device I was working on recently, the microcode
ROMS were not only soldered directly to the PCB, there wasn't enough
headroom to put 2 of them in sockets. 3 of them went back in noraml
sockets, but the other 2 would have bnaged into the mains transformer.
Fortuantely, in this case the PCB holes were 1mm diameter so I could fit
some of those zero-height socket pins that go through the board.
it out and found out its function and its fault. The
function is more than
simple... it just inverts the inputs, i.e. output M0 is the inverse of the
I am sprised they used a ROM for that. Is the enable input used -- is there
some other open-colelctor output tied to the outputs of this ROM? If not,
you could do it i na copuple of TTL pacakges I think.
address line A0. The sixth output M5 goes active (low)
when all inputs are
low (zero difference detect). The fault was the A3 input. Therefore the
addresses x8-xF were mirrored at x0-x7, and the drive always assumed a
Right,... I'ev had several ICs fail with TTL inputs that appear to be
stuck high (as here) and the pin tests as a total open-circuit to the
power lines. I wonder if the failure is actually the bond-out wire
conencting the pin to the die, not the circuitry on the die itself. Not
that it really maters, I cna't rebond an IC here (yet!)
Do you know that it simply inverts the signals, or could it do soemthing
differnt for small cylinder offsets?
-tony
23 Sep
23 Sep
6:12 a.m.
On Thu, 22 Sep 2011, Tony Duell wrote:
You were lucky. In one device I was working on
recently, the microcode
Well, this particular ROM can be placed either in E1 (RK05J) or E2
(RK05F).
I am sprised they used a ROM for that. Is the enable
input used -- is there
some other open-colelctor output tied to the outputs of this ROM? If not,
you could do it i na copuple of TTL pacakges I think.
There are four ROMs on this board, they are used because this board can be
used in either a RK05J or RK05F (twice the number of cylinders). They use
the enable input as some kind of "seek enable" (called difference enable),
and the outputs are forced low with SN7416 drivers when the difference is
greater than 31 cylinders. The "value" from the ROM only determines the
seek speed profile, i.e. how fast the positioner will move the carriage.
Do you know that it simply inverts the signals, or
could it do soemthing
differnt for small cylinder offsets?
According to the schematics and the contents that I've read out of the ROM
it's nothing more. At least the drive works fine with this assumption. But
I'll read out an intact ROM if I can find one on another card.
Christian
21 Sep
21 Sep
1:11 p.m.
Hi Christian,
Is the little red maintence switch in the right position? Was the
I dont see how that could be the problem. The switch (on the servo power
amplifer board on top of the PSU) disables the positioner drive. If it's
in the wrong position, the heads won't move at all.
To the OP : Have you checked you're getting signals back from the optical
transducer on the positioner? Is the tranducer lamp glowing (they can
burn out)?
-tony
2:40 p.m.
On Wed, Sep 21, 2011 at 1:11 PM, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
To the OP : Have you checked you're getting
signals back from the optical
transducer on the positioner? Is the tranducer lamp glowing (they can
burn out)?
Back when I repaired them (1988), more than 50% of the units I worked
on had burned-out optical positioner lamps (and most of those, that
was the only part that needed replacing besides dirty filters). I
learned to power on the units and look down the open door - no light
meant I knew where to start.
-ethan
3:07 p.m.
Back when I repaired them (1988), more than 50% of the
units I worked
on had burned-out optical positioner lamps (and most of those, that
was the only part that needed replacing besides dirty filters). I
learned to power on the units and look down the open door - no light
meant I knew where to start.
And if you saw a flickering light from the rear right corner through the
door you powered down at once....
The blower fan runs off the mains, using the transformer primary winding
as an autotransformer on 230V mains. And it's on the 'hot' end of the
winding, so the fan motor's insulation has to withstand the full 230V.
Sometimes they don't and you get insulation breakdown. This starts as
sparka inaisw rhw motor, then the darn thing catches fire. Had to replace
a couple of those over the years...
-tony
4:39 p.m.
On Wed, Sep 21, 2011 at 3:07 PM, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
And if you saw a flickering light from the rear right
corner through the
door you powered down at once....
Never had one smoke (though we did nearly set off the halon from fried
rectifier diodes on an RK07 when one of the filtering caps went zero
ohms...
The blower fan runs off the mains, using the
transformer primary winding
as an autotransformer on 230V mains...
Sounds like a serious risk on your side of the pond, but here, inside small
kit we only push our electrons around half as hard. I won't say it can't
happen in the US, but ISTR mains wiring here is clad in plastic that
is rated to 600V.
-ethan
22 Sep
22 Sep
3:52 p.m.
On Wed, Sep 21, 2011 at 3:07 PM, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
My RK07s have been well-behaved (until now, lets hope it continues). I
did have a bridge rectifer go short-circuit all ways rounf in a 3rd part
(Plessay) Unibus expansion box. The wiring between it and the mains
transformer glowed red-hot and lost all its insulation (with lots of
magix smoke), but no other damage.
And if you saw a flickering light from the rear
right corner through the
door you powered down at once....
Never had one smoke (though we did nearly set off the halon from fried
rectifier diodes on an RK07 when one of the filtering caps went zero
ohms... The blower fan runs off the mains, using the
transformer primary winding
as an autotransformer on 230V mains...
Sounds like a serious risk on your side of the pond, but here, inside small
kit we only push our electrons around half as hard. I won't say it can't
happen in the US, but ISTR mains wiring here is clad in plastic that
is rated to 600V. 
23 Sep
23 Sep
4:39 a.m.
The blower fan runs off the mains, using the
transformer primary winding
as an autotransformer on 230V mains. And it's on the 'hot' end of the
winding, so the fan motor's insulation has to withstand the full 230V.
Sometimes they don't and you get insulation breakdown. This starts as
sparka inaisw rhw motor, then the darn thing catches fire. Had to replace
a couple of those over the years...
Hehe, I know that effect.. But no flames. Only sparks and a giving up
motor...
-- Ph
4660
days inactive
4663
days old
13 comments
6 participants
participants (6)
-
aek＠bitsavers.org -
ard＠p850ug1.demon.co.uk -
cc＠informatik.uni-stuttgart.de -
ethan.dicks＠gmail.com -
hachti＠hachti.de -
useddec＠gmail.com