10 Oct
2015
10 Oct
'15
2:15 a.m.
Once again, I find myself in over my head debugging a power supply, this
time an H7140 from a PDP-11/44. Here's the skinny:
That doesn't surprise me, the H7140 is one of the most complex PSUs you are
likely to come across...
When power is applied (plugged in, breaker switch
flipped to "On") the
relay does not click - based on my readings of the manuals this should
happen after the bias voltages are up to spec. I measure 308VDC on the
lugs on the top of the memory board, so that's at least something
working. Getting to other points to test voltages is a bit more
difficult, especially with those high voltages in the way, what a nice
design :).
That 300-odd volts comes from rectified (or voltage-doubled) mains. The
relay is part of the soft-start circuit, it should operate after the 'bias' PSU
has started up (it shorts out a resistor in the mains input circuit). With no
other load on the supply you will get the 300V with the resistor still in circuit.
There are _3_ SMPSUs in that box. One for the logic, one for the memory and
one (known as 'Bias' in the DEC documentation) to power the control circuits,
PSU control logic, etc. The last one is a relatively conventional SMPSU, it sounds
like it isn't working. It's nasty in that almost all the circuitry is on the mains
side of
the isolation barrier, and an isolating transformer is almost essential when working
on it. The chopper transformer is on the PSIU baseboard, the chopper transistor
and much of the control circuity is on the 'Bias/Interface' PCB (leftmost board in
the
PSU box). Be warned, therefore that some circuitry on this board is not isolated
from the mains.
I would start by seeing if the 12V (and 5V?) from the 'Bias supply' are missing.
-tony
10 Oct
10 Oct
8:18 a.m.
On Oct 10, 2015, at 2:15 AM, tony duell <ard at
p850ug1.demon.co.uk> wrote:
Thanks for the background and the tips, I?ll do some debugging. Any thoughts on the
?missing" diodes (D1-D4) on the bias board that I mentioned?
- Josh
Once again, I find myself in over my head debugging a power supply, this
time an H7140 from a PDP-11/44. Here's the skinny:
That doesn't surprise me, the H7140 is one of the most complex PSUs you are
likely to come across...
When power is applied (plugged in, breaker switch
flipped to "On") the
relay does not click - based on my readings of the manuals this should
happen after the bias voltages are up to spec. I measure 308VDC on the
lugs on the top of the memory board, so that's at least something
working. Getting to other points to test voltages is a bit more
difficult, especially with those high voltages in the way, what a nice
design :).
That 300-odd volts comes from rectified (or voltage-doubled) mains. The
relay is part of the soft-start circuit, it should operate after the 'bias' PSU
has started up (it shorts out a resistor in the mains input circuit). With no
other load on the supply you will get the 300V with the resistor still in circuit.
There are _3_ SMPSUs in that box. One for the logic, one for the memory and
one (known as 'Bias' in the DEC documentation) to power the control circuits,
PSU control logic, etc. The last one is a relatively conventional SMPSU, it sounds
like it isn't working. It's nasty in that almost all the circuitry is on the
mains side of
the isolation barrier, and an isolating transformer is almost essential when working
on it. The chopper transformer is on the PSIU baseboard, the chopper transistor
and much of the control circuity is on the 'Bias/Interface' PCB (leftmost board
in the
PSU box). Be warned, therefore that some circuitry on this board is not isolated
from the mains.
I would start by seeing if the 12V (and 5V?) from the 'Bias supply' are missing.
-tony
10:32 a.m.
l?rdag 10 oktober 2015 skrev Josh Dersch <derschjo at gmail.com>:
are
Thanks for the background and the tips, I?ll do some debugging. Any
thoughts on the ?missing" diodes (D1-D4) on the bias board that I mentioned?
From a quick glance at the schematic I think that this part is related to the fan
driving circuitry. The diodes look like some kind of protection
diodes which is good to have when switching inductive loads. I have really
no idea why they have been removed. But I don't think it is related to the
PSU not working at all.
/Mattis
On Oct 10, 2015, at 2:15 AM, tony duell <ard
at p850ug1.demon.co.uk
<javascript:;>> wrote:
Once again, I find myself in over my head debugging a power supply, this
time an H7140 from a PDP-11/44. Here's the skinny:
That doesn't surprise me, the H7140 is one of the most complex PSUs you likely to come across...
'bias' PSU
When power is applied (plugged in, breaker switch
flipped to "On") the
relay does not click - based on my readings of the manuals this should
happen after the bias voltages are up to spec. I measure 308VDC on the
lugs on the top of the memory board, so that's at least something
working. Getting to other points to test voltages is a bit more
difficult, especially with those high voltages in the way, what a nice
design :).
That 300-odd volts comes from rectified (or voltage-doubled) mains. The
relay is part of the soft-start circuit, it should operate after the has started up (it shorts out a resistor in the
mains input circuit).
With no
other load on the supply you will get the 300V
with the resistor still
in circuit.
There are _3_ SMPSUs in that box. One for the logic, one for the memory
and
one (known as 'Bias' in the DEC
documentation) to power the control
circuits,
PSU control logic, etc. The last one is a
relatively conventional SMPSU,
it sounds
like it isn't working. It's nasty in that
almost all the circuitry is on
the mains side of
the isolation barrier, and an isolating
transformer is almost essential
when working
on it. The chopper transformer is on the PSIU
baseboard, the chopper
transistor
and much of the control circuity is on the
'Bias/Interface' PCB
(leftmost board in the
PSU box). Be warned, therefore that some
circuitry on this board is not
isolated
from the mains.
I would start by seeing if the 12V (and 5V?) from the 'Bias supply' are
missing.
- Josh
-tony
2:38 p.m.
From a quick glance at the schematic I think that this part is related to
the fan driving circuitry. The diodes look like some kind of protection
Yes.
diodes which is good to have when switching inductive
loads. I have really
no idea why they have been removed. But I don't think it is related to the
Remember that said diodes do slow down the decay of the current (and thus
the magnetic field) when the transistor turns off (this can be a problem with
solenoid drivers for paper tape punches, etc). It is possible that with the diodes
in-circuit the fan drive waveforms were not right.
PSU not working at all.
Correct. The fan driver is powered by the 36V output of the 'memory' SMPSU,
Even if it is defective, the bias supply should run, the logic supplies should come
up in the ON position of the key, and so on.
That 'bias/interface' PCB contains (at least) the bias supply chopper and control
circuit; the fan driver; and the control logic to start the 2 main PSUs in the correct
posiitions of the keyswitch,
-tony
/Mattis
- Josh
-tony
8:44 p.m.
On Sat, Oct 10, 2015 at 2:38 PM, tony duell <ard at p850ug1.demon.co.uk> wrote:
Thanks for the explanation. I tacked on some wires to the bias board (to
bring them out for safe probing); the wires are connected to the 5V logic
supply and the +12V bias supply and I get nothing at all out of them when
the H7140 is turned on.
I'm slowly coming to terms with the schematic but I'm not quite clear where
these two voltages are being generated. I note from the block diagram that
the +15 and +12 are rectified on the motherboard (backplane) -- which
should make it GREAT fun to probe. So it looks like some careful
disassembly is now required (unless there's a trick to probing things on
the backplane...)
Thanks,
Josh
From a quick glance at the schematic I think that this part is related to
the fan driving circuitry. The diodes look like some kind of protection
Yes.
diodes which is good to have when switching
inductive loads. I have
really
no idea why they have been removed. But I
don't think it is related to
the
Remember that said diodes do slow down the decay of the current (and thus
the magnetic field) when the transistor turns off (this can be a problem
with
solenoid drivers for paper tape punches, etc). It is possible that with
the diodes
in-circuit the fan drive waveforms were not right.
PSU not working at all.
Correct. The fan driver is powered by the 36V output of the 'memory' SMPSU,
Even if it is defective, the bias supply should run, the logic supplies
should come
up in the ON position of the key, and so on.
That 'bias/interface' PCB contains (at least) the bias supply chopper and
control
circuit; the fan driver; and the control logic to start the 2 main PSUs in
the correct
posiitions of the keyswitch,
-tony
/Mattis
- Josh
-tony
8:46 p.m.
On Sat, Oct 10, 2015 at 8:44 PM, Josh Dersch <derschjo at gmail.com> wrote:
On Sat, Oct 10, 2015 at 2:38 PM, tony duell <ard at
p850ug1.demon.co.uk>
wrote:
Thanks for the explanation. I tacked on some wires to the bias board (to
bring them out for safe probing); the wires are connected to the 5V logic
supply and the +12V bias supply and I get nothing at all out of them when
the H7140 is turned on.
I'm slowly coming to terms with the schematic but I'm not quite clear
where these two voltages are being generated. I note from the block
diagram that the +15 and +12 are rectified on the motherboard (backplane)
-- which should make it GREAT fun to probe. So it looks like some careful
disassembly is now required (unless there's a trick to probing things on
the backplane...)
Thanks,
Josh
And a quick correction, it's -15V, not +15; I need to proofread more :)
- Josh
From a quick glance at the schematic I think that this part is related
to
the fan driving circuitry. The diodes look like
some kind of protection
Yes.
diodes which is good to have when switching
inductive loads. I have
really
no idea why they have been removed. But I
don't think it is related to
the
Remember that said diodes do slow down the decay of the current (and thus
the magnetic field) when the transistor turns off (this can be a problem
with
solenoid drivers for paper tape punches, etc). It is possible that with
the diodes
in-circuit the fan drive waveforms were not right.
PSU not working at all.
Correct. The fan driver is powered by the 36V output of the 'memory'
SMPSU,
Even if it is defective, the bias supply should run, the logic supplies
should come
up in the ON position of the key, and so on.
That 'bias/interface' PCB contains (at least) the bias supply chopper and
control
circuit; the fan driver; and the control logic to start the 2 main PSUs
in the correct
posiitions of the keyswitch,
-tony
/Mattis
- Josh
-tony
11 Oct
11 Oct
12:02 a.m.
2015-10-11 5:44 GMT+02:00 Josh Dersch <derschjo at gmail.com>:
On Sat, Oct 10, 2015 at 2:38 PM, tony duell <ard at
p850ug1.demon.co.uk>
wrote:
SMPSU,
Then I would check the circuitry on page 3 of the schematic on the bias
board. Use a insulation transformer (and possibly a variac) and check
voltages here. Does the 555 has supply voltage?
Does the 16.5V zener operate correctly? Is Q6 ok? If yes, is there a
waveform on 3 of the 555? What is the signal like on base Q1? Collector Q1?
(probably nothing since you don't have any bias voltage)
>
> From a quick glance at the schematic I think that this part is related
to
the fan
driving circuitry. The diodes look like some kind of protection
Yes.
diodes which is good to have when switching
inductive loads. I have
really
no idea why they have been removed. But I
don't think it is related to
the
Remember that said diodes do slow down the decay of the current (and thus
the magnetic field) when the transistor turns off (this can be a problem
with
solenoid drivers for paper tape punches, etc). It is possible that with
the diodes
in-circuit the fan drive waveforms were not right.
PSU not working at all.
Correct. The fan driver is powered by the 36V output of the 'memory' Even if it is defective, the bias supply should
run, the logic supplies
should come
up in the ON position of the key, and so on.
That 'bias/interface' PCB contains (at least) the bias supply chopper and
control
circuit; the fan driver; and the control logic to start the 2 main PSUs
in
the correct
posiitions of the keyswitch,
-tony
/Mattis
Thanks for the explanation. I tacked on some wires to the bias board (to
bring them out for safe probing); the wires are connected to the 5V logic
supply and the +12V bias supply and I get nothing at all out of them when
the H7140 is turned on.
- Josh
-tony
I'm slowly coming to terms with the schematic but
I'm not quite clear where
these two voltages are being generated. I note from the block diagram that
the +15 and +12 are rectified on the motherboard (backplane) -- which
should make it GREAT fun to probe. So it looks like some careful
disassembly is now required (unless there's a trick to probing things on
the backplane...)
The bias voltage is generated by the chopper on page three in conjunction
with T1 and some rectifying diodes on the motherboard. Then it is feed back
to the bias board on J2:2 to produce the 5V. (page 2)
Good luck!
Thanks,
Josh
10:17 a.m.
The bias voltage is generated by the chopper on page three in conjunction
with T1 and some rectifying diodes on the motherboard. Then it is feed back
to the bias board on J2:2 to produce the 5V. (page 2)
Yes...
It's not totally obvious at first glance, but this is yet another SMPSU with the
chopper on the Bias/Interface board. The transformer on the baseboard is
not a mains-frequency one.
-tony
10:23 a.m.
I'm slowly coming to terms with the schematic but I'm not quite clear where
these two voltages are being generated. I note from the block diagram that
the +15 and +12 are rectified on the motherboard (backplane) -- which
should make it GREAT fun to probe. So it looks like some careful
disassembly is now required (unless there's a trick to probing things on
the backplane...)
I will give page references as for the .pdf of the printset on bitsavers.
The bias supply is a switcher. On page 162, T1 is the chopper transformer,
D6 the output-side rectifier, C3 the smoothing capacitor
On page 168 (Bias/Interface PCB) Q1 is the chopper transistor, E2 (555) the
control oscillator, etc.
E1 on page 167 produces 5V from the 12V supply, but if the latter is missing it
can't do a lot. Get the 12V back first.
-tony
12:07 p.m.
On 2015-Oct-10, at 8:44 PM, Josh Dersch wrote:
. . .
Thanks for the explanation. I tacked on some wires to
the bias board (to
bring them out for safe probing); the wires are connected to the 5V logic
supply and the +12V bias supply and I get nothing at all out of them when
the H7140 is turned on.
I'm slowly coming to terms with the schematic but I'm not quite clear where
these two voltages are being generated. I note from the block diagram that
the +15 and +12 are rectified on the motherboard (backplane) -- which
should make it GREAT fun to probe. So it looks like some careful
disassembly is now required (unless there's a trick to probing things on
the backplane...)
Note that the "+13V" supply must also be present, and it's generated and
referenced on the Mains side of everything.
In summary, for the relay to activate:
1) The Mains is rectified and filtered to produce Mains +300V via bridge LNS-CR1 and caps
LNS-C1,C2.
2) MOB-D1,D2,R1,R2 form a voltage divider / balancing network to produce Mains +150VDC.
They also balance the voltage across the Mains filter caps (LNS-C1,C2) when in 220VAC
mode.
** 3) Mains +150V is regulated via MOB-R3, BIB-Q6, BIB-C4, BIB-D11 to produce Mains +13V,
referenced
from MOB-D2 feeding ("START-UP DRIVE") the base of BIB-Q6.
16V zener BIB-D12 additionally clamps this level.
4) Mains +13V supplies 555 oscillator BIB-E2, LM393 comparator BIB-E3b and associated
circuitry. These form a SMPSU with MOB-T1.
5) The output from MOB-T1 is half-wave rectified in both polarities to produce BIB +12V
(MOB-D6,C3) and BIB -15V (MOB-R4,R5,R6,D4,C2,D5).
6) BIB +12V produces BIB +5V via regulator BIB-E1.
7) BIB-E3a forms a voltage level sensor with reference zener BIB-D13 and voltage divider
BIB-R3,R4,R27 that must detect an adequate level on
the Mains +300V to turn on the relay via BIB-Q11, BIB-E5, BIB-E4a.
LNS = Line Supply section PDF.146
MOB = Motherboard PDF.162
BIB = Bias & Interface Board PDF.166-168
** There appears to be something inconsistent in the schematic here in that the base of
BIB-Q6 is fed by +10V from MOB-D2, which would leave the Mains +13V at more like +8V.
Am I missing something? - is there anywhere in that doc that explicitly declares the
association between the 2-dozen connectors, for example, that Line Supply P1 & P2
connect to Motherboard J5 & J4, and that Bias and Interface Board J1 & J2 connect
to Motherboard J7 & J6?
12:26 p.m.
Am I missing something? - is there anywhere in that doc that explicitly declares the
association between the 2-dozen connectors, for example, that Line Supply P1 & P2
connect to Motherboard J5 & J4, and that Bias and Interface Board J1 & J2
connect
to Motherboard J7 & J6?
Not that I can see. DEC were not good about providing things like that. Sometimes there
would be a cabling diagram in the maintenance manual as opposed to the printset, but
not always.
I suppose if you have the unit in front of you it is obvious what is plugged into what,
but
I would still expect a diagram in the manual.
-tony
12:57 p.m.
2015-10-11 21:07 GMT+02:00 Brent Hilpert <hilpert at cs.ubc.ca>:
On 2015-Oct-10, at 8:44 PM, Josh Dersch wrote:
. . .
Very nice and clear description on what is required to have relay to
activate!
Thanks for the explanation. I tacked on some
wires to the bias board (to
bring them out for safe probing); the wires are connected to the 5V logic
supply and the +12V bias supply and I get nothing at all out of them when
the H7140 is turned on.
I'm slowly coming to terms with the schematic but I'm not quite clear
where
these two voltages are being generated. I note
from the block diagram
that
the +15 and +12 are rectified on the motherboard
(backplane) -- which
should make it GREAT fun to probe. So it looks like some careful
disassembly is now required (unless there's a trick to probing things on
the backplane...)
Note that the "+13V" supply must also be present, and it's generated and
referenced on the Mains side of everything.
In summary, for the relay to activate:
1) The Mains is rectified and filtered to produce Mains +300V via
bridge LNS-CR1 and caps LNS-C1,C2.
2) MOB-D1,D2,R1,R2 form a voltage divider / balancing network to
produce Mains +150VDC.
They also balance the voltage across the Mains filter caps
(LNS-C1,C2) when in 220VAC mode.
** 3) Mains +150V is regulated via MOB-R3, BIB-Q6, BIB-C4, BIB-D11 to
produce Mains +13V, referenced
from MOB-D2 feeding ("START-UP DRIVE") the base of BIB-Q6.
16V zener BIB-D12 additionally clamps this level.
4) Mains +13V supplies 555 oscillator BIB-E2, LM393 comparator
BIB-E3b and associated circuitry. These form a SMPSU with MOB-T1.
5) The output from MOB-T1 is half-wave rectified in both
polarities to produce BIB +12V (MOB-D6,C3) and BIB -15V
(MOB-R4,R5,R6,D4,C2,D5).
6) BIB +12V produces BIB +5V via regulator BIB-E1.
7) BIB-E3a forms a voltage level sensor with reference zener
BIB-D13 and voltage divider BIB-R3,R4,R27 that must detect an adequate
level on
the Mains +300V to turn on the relay via BIB-Q11, BIB-E5,
BIB-E4a.
LNS = Line Supply section PDF.146
MOB = Motherboard PDF.162
BIB = Bias & Interface Board PDF.166-168
** There appears to be something inconsistent in the schematic here in
that the base of BIB-Q6 is fed by +10V from MOB-D2, which would leave the
Mains +13V at more like +8V.
Am I missing something? - is there anywhere in that doc that explicitly
declares the association between the 2-dozen connectors, for example, that
Line Supply P1 & P2 connect to Motherboard J5 & J4, and that Bias and
Interface Board J1 & J2 connect to Motherboard J7 & J6?
Not in the FMPS as far as I can see. But the BA11-A Technical Manual has a
nice figure 3-2 (page 3-5) which associate various connectors in the PSU.
6:19 p.m.
On Sun, Oct 11, 2015 at 12:07 PM, Brent Hilpert <hilpert at cs.ubc.ca> wrote:
On 2015-Oct-10, at 8:44 PM, Josh Dersch wrote:
. . .
Awesome, thanks for the detailed writeup. Things make sense, or at least
more sense.
I went to take a look at the +13V supply and of *course* once I did things
started working, mysteriously. The relay clicks over and I get +13V and it
looks like the bias voltages are present as well. All I did was tack on a
wire to the 10/L header pins on the bias/interface board (+13V)...
So that's... good, but I have no idea what the actual problem is/was.
Going to clean the connectors and look for cold solder joints (again :))
just to rule that out. I'll get a dummy load hooked up and see if anything
happens when I throw the front panel switch.
Thanks again, all.
- Josh
Thanks for the explanation. I tacked on some
wires to the bias board (to
bring them out for safe probing); the wires are connected to the 5V logic
supply and the +12V bias supply and I get nothing at all out of them when
the H7140 is turned on.
I'm slowly coming to terms with the schematic but I'm not quite clear
where
these two voltages are being generated. I note
from the block diagram
that
the +15 and +12 are rectified on the motherboard
(backplane) -- which
should make it GREAT fun to probe. So it looks like some careful
disassembly is now required (unless there's a trick to probing things on
the backplane...)
Note that the "+13V" supply must also be present, and it's generated and
referenced on the Mains side of everything.
In summary, for the relay to activate:
1) The Mains is rectified and filtered to produce Mains +300V via
bridge LNS-CR1 and caps LNS-C1,C2.
2) MOB-D1,D2,R1,R2 form a voltage divider / balancing network to
produce Mains +150VDC.
They also balance the voltage across the Mains filter caps
(LNS-C1,C2) when in 220VAC mode.
** 3) Mains +150V is regulated via MOB-R3, BIB-Q6, BIB-C4, BIB-D11 to
produce Mains +13V, referenced
from MOB-D2 feeding ("START-UP DRIVE") the base of BIB-Q6.
16V zener BIB-D12 additionally clamps this level.
4) Mains +13V supplies 555 oscillator BIB-E2, LM393 comparator
BIB-E3b and associated circuitry. These form a SMPSU with MOB-T1.
5) The output from MOB-T1 is half-wave rectified in both
polarities to produce BIB +12V (MOB-D6,C3) and BIB -15V
(MOB-R4,R5,R6,D4,C2,D5).
6) BIB +12V produces BIB +5V via regulator BIB-E1.
7) BIB-E3a forms a voltage level sensor with reference zener
BIB-D13 and voltage divider BIB-R3,R4,R27 that must detect an adequate
level on
the Mains +300V to turn on the relay via BIB-Q11, BIB-E5,
BIB-E4a.
LNS = Line Supply section PDF.146
MOB = Motherboard PDF.162
BIB = Bias & Interface Board PDF.166-168
** There appears to be something inconsistent in the schematic here in
that the base of BIB-Q6 is fed by +10V from MOB-D2, which would leave the
Mains +13V at more like +8V.
Am I missing something? - is there anywhere in that doc that explicitly
declares the association between the 2-dozen connectors, for example, that
Line Supply P1 & P2 connect to Motherboard J5 & J4, and that Bias and
Interface Board J1 & J2 connect to Motherboard J7 & J6?
8:01 p.m.
On 10/11/15 6:19 PM, Josh Dersch wrote:
On Sun, Oct 11, 2015 at 12:07 PM, Brent Hilpert
<hilpert at cs.ubc.ca
<mailto:hilpert at cs.ubc.ca>> wrote:
On 2015-Oct-10, at 8:44 PM, Josh Dersch wrote:
. . .
Note that the "+13V" supply must also be present, and it's
generated and referenced on the Mains side of everything.
In summary, for the relay to activate:
1) The Mains is rectified and filtered to produce Mains
+300V via bridge LNS-CR1 and caps LNS-C1,C2.
2) MOB-D1,D2,R1,R2 form a voltage divider / balancing
network to produce Mains +150VDC.
They also balance the voltage across the Mains filter
caps (LNS-C1,C2) when in 220VAC mode.
** 3) Mains +150V is regulated via MOB-R3, BIB-Q6, BIB-C4,
BIB-D11 to produce Mains +13V, referenced
from MOB-D2 feeding ("START-UP DRIVE") the base of BIB-Q6.
16V zener BIB-D12 additionally clamps this level.
4) Mains +13V supplies 555 oscillator BIB-E2, LM393
comparator BIB-E3b and associated circuitry. These form a SMPSU
with MOB-T1.
5) The output from MOB-T1 is half-wave rectified in both
polarities to produce BIB +12V (MOB-D6,C3) and BIB -15V
(MOB-R4,R5,R6,D4,C2,D5).
6) BIB +12V produces BIB +5V via regulator BIB-E1.
7) BIB-E3a forms a voltage level sensor with reference
zener BIB-D13 and voltage divider BIB-R3,R4,R27 that must detect
an adequate level on
the Mains +300V to turn on the relay via BIB-Q11,
BIB-E5, BIB-E4a.
LNS = Line Supply section PDF.146
MOB = Motherboard PDF.162
BIB = Bias & Interface Board PDF.166-168
** There appears to be something inconsistent in the schematic
here in that the base of BIB-Q6 is fed by +10V from MOB-D2, which
would leave the Mains +13V at more like +8V.
Am I missing something? - is there anywhere in that doc that
explicitly declares the association between the 2-dozen
connectors, for example, that Line Supply P1 & P2 connect to
Motherboard J5 & J4, and that Bias and Interface Board J1 & J2
connect to Motherboard J7 & J6?
Awesome, thanks for the detailed writeup. Things make sense, or at
least more sense.
I went to take a look at the +13V supply and of *course* once I did
things started working, mysteriously. The relay clicks over and I get
+13V and it looks like the bias voltages are present as well. All I
did was tack on a wire to the 10/L header pins on the bias/interface
board (+13V)...
So that's... good, but I have no idea what the actual problem is/was.
Going to clean the connectors and look for cold solder joints (again
:)) just to rule that out. I'll get a dummy load hooked up and see if
anything happens when I throw the front panel switch.
Thanks again, all.
- Josh
Re-inspection revealed no cold solder joints, but I reflowed the
backplane connector pins on the Bias/Interface board pins L and 10
anyway. I reassembled everything in the chassis, hooked up a dummy load
and everything came up fine. Reinstalled the CPU boardset + terminator
and I get the Console chevron prompt after a couple of seconds and the
built-in diagnostic tests pass. So, success, of a sort. I feel like I
cheated somehow :). We'll see if it keeps working...
Now to figure out mass storage; I have an SMD controller and a drive --
let's find out if either of them work :).
Thanks again for the analysis and advice, I'm slowly figuring things out
but I think I really need to sit down one of these days and really study
power supply electronics.
- Josh
3311
days inactive
3313
days old
13 comments
4 participants
participants (4)
-
ard＠p850ug1.demon.co.uk -
derschjo＠gmail.com -
hilpert＠cs.ubc.ca -
mattislind＠gmail.com