17 Mar
2016
17 Mar
'16
3:34 p.m.
Hi all --
Yesterday I replaced the dead 2N6547 transistor in the H7104 and fired
'er up again. Same exact results. (The timbre of the power supply
whine may have changed slightly, it's hard to tell). So, back to the
drawing board. I tested the replacement transistor after power-up and
it was still good, so at least it wasn't a casualty.
On closer inspection, I found what appears to be a large-ish (maybe
2.5-3mm in diameter) resistor with a hairline crack down the middle.
Testing reveals it to be open-circuit, and looking at the print set
reveals it to be connected to a leg of the transistor I just replaced,
so that seems suspect. I noted no smoke or odor during any of the times
I've powered this thing up (the resistor is on the outside edge of the
supply and I was watching pretty closely at all times) so I assume it
was dead long before I got ahold of this machine and I just overlooked it.
It's listed in the print set as a 1 Ohm, 2 Watt resistor, with a "FUSE"
designation. I'm not entirely sure what I should be searching for for a
replacement; clearly the "fuse" part of the designation is important but
I'm not sure what a modern equivalent is. I've browsed around Mouser
for awhile and I'm not seeing anything obvious. I'm sure this is
obvious to anyone with experience -- can you point me in the right
direction?
Thanks,
Josh
17 Mar
17 Mar
3:46 p.m.
From: Josh Dersch: Thursday, March 17, 2016 3:34 PM
It's listed in the print set as a 1 Ohm, 2 Watt
resistor, with a "FUSE"
designation. I'm not entirely sure what I should be searching for for a
replacement; clearly the "fuse" part of the designation is important but
I'm not sure what a modern equivalent is. I've browsed around Mouser
for awhile and I'm not seeing anything obvious. I'm sure this is
obvious to anyone with experience -- can you point me in the right
direction?
There was a recent discussion here about a similar component in
a VT100 supply. I think a suitable replacement was eventually found
at Farnell/Newark.
Vince
5:44 p.m.
On 17/03/2016 22:46, "Vincent Slyngstad" <v.slyngstad at frontier.com>
wrote:
From: Josh Dersch: Thursday, March 17, 2016 3:34 PM
Yep, that was me looking for the same part. Does yours look like this?
http://f0p.co.uk/r22.jpg
According to Onecall Farnell 'a blue band at position 5 indicates 20%
tolerance' which would make it a tolerance multiplier of 2.
However the only ones they sell are 5% tolerance, ie brown-black-gold-gold
not brown-black-gold-silver + blue, but the technical chap I spoke to seemed
certain these would be ok. I bought 5 just in case.
Onecall are education-only suppliers but the same part numbers work with
Farnell/Element14. Part# is 1692450.
--
Adrian/Witchy
Binary Dinosaurs creator/curator
Www.binarydinosaurs.co.uk - the UK's biggest private home computer
collection?
It's listed in the print set as a 1 Ohm, 2
Watt resistor, with a "FUSE"
designation. I'm not entirely sure what I should be searching for for a
replacement; clearly the "fuse" part of the designation is important but
I'm not sure what a modern equivalent is. I've browsed around Mouser
for awhile and I'm not seeing anything obvious. I'm sure this is
obvious to anyone with experience -- can you point me in the right
direction?
There was a recent discussion here about a similar component in
a VT100 supply. I think a suitable replacement was eventually found
at Farnell/Newark. 
6:54 p.m.
Glad this came back up.
Was any consensus achieved, regarding the use of `flameproof` resistor
types as direct substitutes for designated "fusible resistors"?
On Thu, Mar 17, 2016 at 7:44 PM, Adrian Graham <witchy at binarydinosaurs.co.uk
wrote:
> On 17/03/2016 22:46, "Vincent Slyngstad" <v.slyngstad at
frontier.com wrote:
>
> > From: Josh Dersch: Thursday, March 17, 2016 3:34 PM
> >> It's listed in the print set as a 1 Ohm, 2 Watt resistor, with a
"FUSE"
> >> designation. I'm not entirely sure what I should be searching for for
a
> >> replacement; clearly the "fuse" part of the designation is
important but
> >> I'm not sure what a modern equivalent is. I've browsed around
Mouser
> >> for awhile and I'm not seeing anything obvious. I'm sure this is
> >> obvious to anyone with experience -- can you point me in the right
> >> direction?
> >
> > There was a recent discussion here about a similar component in
> > a VT100 supply. I think a suitable replacement was eventually found
> > at Farnell/Newark.
>
> Yep, that was me looking for the same part. Does yours look like this?
>
> http://f0p.co.uk/r22.jpg
>
> According to Onecall Farnell 'a blue band at position 5 indicates 20%
> tolerance' which would make it a tolerance multiplier of 2.
>
> However the only ones they sell are 5% tolerance, ie brown-black-gold-gold
> not brown-black-gold-silver + blue, but the technical chap I spoke to
> seemed
> certain these would be ok. I bought 5 just in case.
>
> Onecall are education-only suppliers but the same part numbers work with
> Farnell/Element14. Part# is 1692450.
>
> --
> Adrian/Witchy
> Binary Dinosaurs creator/curator
> Www.binarydinosaurs.co.uk - the UK's biggest private home computer
> collection?
>
>
>
7:11 p.m.
On 3/17/16 5:44 PM, Adrian Graham wrote:
On 17/03/2016 22:46, "Vincent Slyngstad"
<v.slyngstad at frontier.com> wrote:
Thanks! Yes, that looks very similar except mine has a tolerance rating
of 10%. Vincent helpfully pointed me at:
http://www.digikey.com/product-detail/en/tt-electronics-irc/SPP2UL1R00JLF/9…
which look like they should do the job, and I ordered a handful just in
case I ever need a few more.
Thanks again,
Josh
From: Josh Dersch: Thursday, March 17, 2016 3:34
PM
Yep, that was me looking for the same part. Does yours look
like this?
http://f0p.co.uk/r22.jpg
According to Onecall Farnell 'a blue band at position 5 indicates 20%
tolerance' which would make it a tolerance multiplier of 2.
However the only ones they sell are 5% tolerance, ie brown-black-gold-gold
not brown-black-gold-silver + blue, but the technical chap I spoke to seemed
certain these would be ok. I bought 5 just in case.
Onecall are education-only suppliers but the same part numbers work with
Farnell/Element14. Part# is 1692450.
It's listed in the print set as a 1 Ohm, 2
Watt resistor, with a "FUSE"
designation. I'm not entirely sure what I should be searching for for a
replacement; clearly the "fuse" part of the designation is important but
I'm not sure what a modern equivalent is. I've browsed around Mouser
for awhile and I'm not seeing anything obvious. I'm sure this is
obvious to anyone with experience -- can you point me in the right
direction?
There was a recent discussion here about a similar component in
a VT100 supply. I think a suitable replacement was eventually found
at Farnell/Newark.
18 Mar
18 Mar
2:27 a.m.
On 18/03/2016 02:11, "Josh Dersch" <derschjo at gmail.com> wrote:
I'll be adding mine tonight or tomorrow so if the smoke escapes I'll get
some of those, why they didn't come up on my search for 'fusible resistor'
I'll never know.
--
Adrian/Witchy
Binary Dinosaurs creator/curator
Www.binarydinosaurs.co.uk - the UK's biggest private home computer
collection?
However the
only ones they sell are 5% tolerance, ie brown-black-gold-gold
not brown-black-gold-silver + blue, but the technical chap I spoke to seemed
certain these would be ok. I bought 5 just in case.
Onecall are education-only suppliers but the same part numbers work with
Farnell/Element14. Part# is 1692450.
Thanks! Yes, that looks very similar except mine has a tolerance rating
of 10%. Vincent helpfully pointed me at:
http://www.digikey.com/product-detail/en/tt-electronics-irc/SPP2UL1R00JLF/9…
1272-1-ND/4215463
which look like they should do the job, and I ordered a handful just in
case I ever need a few more.
21 Mar
21 Mar
12:53 p.m.
On 18/03/2016 02:11, "Josh Dersch" <derschjo at gmail.com> wrote:
Good news - mine worked so fingers crossed for yours too. I now have a
functioning PSU again though I've not tried it back in the chassis yet...
--
Adrian/Witchy
Binary Dinosaurs creator/curator
Www.binarydinosaurs.co.uk - the UK's biggest private home computer
collection?
Onecall are
education-only suppliers but the same part numbers work with
Farnell/Element14. Part# is 1692450.
Thanks! Yes, that looks very similar except mine has a tolerance rating
of 10%. Vincent helpfully pointed me at:
http://www.digikey.com/product-detail/en/tt-electronics-irc/SPP2UL1R00JLF/9…
1272-1-ND/4215463
which look like they should do the job, and I ordered a handful just in
case I ever need a few more.
6:50 p.m.
I don't quite get what makes this DigiKey part suitable for the role of a
fused resistor. I do see that it has specs for 'fusing behavior' but that
aside, I don't see that this series is marketed / sold as a "fusible
resistor".
One reason I question it, is the fact that the fusing ratings are only
plotted for like 40X or 50X expected current. Can the circuit under
protection be relied upon to produce those levels of current, even under
hard-fault conditions?
Always trying to learn..
On Mon, Mar 21, 2016 at 2:53 PM, Adrian Graham <witchy at binarydinosaurs.co.uk
wrote:
> On 18/03/2016 02:11, "Josh Dersch" <derschjo at gmail.com wrote:
>
> >> Onecall are education-only suppliers but the same part numbers work with
> >> Farnell/Element14. Part# is 1692450.
> >>
> >
> > Thanks! Yes, that looks very similar except mine has a tolerance rating
> > of 10%. Vincent helpfully pointed me at:
> >
> >
> http://www.digikey.com/product-detail/en/tt-electronics-irc/SPP2UL1R00JLF/9…
> > 1272-1-ND/4215463
> >
> > which look like they should do the job, and I ordered a handful just in
> > case I ever need a few more.
>
> Good news - mine worked so fingers crossed for yours too. I now have a
> functioning PSU again though I've not tried it back in the chassis yet...
>
> --
> Adrian/Witchy
> Binary Dinosaurs creator/curator
> Www.binarydinosaurs.co.uk - the UK's biggest private home computer
> collection?
>
>
>
7:34 p.m.
Maybe a real fuse in series with a real resistor.
Dwight
________________________________________
From: cctalk <cctalk-bounces at classiccmp.org> on behalf of drlegendre .
<drlegendre at gmail.com>
Sent: Monday, March 21, 2016 6:50 PM
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Re: Resistor/Fuse replacement (DEC H7104-D)
I don't quite get what makes this DigiKey part suitable for the role of a
fused resistor. I do see that it has specs for 'fusing behavior' but that
aside, I don't see that this series is marketed / sold as a "fusible
resistor".
One reason I question it, is the fact that the fusing ratings are only
plotted for like 40X or 50X expected current. Can the circuit under
protection be relied upon to produce those levels of current, even under
hard-fault conditions?
Always trying to learn..
On Mon, Mar 21, 2016 at 2:53 PM, Adrian Graham <witchy at binarydinosaurs.co.uk
wrote:
> On 18/03/2016 02:11, "Josh Dersch" <derschjo at gmail.com wrote:
>
> >> Onecall are education-only suppliers but the same part numbers work with
> >> Farnell/Element14. Part# is 1692450.
> >>
> >
> > Thanks! Yes, that looks very similar except mine has a tolerance rating
> > of 10%. Vincent helpfully pointed me at:
> >
> >
> http://www.digikey.com/product-detail/en/tt-electronics-irc/SPP2UL1R00JLF/9…
> > 1272-1-ND/4215463
> >
> > which look like they should do the job, and I ordered a handful just in
> > case I ever need a few more.
>
> Good news - mine worked so fingers crossed for yours too. I now have a
> functioning PSU again though I've not tried it back in the chassis yet...
>
> --
> Adrian/Witchy
> Binary Dinosaurs creator/curator
> Www.binarydinosaurs.co.uk - the UK's biggest private home computer
> collection?
>
>
>
8:44 p.m.
On 03/21/2016 07:34 PM, dwight wrote:
Maybe a real fuse in series with a real resistor.
I'd asked that, but reconsidered in that fusible resistors all seem to
have a strong positive temperature coefficient and then a point at which
they will fuse.
IOW, the things degrade gradually before going ka-pow; something not
realized with a resistor+fuse combination.
See, for example:
http://www.vishay.com/docs/28737/nfr25.pdf
--Chuck
22 Mar
22 Mar
8:20 a.m.
From: drlegendre: Monday, March 21, 2016 6:50 PM
I don't quite get what makes this DigiKey part
suitable for the role of a
fused resistor. I do see that it has specs for 'fusing behavior' but that
aside, I don't see that this series is marketed / sold as a "fusible
resistor".
I take "UL1412 recognised fusing" (sic) on the first line of the data sheet
to mean that they do market them that way.
One reason I question it, is the fact that the fusing
ratings are only
plotted for like 40X or 50X expected current. Can the circuit under
protection be relied upon to produce those levels of current, even under
hard-fault conditions?
I read a little over 1000 seconds to fuse at 10W, which is only a
few times the 2W rating. Admittedly, 20 minutes at 5X load
amounts to a pretty slow fuse. I can only assume their concern
is fire prevention, rather than circuitry protection.
With regard to the suggestion of a fuse and a resistor, you'd
need more room (likely not a problem), and a flameproof
version of the resistor. I don't know anything about UL
ratings, so I don't know if that could be made OK there or
not.
Vince
8:56 p.m.
Vincent & All,
Yes, I read that the series conforms to that particular UL fusing
requirement. My point was that I didn't see any promotion of or expansion
on the fusing qualities of the design. The UL spec almost seemed like an
afterthought. But then, I am not an engineer - so not used to parsing these
documents to such a level.
But you comment on fire prevention is duly noted. As the saying goes, "the
transformer fails open to save the fuse" ;-)
As for a resistor + fuse in series, I suspect you'd want to spec the fuse
for allowable currents - and then spec the resistor to withstand any
current in that range. Point being, you only +need+ one 'weak link' in the
design.
Thoughts?
On Tue, Mar 22, 2016 at 10:20 AM, Vincent Slyngstad <
v.slyngstad at frontier.com> wrote:
From: drlegendre: Monday, March 21, 2016 6:50 PM
I don't quite get what makes this DigiKey
part suitable for the role of a
fused resistor. I do see that it has specs for 'fusing behavior' but that
aside, I don't see that this series is marketed / sold as a "fusible
resistor".
I take "UL1412 recognised fusing" (sic) on the first line of the data sheet
to mean that they do market them that way.
One reason I question it, is the fact that the fusing ratings are only
plotted for like 40X or 50X expected current. Can
the circuit under
protection be relied upon to produce those levels of current, even under
hard-fault conditions?
I read a little over 1000 seconds to fuse at 10W, which is only a few
times the 2W rating. Admittedly, 20 minutes at 5X load amounts to a pretty
slow fuse. I can only assume their concern is fire prevention, rather than
circuitry protection.
With regard to the suggestion of a fuse and a resistor, you'd need more
room (likely not a problem), and a flameproof version of the resistor. I
don't know anything about UL ratings, so I don't know if that could be made
OK there or not.
Vince
21 Mar
21 Mar
8:40 p.m.
On 3/21/16 12:53 PM, Adrian Graham wrote:
On 18/03/2016 02:11, "Josh Dersch"
<derschjo at gmail.com> wrote:
Good news - mine worked so fingers crossed for yours
too. I now have a
functioning PSU again though I've not tried it back in the chassis yet...
Nice! My replacements arrived today and unfortunately I did not have
such good luck. No smoke or fire, but now I get nothing at all out of
the supply. The whine is gone, but there's nothing output at all. The
fuse/resistor didn't blow (it's still got continuity across it) and the
transistor I replaced is still fine, but there must be something else in
the supply that's causing issues...
Blargh. I hate working on power supplies.
- Josh
Onecall
are education-only suppliers but the same part numbers work with
Farnell/Element14. Part# is 1692450.
Thanks! Yes, that looks very similar except mine has a tolerance rating
of 10%. Vincent helpfully pointed me at:
http://www.digikey.com/product-detail/en/tt-electronics-irc/SPP2UL1R00JLF/9…
1272-1-ND/4215463
which look like they should do the job, and I ordered a handful just in
case I ever need a few more. 
22 Mar
22 Mar
12:29 a.m.
Good news - mine worked so fingers crossed for yours
too. I now have a
functioning PSU again though I've not tried it back in the
chassis yet...
Nice! My replacements arrived today and unfortunately I did not have
- Josh
10:53 a.m.
On Tue, Mar 22, 2016 at 12:29 AM, Mattis Lind <mattislind at gmail.com> wrote:
the
Yeah, I have actual original copies of the printsets, too. I have no
excuse, I just get nervous working on these things. I suppose eventually
I'll get used to it.
>> Good
news - mine worked so fingers crossed for yours too. I now have a
> functioning PSU again though I've not tried it back in the chassis
yet...
Nice! My replacements arrived today and unfortunately I did not have
such good
luck. No smoke or fire, but now I get nothing at all out of supply. The whine is gone, but there's
nothing output at all. The
fuse/resistor didn't blow (it's still got continuity across it) and the
transistor I replaced is still fine, but there must be something else in
the supply that's causing issues...
Blargh. I hate working on power supplies.
In this case you have an excellent technical manual and a good schematic
which should help a lot. Working with big SMPSU without schematics or
technical manuals is a not fun.
So here is my piece of advice directly from my head.
1. The PSU has really two AC inputs wired together in the input harness.
You can separate the startup supply part from the SMPSU part. Connect the
startup PSU to a separate AC input and the SMPSU part to a insulation
transformer, a variac and lightbulb in series.
2. Check that the startup PSU, that uses a normal 50/60 Hz transformer
gives the correct voltage. +11 if I remember
correctly.
3. There is a circuit that monitors the input rectified 300VDC voltage and
enables the relay when it has reached a proper voltage. It is a soft start.
Disable it for temporarily. Good idea to check that is working though. If
not the soft start resistors will become overheated when trying to run it
at full load.
The relay (and the circuit driving it) appears to be working -- I hear it
click on at power-up (faintly, over the roar of the fans) and click again
after power-down. I'll hopefully have some time this week to play around
some more, thanks for the suggestions!
I'll note that my earlier statement that I was getting "nothing" out of the
supply turns out to be slightly inaccurate -- with a load, I get nothing
(well, 0.07v) out of the 5V supply; without a load the voltage slowly
increases (maybe 0.5V per second). Didn't let it run long enough to see
where it ends up ;).
Thanks again,
Josh
4. Now you need to have the SMPSU section connected to
AC inlet. On one of
the daughter boards there is a switching bias supply. Check that it
generates the +/-12 V and +5V.
5. Is the main SMPSU switching logic making a nice square wave signal
output. The control board is yet another daughter board.
6. I disconnected the output terminals from the H-bridge to the transformer
and connected a dummy load to be able to have a look at the output
waveform.
7. Reconnect the transformer. The main switch produces +5V and +38V. The
38V is then used on the daughterboards to create all the other voltages,
+/- 12V, +/- 15V, +12V SB, +5VSB (depending on which supply). Is there 38V
here?
8. There is a crowbar circuit on the +5V output terminals. Check that it is
not tripping.
Please note that when working with the +2.5V supply it gets the bias
voltages from the +5V supply. So either get that one working first or
supply bias voltage from a regular PC supply.
/Mattis
- Josh
23 Mar
23 Mar
9:21 p.m.
New subject: DEC H7104-D debugging...
On 3/22/16 12:29 AM, Mattis Lind wrote:
So I had a few minutes tonight to investigate a few things:
- The startup PSU is running, and the relay in the 5V supply is firing
and stays energized until the supply is powered off.
- The +5V, and +/-12V bias voltages are being properly generated. This
makes sense, since the 2.5V supply is working fine. From my
understanding of the supply, this means the 300VDC is also present (also
validated by the relay firing.)
- The 20Khz clock generated on the bias board is present (measured from
pin 8 of J1 on on the bias board), at the proper rate and duty cycle.
- 5V AC and DC LO signals (measured at J1) are .3 and .9V, respectively.
So far, so good. I also measured the 5V Overcurrent and 5V Crowbar on
J1 (pins 2 and 19) and they're at 12V and 8V respectively. I'm not sure
I understand what this indicates; the Overcurrent lamp is not
illuminated on the power controller, for example, and per the tech
manual (section 4.4.2) if an overvoltage occurs and the crowbar kicks
in, the supply should shut down for ~1 second, which I'm not seeing any
indications of (I'm not seeing the voltage reach anything over .2V with
a small load attached). The overcurrent protection appears to work
similarly. I don't see an indication of what the levels for the signals
on J1 are supposed to be, however.
I'll hopefully have more time to debug later this week, thought I'd
report my findings and see if anyone has any bright ideas.
Thanks as always,
- Josh
such good
luck. No smoke or fire, but now I get nothing at all out of the
supply. The whine is gone, but there's nothing output at all. The
fuse/resistor didn't blow (it's still got continuity across it) and the
transistor I replaced is still fine, but there must be something else in
the supply that's causing issues...
Blargh. I hate working on power supplies.
In this case you have an excellent technical manual and a good schematic
which should help a lot. Working with big SMPSU without schematics or
technical manuals is a not fun.
So here is my piece of advice directly from my head.
1. The PSU has really two AC inputs wired together in the input harness.
You can separate the startup supply part from the SMPSU part. Connect the
startup PSU to a separate AC input and the SMPSU part to a insulation
transformer, a variac and lightbulb in series.
2. Check that the startup PSU, that uses a normal 50/60 Hz transformer
gives the correct voltage. +11 if I remember correctly.
3. There is a circuit that monitors the input rectified 300VDC voltage and
enables the relay when it has reached a proper voltage. It is a soft start.
Disable it for temporarily. Good idea to check that is working though. If
not the soft start resistors will become overheated when trying to run it
at full load.
4. Now you need to have the SMPSU section connected to AC inlet. On one of
the daughter boards there is a switching bias supply. Check that it
generates the +/-12 V and +5V.
5. Is the main SMPSU switching logic making a nice square wave signal
output. The control board is yet another daughter board.
6. I disconnected the output terminals from the H-bridge to the transformer
and connected a dummy load to be able to have a look at the output waveform.
7. Reconnect the transformer. The main switch produces +5V and +38V. The
38V is then used on the daughterboards to create all the other voltages,
+/- 12V, +/- 15V, +12V SB, +5VSB (depending on which supply). Is there 38V
here?
8. There is a crowbar circuit on the +5V output terminals. Check that it is
not tripping.
Please note that when working with the +2.5V supply it gets the bias
voltages from the +5V supply. So either get that one working first or
supply bias voltage from a regular PC supply.
/Mattis
24 Mar
24 Mar
3:25 a.m.
New subject: DEC H7104-D debugging...
So I had a few minutes tonight to investigate a few
things:
- The startup PSU is running, and the relay in the 5V supply is firing and
stays energized until the supply is powered off.
- The +5V, and +/-12V bias voltages are being properly generated. This
makes sense, since the 2.5V supply is working fine. From my understanding
of the supply, this means the 300VDC is also present (also validated by the
relay firing.)
- The 20Khz clock generated on the bias board is present (measured from
pin 8 of J1 on on the bias board), at the proper rate and duty cycle.
- 5V AC and DC LO signals (measured at J1) are .3 and .9V, respectively.
Then a lot things seems to be working. Is the main chopper transistor
driven?
First check that you have a signal on the primary side of the pulse
transformer T2 on the mother board? Driven through B22 / B24 from the
control board. Q6 collector.
If not then check backwards towards the NE556, Q6 and Q15. E9 pin 9 and pin
5. E8 pin 3. These outputs are OR:ed together via diodes and drive Q15 base.
If yes then you need to investigate the secondary side of the pulse
transformer T2 on the mother board. (Now it is getting dangerous if you are
not careful). Is there base drive on the power transistors?
So far, so good. I also measured the 5V Overcurrent and 5V Crowbar on J1
(pins 2 and 19) and they're at 12V and 8V respectively. I'm not sure I
understand what this indicates; the Overcurrent lamp is not illuminated on
the power controller, for example, and per the tech manual (section 4.4.2)
if an overvoltage occurs and the crowbar kicks in, the supply should shut
down for ~1 second, which I'm not seeing any indications of (I'm not seeing
the voltage reach anything over .2V with a small load attached). The
overcurrent protection appears to work similarly. I don't see an
indication of what the levels for the signals on J1 are supposed to be,
however.
The NE555 will trigger on a low going TRIG signal, so if either the CROWBAR
SENSE (which is generated by a SCR that sinks this singal to ground when
fired) OR the +5V OVERCURRENT goes low it will trigger. These signals are
active low. I.e you don't have a over current or over voltage condition.
I'll hopefully have more time to debug later this week, thought I'd report
my findings and see if anyone has any bright ideas.
Good luck!
/Mattis
Thanks as always,
- Josh
25 Mar
25 Mar
8:21 p.m.
New subject: DEC H7104-D debugging...
On 3/24/16 3:25 AM, Mattis Lind wrote:
It does seem that way. Thanks for
the suggestions, I have a few (likely
head-scratchingly obvious) questions below. This is not my area of
expertise by a long shot so some of these things are less than obvious
to me. Thanks for being patient :).
So I had a few
minutes tonight to investigate a few things:
- The startup PSU is running, and the relay in the 5V supply is firing and
stays energized until the supply is powered off.
- The +5V, and +/-12V bias voltages are being properly generated. This
makes sense, since the 2.5V supply is working fine. From my understanding
of the supply, this means the 300VDC is also present (also validated by the
relay firing.)
- The 20Khz clock generated on the bias board is present (measured from
pin 8 of J1 on on the bias board), at the proper rate and duty cycle.
- 5V AC and DC LO signals (measured at J1) are .3 and .9V, respectively.
Then a lot things seems to be working. Is the main chopper transistor driven?
How do I
identify which transistor is the main chopper? I've looked
through the schematic and the tech reference and I've come up empty.
First check that you have a signal on the primary side of the pulse
transformer T2 on the mother board? Driven through B22 / B24 from the
control board. Q6 collector.
These are the pins on J4 (on the motherboard) labeled
"-TRIGGER" and
"+TRIGGER" ? Is this safe to probe with a standard 10x oscilloscope
probe (assuming I bring some leads out to where it's safe...)?
If not then check backwards towards the NE556, Q6 and Q15. E9 pin 9 and pin
5. E8 pin 3. These outputs are OR:ed together via diodes and drive Q15 base.
Makes sense.
If yes then you need to investigate the secondary side of the pulse
transformer T2 on the mother board. (Now it is getting dangerous if you are
not careful). Is there base drive on the power transistors?
What precautions do you
recommend taking here?
Thanks again. I may have some time this weekend to play with this, but
I have family coming to visit, so probably not :). I'll let you know
how I get on if I do, though...
- Josh
So far, so good. I also measured the 5V
Overcurrent and 5V Crowbar on J1
(pins 2 and 19) and they're at 12V and 8V respectively. I'm not sure I
understand what this indicates; the Overcurrent lamp is not illuminated on
the power controller, for example, and per the tech manual (section 4.4.2)
if an overvoltage occurs and the crowbar kicks in, the supply should shut
down for ~1 second, which I'm not seeing any indications of (I'm not seeing
the voltage reach anything over .2V with a small load attached). The
overcurrent protection appears to work similarly. I don't see an
indication of what the levels for the signals on J1 are supposed to be,
however.
The NE555 will trigger on a low going TRIG signal, so if either the CROWBAR
SENSE (which is generated by a SCR that sinks this singal to ground when
fired) OR the +5V OVERCURRENT goes low it will trigger. These signals are
active low. I.e you don't have a over current or over voltage condition.
I'll hopefully have more time to debug later
this week, thought I'd report
my findings and see if anyone has any bright ideas.
Good luck!
/Mattis
> Thanks as always,
> - Josh
>
>
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cclist＠sydex.com -
derschjo＠gmail.com -
dkelvey＠hotmail.com -
drlegendre＠gmail.com -
mattislind＠gmail.com -
v.slyngstad＠frontier.com -
witchy＠binarydinosaurs.co.uk