On Thu, 12 May 2022, Peter Coghlan via cctalk wrote:
> > Wayne: I just got an Dec AlphaStation 200. Look like its running NT
> > though.
> >
>
> It's probably ok but check the power supply for leaky capacitors!
Definitely, watch out for possible damage!
Prompted I had a peek in mine (an As
> On May 13, 2022, at 3:36 AM, Christian Corti via cctalk
> wrote:
>
> On Thu, 12 May 2022, Peter Coghlan wrote:
> ...
>> A variac does not provide isolation. If it is not wired correctly, it is
>
> Good "variacs" provide galvanic isolation from the mains, i.e. they are not
> autotransform
On Thu, 12 May 2022, Peter Coghlan wrote:
Can we agree that there is such a thing as an "AC current" and there
is such a thing as a "DC current" and the two of them can be added
together?
Ouch... an alternating current current and direct current current ;-)
And you usually add the voltages, not
On Thu, 12 May 2022, Toby Thain wrote:
It does not, due to unidirectionality.
But in general, diodes can be (and are) used as controlled AC switches.
One good example are the head select diodes in disk drives. You apply a
direct voltage and thus "open" the diode. You then have a overlayed
al
On Thu, 12 May 2022, Toby Thain wrote:
I also hate the English/American expression "inverter" for voltage
converters, because really nothing is being inverted in any way.
Generating AC from DC _does_ always involve generation of "inverted" voltages
relative to the input DC (AC has positive and n
>>
>> If I am trying to calculate the height a sea harbour wall needs to be, can I
>> not consider the height of the tide and the height of the waves separately
>> and add them together, just to make it easier to work it out even though I
>> know that it would be physically impossible to disti
> On 05/12/2022 2:14 PM Peter Coghlan via cctalk wrote:
>
>
> Wayne S wrote:
> >> On May 12, 2022, at 09:56, Peter Coghlan via cctalk
> >> wrote:
> >>
> >> Toby Thain via cctalk wrote:
> On 2022-05-11 7:02 p.m., Peter Coghlan via cctalk wrote:
> Given the normal usage that has evo
Wayne S wrote:
>> On May 12, 2022, at 09:56, Peter Coghlan via cctalk
>> wrote:
>>
>> Toby Thain via cctalk wrote:
On 2022-05-11 7:02 p.m., Peter Coghlan via cctalk wrote:
Given the normal usage that has evolved for the terms DC and AC rather than
their dictionary definitions
On 2022-05-12 11:37 a.m., Peter Coghlan via cctalk wrote:
Toby Thain via cctalk wrote:
On 2022-05-11 7:02 p.m., Peter Coghlan via cctalk wrote:
Given the normal usage that has evolved for the terms DC and AC
rather than
their dictionary definitions, I would suggest that the current that gets
> On May 12, 2022, at 11:37 AM, Peter Coghlan via cctalk
> wrote:
>
> Toby Thain via cctalk wrote:
>> On 2022-05-11 7:02 p.m., Peter Coghlan via cctalk wrote:
>>> Given the normal usage that has evolved for the terms DC and AC rather than
>>> their dictionary definitions, I would suggest that
Toby Thain via cctalk wrote:
On 2022-05-11 7:02 p.m., Peter Coghlan via cctalk wrote:
Given the normal usage that has evolved for the terms DC and AC rather than
their dictionary definitions, I would suggest that the current that gets
passed by a rectifier has both a DC component and an AC comp
On Thu, 12 May 2022, Peter Coghlan via cctalk wrote:
> I replaced the capacitor in question with a blue Nichicon SE of the same
> value scavanged from another H7821 until I order some spares. I now have
> 8.7V available on the 9V supply, a little less than I hoped for but it is
> enough to make t
On Wed, 11 May 2022, Paul Koning wrote:
> > I guess especially for standard capacitors factories ordered whatever was
> > readily available whereas with the high-ripple low-impedance/ESR parts the
> > choice was much more limited.
>
> I wonder if nowadays a good replacement for the case where l
On 2022-05-12 4:40 a.m., Christian Corti via cctalk wrote:
On Thu, 12 May 2022, Peter Coghlan wrote:
about it? Maybe it would be more accurate to use terms like steady
voltage
and alternating voltage? Alternating doesn't seem like that good a term
In German it's exactly like you suggest it.
On 2022-05-11 7:02 p.m., Peter Coghlan via cctalk wrote:
It's hard to come up with suitable terms for this sort of stuff that
convey the meaning of what is going on. I struggled with it for a while
and that was what I ended up with.
With the strict meaning of DC and AC being direct current and
>
> Wayne: AC DC terminology has been well documented since the 1800's.
> Don't try to reinvent the terms or no one will know what you are talking
> about.
> I answered a few things below...
>
They didn't have switch mode power supplies in the 1800s. Terms like AC and
DC as understood back th
Maciej W. Rozycki wrote:
> On Thu, 12 May 2022, Peter Coghlan via cctalk wrote:
>
>> Anyway, the good news is that I think I have found the source of the
>> problem. One of the capacitors used to filter the (DC?, pulsed DC?,
>> rippled DC?, biased AC?) supply to the 9V regulator is marked 330uF/
On Thu, 12 May 2022, Peter Coghlan wrote:
about it? Maybe it would be more accurate to use terms like steady voltage
and alternating voltage? Alternating doesn't seem like that good a term
In German it's exactly like you suggest it. We say "Gleichspannung" (=
constant/steady voltage) and "Wec
> On May 11, 2022, at 9:00 PM, Maciej W. Rozycki via cctalk
> wrote:
>
> ...
> I guess especially for standard capacitors factories ordered whatever was
> readily available whereas with the high-ripple low-impedance/ESR parts the
> choice was much more limited.
I wonder if nowadays a good
On Thu, 12 May 2022, Peter Coghlan via cctalk wrote:
> Anyway, the good news is that I think I have found the source of the
> problem. One of the capacitors used to filter the (DC?, pulsed DC?,
> rippled DC?, biased AC?) supply to the 9V regulator is marked 330uF/25V.
> It reads 6uF on the capaci
It's hard to come up with suitable terms for this sort of stuff that
convey the meaning of what is going on. I struggled with it for a while
and that was what I ended up with.
With the strict meaning of DC and AC being direct current and alternating
current and given that we are often talking abo
Christian Corti via cctalk wrote:
On Tue, 10 May 2022, Peter Coghlan wrote:
> Ahead of the 78M09 is another TO220 package marked D45H8 which seems to
> be a transistor. Then I am completely lost. I can't find the rectifier
That TO220 part would be the rectifier. It either has two legs (simple
On Tue, 10 May 2022, Peter Coghlan wrote:
Ahead of the 78M09 is another TO220 package marked D45H8 which seems to
be a transistor. Then I am completely lost. I can't find the rectifier
That TO220 part would be the rectifier. It either has two legs (simple
diode) or three (two-wave rectifier
Peter Coghlan wrote:
> Tony Duell wrote:
> > On Sun, May 8, 2022 at 1:02 PM Maciej W. Rozycki via cctalk
> > wrote:
> >
> > > In the H7821 it's -9Vdc return pairing with -9Vdc supplied on the yellow
> > > wire (an isolated circuit). Pin numbers 14 & 13. Try measuring voltage
> > > across the su
On Mon, May 9, 2022 at 2:27 PM Paul Koning via cctalk
wrote:
>
> Why would you expect a transceiver power supply to be isolated from system
> ground? The transceiver logic ground (via the AUI connector) is tied to the
> system ground. It is the coax that is isolated from the system ground, not
> On May 8, 2022, at 7:04 PM, Maciej W. Rozycki via cctalk
> wrote:
>
> On Sun, 8 May 2022, Tony Duell wrote:
>
>>> In the H7821 it's -9Vdc return pairing with -9Vdc supplied on the yellow
>>> wire (an isolated circuit). Pin numbers 14 & 13. Try measuring voltage
>>> across the suspicious
Tony Duell wrote:
> On Sun, May 8, 2022 at 1:02 PM Maciej W. Rozycki via cctalk
> wrote:
>
> > In the H7821 it's -9Vdc return pairing with -9Vdc supplied on the yellow
> > wire (an isolated circuit). Pin numbers 14 & 13. Try measuring voltage
> > across the suspicious connections as any referen
Hi Maciej,
>
> >
> > What is H7826 used in? I don't think I have any of those.
>
> DECstation 5000/1xx systems and TURBOchannel Extender boxes. Not sure if
> anything else.
>
Ok. I have VAXStation/MicroVAX and Alpha systems but no DECStations so that
explains why I haven't seen them.
>
> >
On Sun, 8 May 2022, Tony Duell wrote:
> > In the H7821 it's -9Vdc return pairing with -9Vdc supplied on the yellow
> > wire (an isolated circuit). Pin numbers 14 & 13. Try measuring voltage
> > across the suspicious connections as any reference to ground may not be
> > indicative.
> >
> > This
On Sun, May 8, 2022 at 1:02 PM Maciej W. Rozycki via cctalk
wrote:
> In the H7821 it's -9Vdc return pairing with -9Vdc supplied on the yellow
> wire (an isolated circuit). Pin numbers 14 & 13. Try measuring voltage
> across the suspicious connections as any reference to ground may not be
> ind
Hi Peter,
> > Right, my notes indicate Nichicon PL parts might be problematic too, e.g.
> > one at 4700uF/10V on 5V output of the H7826 PSU.
> >
>
> What is H7826 used in? I don't think I have any of those.
DECstation 5000/1xx systems and TURBOchannel Extender boxes. Not sure if
anything el
Hi Maciej,
>
> Right, my notes indicate Nichicon PL parts might be problematic too, e.g.
> one at 4700uF/10V on 5V output of the H7826 PSU.
>
What is H7826 used in? I don't think I have any of those.
>
> I can confirm now Nichicon PF 47uF/35V parts to be the source of an issue
> with my Bel P
Hi Peter,
> I still have the leaky electrolytics I removed from the POWER-ONE PSU in my
> Cisco IGS a while back. I stored them with their leads up and goo seems to
> be still oozing out of some of them despite their inactivity and orientation.
> These ones are marked Nichicon PL(M) 4700uF/63V, 2
Hi Maciej,
Thanks for your input.
"Maciej W. Rozycki" wrote:
>
> Lying on a side would also permit leaking, I've seen an H7821 damaged in
> storage that way. Gravity only helps with the leads up.
>
I have lots of H7821s that were on their side for a few years and leaked a
lot but I also have H
On Tue, 3 May 2022, Peter Coghlan via cctalk wrote:
> > Would the system have been possibly stored upside down sometime?
> >
>
> I don't think so. It may have spent some time lying on it's side due to
> deteriorating rubber feet and for ease of access and but I can't see any
> reason for it ever
"Maciej W. Rozycki" wrote:
>On Mon, 2 May 2022, Peter Coghlan via cctalk wrote:
>
>> Thankfully, it doesn't seem to have been there long and didn't get a chance
>> to spread around the board. Bizarrely this capacitor has it's legs pointing
>> upwards and managed to leak while there are similar cap
"Maciej W. Rozycki" wrote:
>On Mon, 2 May 2022, Peter Coghlan via cctalk wrote:
>
>> Thankfully, it doesn't seem to have been there long and didn't get a chance
>> to spread around the board. Bizarrely this capacitor has it's legs pointing
>> upwards and managed to leak while there are similar cap
On Mon, 2 May 2022, Peter Coghlan via cctalk wrote:
> Thankfully, it doesn't seem to have been there long and didn't get a chance
> to spread around the board. Bizarrely this capacitor has it's legs pointing
> upwards and managed to leak while there are similar capacitors on the other
> board wit
I wrote:
>
> At least the H7822 does not seem to suffer from the leaky capacitor problem
> like the H7821 does.
>
Well, it's made a liar of me already. While checking over my previous work
replacing the zener diode to make sure I didn't break something else, my
eye was drawn to a ring of sticky b
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