RE: H7874 power supply
> Jon Elson wrote: >The VAX 11/780 absolutely had power fail, and it DID work. So did the 11/730 and I imagine the 750 as well. No core, but there was a battery backup option to keep main memory alive and refreshed even in the event of power failure. >I did this quite often while swapping I/O devices and such >after device drivers became loadable. It was (is!) quite handy on the 730 as well. If your configuration has a separate BA11-K for the UNIBUS peripherals, then you can power down that box without turning off the CPU. It took 20-25 minutes to boot up the 730 from a dead start, so this was a great time saver. Bob
Re: H7874 power supply
On 03/30/2020 11:49 AM, Paul Koning via cctalk wrote: Thise signals don't seem like a problem: just hardwire them to the desired logic level. PDP-11s need a real functioning DCOK signal iff you want to do power fail interrupt handling, otherwise they don't. Do VAXen have power fail interrupt? If yes, does anyone actually use it? The VAX 11/780 absolutely had power fail, and it DID work. You could just walk up to the CPU and turn the key to standby, and it would power down everything but the memory. When you turned the key back to on, it would power up, load microcode and resume the paused system image VERY smoothly. You could also power down the Unibus box, and it would recover all the devices and resume when you turned it back on. Anything tasks that ran off Massbus peripherals could keep running while the Unibus was off. I did this quite often while swapping I/O devices and such after device drivers became loadable. Jon
Re: H7874 power supply
Vectoring through 24 was very important back in the core memory days when the memory would still be there after a power failure and you wnated the system to keep running, as was our Ontario Bellboy paging controller. cheers, Nigel On 30/03/2020 12:49, Paul Koning via cctalk wrote: On Mar 30, 2020, at 10:17 AM, Robert Armstrong via cctalk wrote: Looks like for this enclosure an ATX supply could well work. For my VAX my notes say it didn't. A VAX would certainly be harder. You'd have to kludge up the ACOK and DCOK signals for one thing, which I don't think the R400x uses. Thise signals don't seem like a problem: just hardwire them to the desired logic level. PDP-11s need a real functioning DCOK signal iff you want to do power fail interrupt handling, otherwise they don't. Do VAXen have power fail interrupt? If yes, does anyone actually use it? paul -- Nigel Johnson MSc., MIEEE VE3ID/G4AJQ/VA3MCU Amateur Radio, the origin of the open-source concept! You can reach me by voice on Skype: TILBURY2591 If time travel ever will be possible, it already is. Ask me again yesterday This e-mail is not and cannot, by its nature, be confidential. En route from me to you, it will pass across the public Internet, easily readable by any number of system administrators along the way. Nigel Johnson Please consider the environment when deciding if you really need to print this message
Re: H7874 power supply
> On Mar 30, 2020, at 10:17 AM, Robert Armstrong via cctalk > wrote: > >> Looks like for this enclosure an ATX supply could well work. >> For my VAX my notes say it didn't. > > A VAX would certainly be harder. You'd have to kludge up the ACOK and DCOK > signals for one thing, which I don't think the R400x uses. Thise signals don't seem like a problem: just hardwire them to the desired logic level. PDP-11s need a real functioning DCOK signal iff you want to do power fail interrupt handling, otherwise they don't. Do VAXen have power fail interrupt? If yes, does anyone actually use it? paul
RE: H7874 power supply
>Looks like for this enclosure an ATX supply could well work. > For my VAX my notes say it didn't. A VAX would certainly be harder. You'd have to kludge up the ACOK and DCOK signals for one thing, which I don't think the R400x uses. It'd be really handy to find even a schematic for the backplane so we could see which signals are actually connected, but I did some searching and came up with nothing. Oh, and I did try to power up the H7874 on the bench for testing, but it wouldn't turn on there either. It probably has a minimum load requirement, or it needs some signal from the backplane to turn on. FWIW, the R400x does not have a power switch - the only way to turn it on or off is thru the H7874, either by the circuit breaker or the power control bus. The R400x also has several large power resistors on the M7493 SCSI connector module; those may be there to provide a minimum load for the power supply. Bob
RE: H7874 power supply
> -Original Message- > From: cctech On Behalf Of Robert > Armstrong via cctech > Sent: 29 March 2020 23:15 > To: r...@jarratt.me.uk; 'General Discussion: On-Topic Posts' > ; 'Maciej W. Rozycki' > Subject: RE: H7874 power supply > > Remembering that I have the R400x enclosure and I'm only interested in > powering disk drives - I looked up the specs for the RF7x drives, and they > all use > about 1.5A at 5V and 2.5-3A operating at 12V. There's a 5-6A spinup surge on > the 12V supply, but as long as you spin them up in sequence you can probably > gloss over that. Anyway, I have 4xRF7x drives and two SCSI drives, so figure > maybe 20A at 12V and 10A at 5V. That's entirely doable with an ATX supply. > > The fans, annoyingly, are 24VDC so those would either have to be replaced > with 12V fans or I'd have to kludge up an extra 24V supply. > > My next step was to figure out the pinout of the connectors on the back of > the > H7874. The big, high current, pins aren't marked anywhere inside the H7874 > that I could find but, conveniently, they ARE marked on the R400x backplane. > There are also a couple of high density connectors sandwiched in between the > power pins; the lower one doesn't appear to be used but the upper one has a > few connections. From looking at the backplane it appears that only four pins > in the upper connector are actually connected. That's a guess though, because > I can't see that back side of the backplane. > > I needed to see more of the backplane to figure out where these four > connections went, so I removed all the drives from the R400x. Then, on a > whim, I stuck the H7874 back in there and tried to power it up. It works! It > appears that I don't have a bad power supply after all; I have a bad drive > somewhere. Don't I feel silly :) > I would just say that you must be hugely relieved! Looks like for this enclosure an ATX supply could well work. For my VAX my notes say it didn't. It would still be worth checking the ESR on the electrolytic capacitors and replacing any suspect ones while you are at it. > So I don't need to fool with the ATX supply after all, or at least not > until my PS > really does die. Thanks for the help, and sorry for the false alarm. > > Bob > > > -Original Message- > From: Rob Jarratt [mailto:robert.jarr...@ntlworld.com] > Sent: Sunday, March 29, 2020 2:05 PM > To: b...@jfcl.com; 'General Discussion: On-Topic Posts'; 'Maciej W. Rozycki' > Cc: r...@jarratt.me.uk > Subject: RE: H7874 power supply > > I have some notes I made about trying a PC PSU, I don't think it really > worked, > there are signals to indicate power OK and perhaps others. But perhaps a more > concerted effort might yield something that could work. > > Regards > > Rob > > > -Original Message- > > From: cctech On Behalf Of Robert > > Armstrong via cctech > > Sent: 29 March 2020 19:15 > > To: 'Maciej W. Rozycki' ; 'General Discussion: > > On- Topic Posts' > > Cc: r...@jarratt.me.uk > > Subject: RE: H7874 power supply > > > > >Maciej W. Rozycki wrote: > > >numerous Chemi-Con SXF parts scattered across all boards, some > > >leaking > > > > Yeah, mine is full of "Nippon Chemi-Con" electrolytic too. > > > > What about just gutting the PS chassis and sticking in an ATX power > > supply? I don't know how the maximum current per output breaks down, > > but as I understand it the H7874 is only a 600W supply. That's not a > > problem for an ATX supply, and it would have all the required output > > voltages. You'd have to run the cabinet fans at a fixed speed and > > you'd lose the power control bus feature, but that's not a show stopper. > > > > Actually my unit is in an R400x chassis full of RF drives, so I > > believe I only need > > +12 and +5. I don't think the 3.3v and -12 are used in that case. I > > +wonder how > > much current I really need for the drives? I should look that up and > > I might be able to find a surplus dual output supply that would do the job. > > > > Thanks again, > > Bob
RE: H7874 power supply
Remembering that I have the R400x enclosure and I'm only interested in powering disk drives - I looked up the specs for the RF7x drives, and they all use about 1.5A at 5V and 2.5-3A operating at 12V. There's a 5-6A spinup surge on the 12V supply, but as long as you spin them up in sequence you can probably gloss over that. Anyway, I have 4xRF7x drives and two SCSI drives, so figure maybe 20A at 12V and 10A at 5V. That's entirely doable with an ATX supply. The fans, annoyingly, are 24VDC so those would either have to be replaced with 12V fans or I'd have to kludge up an extra 24V supply. My next step was to figure out the pinout of the connectors on the back of the H7874. The big, high current, pins aren't marked anywhere inside the H7874 that I could find but, conveniently, they ARE marked on the R400x backplane. There are also a couple of high density connectors sandwiched in between the power pins; the lower one doesn't appear to be used but the upper one has a few connections. From looking at the backplane it appears that only four pins in the upper connector are actually connected. That's a guess though, because I can't see that back side of the backplane. I needed to see more of the backplane to figure out where these four connections went, so I removed all the drives from the R400x. Then, on a whim, I stuck the H7874 back in there and tried to power it up. It works! It appears that I don't have a bad power supply after all; I have a bad drive somewhere. Don't I feel silly :) So I don't need to fool with the ATX supply after all, or at least not until my PS really does die. Thanks for the help, and sorry for the false alarm. Bob -Original Message- From: Rob Jarratt [mailto:robert.jarr...@ntlworld.com] Sent: Sunday, March 29, 2020 2:05 PM To: b...@jfcl.com; 'General Discussion: On-Topic Posts'; 'Maciej W. Rozycki' Cc: r...@jarratt.me.uk Subject: RE: H7874 power supply I have some notes I made about trying a PC PSU, I don't think it really worked, there are signals to indicate power OK and perhaps others. But perhaps a more concerted effort might yield something that could work. Regards Rob > -Original Message- > From: cctech On Behalf Of Robert > Armstrong via cctech > Sent: 29 March 2020 19:15 > To: 'Maciej W. Rozycki' ; 'General Discussion: On- > Topic Posts' > Cc: r...@jarratt.me.uk > Subject: RE: H7874 power supply > > >Maciej W. Rozycki wrote: > >numerous Chemi-Con SXF parts scattered across all boards, some leaking > > Yeah, mine is full of "Nippon Chemi-Con" electrolytic too. > > What about just gutting the PS chassis and sticking in an ATX power supply? > I > don't know how the maximum current per output breaks down, but as I > understand it the H7874 is only a 600W supply. That's not a problem for an > ATX supply, and it would have all the required output voltages. You'd have to > run the cabinet fans at a fixed speed and you'd lose the power control bus > feature, but that's not a show stopper. > > Actually my unit is in an R400x chassis full of RF drives, so I believe I > only need > +12 and +5. I don't think the 3.3v and -12 are used in that case. I wonder > how > much current I really need for the drives? I should look that up and I might > be > able to find a surplus dual output supply that would do the job. > > Thanks again, > Bob
RE: H7874 power supply
I have some notes I made about trying a PC PSU, I don't think it really worked, there are signals to indicate power OK and perhaps others. But perhaps a more concerted effort might yield something that could work. Regards Rob > -Original Message- > From: cctech On Behalf Of Robert > Armstrong via cctech > Sent: 29 March 2020 19:15 > To: 'Maciej W. Rozycki' ; 'General Discussion: On- > Topic Posts' > Cc: r...@jarratt.me.uk > Subject: RE: H7874 power supply > > >Maciej W. Rozycki wrote: > >numerous Chemi-Con SXF parts scattered across all boards, some leaking > > Yeah, mine is full of "Nippon Chemi-Con" electrolytic too. > > What about just gutting the PS chassis and sticking in an ATX power supply? > I > don't know how the maximum current per output breaks down, but as I > understand it the H7874 is only a 600W supply. That's not a problem for an > ATX supply, and it would have all the required output voltages. You'd have to > run the cabinet fans at a fixed speed and you'd lose the power control bus > feature, but that's not a show stopper. > > Actually my unit is in an R400x chassis full of RF drives, so I believe I > only need > +12 and +5. I don't think the 3.3v and -12 are used in that case. I wonder > how > much current I really need for the drives? I should look that up and I might > be > able to find a surplus dual output supply that would do the job. > > Thanks again, > Bob
RE: H7874 power supply
I forgot to mention that I replaced a fair number of capacitors, even ones that had not leaked, because their ESR was a bit suspect. I have some notes, but it is hard to reconstruct exactly what I did. Regards Rob > -Original Message- > From: cctech On Behalf Of Maciej W. > Rozycki via cctech > Sent: 29 March 2020 17:18 > To: b...@jfcl.com; General Discussion: On-Topic Posts > > Cc: r...@jarratt.me.uk > Subject: RE: H7874 power supply > > On Sun, 29 Mar 2020, Robert Armstrong via cctech wrote: > > > And then there's a giant PCB, almost 11" square, covered with > > opamps, 74LS logic and discrete parts. There are filter caps, a > > transformer, and switching transistors on this board too so it > > obviously produces yet another power output for something. Oh, and I > > think this cabinet has variable speed fans, right? SO there's probably a > > fan > speed controller on here as well. > > There's logic included there for synchronised control of multiple H7874 PSUs > at > once in a master-slave configuration via a set of auxiliary connectors so as > to > power up or down all pieces simultaneously in a complex machine setup with > storage and/or Q-bus expansion boxes. No documentation for the PSU has > been chased so far as far as I know. > > Note that also with this PSU there were capacitors used that suffered from > the > issue with the quaternary ammonium salt system used in the electrolyte. All > mine had numerous Chemi-Con SXF parts scattered across all boards, some > leaking. They are prone to leaks even if unused and have to be replaced. > Especially those next to the 5V circuit are hard to get to to desolder and > replace. Also Chemi-Con SXE parts present in this PSU are reportedly affected > although I haven't seen them leak myself. > > This PSU has been my worst nightmare as far as keeping old equipment alive > has been concerned. I was able to make just one working PSU out of three > broken ones by mixing and matching individual pieces with caps replaced until > I > found one set that worked. I consider replacing the large cuboid 6800µF > Sprague part as well as I have seen its capacitance drop down to like half of > its > nominal. > > Maciej
RE: H7874 power supply
>Maciej W. Rozycki wrote: >numerous Chemi-Con SXF parts scattered across >all boards, some leaking Yeah, mine is full of "Nippon Chemi-Con" electrolytic too. What about just gutting the PS chassis and sticking in an ATX power supply? I don't know how the maximum current per output breaks down, but as I understand it the H7874 is only a 600W supply. That's not a problem for an ATX supply, and it would have all the required output voltages. You'd have to run the cabinet fans at a fixed speed and you'd lose the power control bus feature, but that's not a show stopper. Actually my unit is in an R400x chassis full of RF drives, so I believe I only need +12 and +5. I don't think the 3.3v and -12 are used in that case. I wonder how much current I really need for the drives? I should look that up and I might be able to find a surplus dual output supply that would do the job. Thanks again, Bob
Re: H7874 power supply
> On Mar 29, 2020, at 2:14 PM, Robert Armstrong via cctech > wrote: > >> Maciej W. Rozycki wrote: >> numerous Chemi-Con SXF parts scattered across >> all boards, some leaking > > Yeah, mine is full of "Nippon Chemi-Con" electrolytic too. > > What about just gutting the PS chassis and sticking in an ATX power supply? > I don't know how the maximum current per output breaks down, but as I > understand it the H7874 is only a 600W supply. That's not a problem for an > ATX supply, and it would have all the required output voltages. You'd have > to run the cabinet fans at a fixed speed and you'd lose the power control bus > feature, but that's not a show stopper. > > Actually my unit is in an R400x chassis full of RF drives, so I believe I > only need +12 and +5. I don't think the 3.3v and -12 are used in that case. > I wonder how much current I really need for the drives? I should look that > up and I might be able to find a surplus dual output supply that would do the > job. I had a similar thought for a PRO supply that blew its input filter (of all things). It does +5, +12, and -12. The -12 is needed at least for RS232. paul
RE: H7874 power supply
On Sun, 29 Mar 2020, Robert Armstrong via cctech wrote: > And then there's a giant PCB, almost 11" square, covered with opamps, 74LS > logic and discrete parts. There are filter caps, a transformer, and > switching transistors on this board too so it obviously produces yet another > power output for something. Oh, and I think this cabinet has variable speed > fans, right? SO there's probably a fan speed controller on here as well. There's logic included there for synchronised control of multiple H7874 PSUs at once in a master-slave configuration via a set of auxiliary connectors so as to power up or down all pieces simultaneously in a complex machine setup with storage and/or Q-bus expansion boxes. No documentation for the PSU has been chased so far as far as I know. Note that also with this PSU there were capacitors used that suffered from the issue with the quaternary ammonium salt system used in the electrolyte. All mine had numerous Chemi-Con SXF parts scattered across all boards, some leaking. They are prone to leaks even if unused and have to be replaced. Especially those next to the 5V circuit are hard to get to to desolder and replace. Also Chemi-Con SXE parts present in this PSU are reportedly affected although I haven't seen them leak myself. This PSU has been my worst nightmare as far as keeping old equipment alive has been concerned. I was able to make just one working PSU out of three broken ones by mixing and matching individual pieces with caps replaced until I found one set that worked. I consider replacing the large cuboid 6800µF Sprague part as well as I have seen its capacitance drop down to like half of its nominal. Maciej
RE: H7874 power supply
> Rob Jarratt >robert.jarr...@ntlworld.com> wrote: > I reverse engineered the schematic of the 12V output board. I >don't know if that would be of any use? How correct it is I don't know. Sure, if you don't mind sharing. Everything helps. Looks like there are five separate PCBs in there. There's one long, skinny one that's obviously the AC input and rectifier board, which probably produces something like 300VDC for the regulator boards. There are two similar but not identical boards with huge heat sinks that are obviously the output regulators. I think this PS has +5, +3.3, +12 and -12 volt outputs, but I've no idea which board does which. And then there's a giant PCB, almost 11" square, covered with opamps, 74LS logic and discrete parts. There are filter caps, a transformer, and switching transistors on this board too so it obviously produces yet another power output for something. Oh, and I think this cabinet has variable speed fans, right? SO there's probably a fan speed controller on here as well. You'd think that will all this logic it could at least have some LEDs or something to tell me which output has failed, but it doesn't seem like it. Thanks Bob
RE: H7874 power supply
OK, I posted it here: https://robs-old-computers.com/2020/03/29/h7874-power-supply/ > -Original Message- > From: Robert Armstrong > Sent: 29 March 2020 15:44 > To: r...@jarratt.me.uk; 'General Discussion: On-Topic Posts' > > Subject: RE: H7874 power supply > > > Rob Jarratt >robert.jarr...@ntlworld.com> wrote: > > I reverse engineered the schematic of the 12V output board. I don't > >know if that would be of any use? How correct it is I don't know. > > Sure, if you don't mind sharing. Everything helps. > > Looks like there are five separate PCBs in there. There's one long, skinny one > that's obviously the AC input and rectifier board, which probably produces > something like 300VDC for the regulator boards. There are two similar but not > identical boards with huge heat sinks that are obviously the output regulators. I > think this PS has +5, +3.3, +12 and -12 volt outputs, but I've no idea which board > does which. > > And then there's a giant PCB, almost 11" square, covered with opamps, 74LS > logic and discrete parts. There are filter caps, a transformer, and switching > transistors on this board too so it obviously produces yet another power output > for something. Oh, and I think this cabinet has variable speed fans, right? SO > there's probably a fan speed controller on here as well. > > You'd think that will all this logic it could at least have some LEDs or > something to tell me which output has failed, but it doesn't seem like it. > > Thanks > Bob
Re: H7874 power supply
Rob Jarratt via cctech wrote: > > > > -Original Message- > > From: cctech On Behalf Of Robert > > Armstrong via cctech > > Sent: 29 March 2020 02:29 > > To: cct...@classiccmp.org > > Subject: H7874 power supply > > > > Does anybody have a maintenance print or service manual for the DEC > > H7874? > > This is the power supply used in the BA4xx and R400x cabinets. As you > might > > guess, I have one that tries to power up but shuts down after a second. > > Probably a bad capacitor (or several), but this thing is ridiculously > complicated > > and not all that easy to disassemble, either. I'd like to be able to > trouble shoot > > it rather than just firing the proverbial parts cannon at it. FWIW, none > of the > > electrolytic (of which there are many) have obviously failed - no leaking, > no > > bulges, etc. Of course, that proves fairly little. > > > > This PSU is a real problem, as you say, complicated and hard to disassemble. > I had one that didn't work, if I remember correctly in the end I had to get > another one. I have a second machine with this PSU which has an intermittent > problem and shuts itself down after a few minutes if it hasn't been used for > a while, but a subsequent power up sees it work for as long as I need it. > > It looks like I reverse engineered the schematic of the 12V output board. I > don't know if that would be of any use? How correct it is I don't know. > > Regards > > Rob > > I would be interested. I have an VAX400/300 with such an working again PSU, Changed Capacitors two years before..now it works. A friend gave me another PSU with a similar fault, changed capacitors as before on the other one..but no luck at all. It still powers down shortly after switching on. Yes..thats the most ugly PSU Design I ever saw..and I'm interested in schematics or parts of them.. Regards, Holm -- Technik Service u. Handel Tiffe, www.tsht.de, Holm Tiffe, Freiberger Straße 42, 09600 Oberschöna, USt-Id: DE253710583 i...@tsht.de Fax +49 3731 74200 Tel +49 3731 74222 Mobil: 0172 8790 741
RE: H7874 power supply
> -Original Message- > From: cctech On Behalf Of Robert > Armstrong via cctech > Sent: 29 March 2020 02:29 > To: cct...@classiccmp.org > Subject: H7874 power supply > > Does anybody have a maintenance print or service manual for the DEC > H7874? > This is the power supply used in the BA4xx and R400x cabinets. As you might > guess, I have one that tries to power up but shuts down after a second. > Probably a bad capacitor (or several), but this thing is ridiculously complicated > and not all that easy to disassemble, either. I'd like to be able to trouble shoot > it rather than just firing the proverbial parts cannon at it. FWIW, none of the > electrolytic (of which there are many) have obviously failed - no leaking, no > bulges, etc. Of course, that proves fairly little. > This PSU is a real problem, as you say, complicated and hard to disassemble. I had one that didn't work, if I remember correctly in the end I had to get another one. I have a second machine with this PSU which has an intermittent problem and shuts itself down after a few minutes if it hasn't been used for a while, but a subsequent power up sees it work for as long as I need it. It looks like I reverse engineered the schematic of the 12V output board. I don't know if that would be of any use? How correct it is I don't know. Regards Rob > > > Thanks, > > Bob Armstrong > >
H7874 power supply
Does anybody have a maintenance print or service manual for the DEC H7874? This is the power supply used in the BA4xx and R400x cabinets. As you might guess, I have one that tries to power up but shuts down after a second. Probably a bad capacitor (or several), but this thing is ridiculously complicated and not all that easy to disassemble, either. I'd like to be able to trouble shoot it rather than just firing the proverbial parts cannon at it. FWIW, none of the electrolytic (of which there are many) have obviously failed - no leaking, no bulges, etc. Of course, that proves fairly little. Thanks, Bob Armstrong
