I used a Vishay GBPC3506W-E4/51, which is 600V 35A, 400A inrush rated. Looks like they're currently on-order at Mouser, I don't know about other suppliers.
The GBPC3506W-E4/51 is a little thinner than the bridge rectifier DEC used originally, which sometimes matters. For the 5411086 board in my PDP-11/10, height does matter, as it shares a heatsink with other parts. I stacked a few washers under the center of the bridge: http://www.glitchwrks.com/images/dec/pdp1110_psu_repair/rectifier_spacer.jpg Thanks, Jonathan ------- Original Message ------- On Thursday, February 17th, 2022 at 17:57, Rob Jarratt via cctalk <cctalk@classiccmp.org> wrote: > Hmmm this would suggest 200V 20A > > https://archive.org/stream/bitsavers_decfieldSeeTechnicalManual1972_19126909 > > 8/DEC_Field_Service_Technical_Manual_1972_djvu.txt rather than 35A. Given > > the 20-30VAC input though, I presume a 50V part would be OK still? > > > -----Original Message----- > > > > From: Rob Jarratt robert.jarr...@ntlworld.com > > > > Sent: 17 February 2022 22:38 > > > > To: 'Brent Hilpert' bhilp...@shaw.ca; r...@jarratt.me.uk; 'General > > > > Discussion: On-Topic and Off-Topic Posts' cctalk@classiccmp.org > > > > Subject: RE: Testing H745 Regulators > > > > Sorry it has been a while responding. I have been looking further at my > > H745 > > > regulators this evening. Below is what I have found and my responses to > > the > > > various questions. > > > > In summary, it looks like the rectifier may be faulty. It is marked > > NSS3514. > > > I believe it is a 35A part. Can anyone suggest a suitable replacement? > > Maybe > > > something like this: > > > > https://uk.farnell.com/taiwan-semiconductor/gbpc35005w-t0/bridge- > > > > rectifier-1 > > > > ph-35a-50v-thd/dp/2677250?st=rectifier which is rated 50V and 35A? > > > > Thanks > > > > Rob > > > > > -----Original Message----- > > > > > > From: Brent Hilpert bhilp...@shaw.ca > > > > > > Sent: 27 January 2022 03:33 > > > > > > To: r...@jarratt.me.uk; Rob Jarratt robert.jarr...@ntlworld.com; > > > > > > General > > > > > > Discussion: On-Topic and Off-Topic Posts cctalk@classiccmp.org > > > > > > Subject: Re: Testing H745 Regulators > > > > > > On 2022-Jan-26, at 3:41 PM, Rob Jarratt via cctalk wrote: > > > > > > > I am trying to test a couple of H745 regulators with a DC bench PSU > > > > > > > > and I am having some problems with testing them. > > > > > > > > My bench PSU is a twin unit so I can supply the +15V required as > > > > > > > > well as the "AC" input using 20VDC from the other half of the bench > > PSU. > > > > > The problem is that I don't think the bench PSU can supply enough > > > > > > > > startup current to allow the regulator to run. It can only supply 5A > > > > > > > > max. > > > > > > > > I have seen with the H744s that if I put too big a load on them, > > > > > > > > then they can't start because of the heavy startup current required. > > > > > > > > I can start them with a lower load and then add load once the > > > > > > > > regulator is running without breaching the current limit of the PSU. > > > > > > > > With the H745s I have tried reducing the load to see if I can get > > > > > > > > them to start, but a 10R load appears to be too much and the > > > > > > > > regulators draw the full 5A without outputting -15V. > > > > > > > > I have two H745s, both exhibit the same behaviour. I suppose they > > > > > > > > could both have the same fault, but I am inclined to think that > > > > > > > > perhaps they need a higher startup current than I can supply. Can > > > > > > > > anyone > > > > > > > > confirm this? > > > > > > 20V on a 10 ohm load: current = 2A. > > > > > > 15V, 1.5A. > > > > > > In this regulator design there is no path for more current than that > > > > > > which > > > > > > the > > > > > > load draws, aside from temporary peak currents to charge capacitors. > > > > > > If you're drawing 5A DC from the bench supply, something beyond > > > > > > 'failure to start' is wrong. I would expect this supply to operate at > > > > > > small load > > > > > > regardless. > > > > That's interesting. On the H744s I have observed that if I have a high > > load the > > > bench PSU current limiter operates and the regulator cannot output +5V, > > but > > > if I start with a lower load and then add load, it can continue to > > operate. Is > > > the H745 different to the point that I shouldn't expect this kind of > > behaviour? > > > If it is the same, then why do the H744s do this? I have tried waiting a > > few > > > moments to allow the input capacitor to charge up, but the regulator just > > > > does not start. > > > > > What is happening to the bench supply voltage? Does it go into current > > > > > > limit? > > > > > > Does this bench supply have an adjustable current limit?, so that you > > > > > > could > > > > > > run it up starting at a low current while taking measurements. Or, > > > > > > does > > > > > > the > > > > > > current respond with some linearity to varying the input voltage? > > > > > > What happens with no load R? > > > > Yes, it hits the limit, and it does so even if I have no load at all. > > > > > Are you running it for any length of time at 5A? (Sounds like a bad > > > > > > idea > > > > > > at this > > > > > > point) Anything getting warm? > > > > I daren't run it for long. I just tried running it for 15 seconds and > > couldn't find > > > anything hot. > > > > > Is the 723 socketed? Pull it and run it up while watching what happens > > > > > > around the drive transistors and elsewhere. > > > > > > If the 723 is not socketed, consider pulling Q5 or opening it's > > > > > > emitter connection. With no drive to the drive transistors, input > > > > > > current should > > > > > > be nil. > > > > > > Are any of the drive transistors socketed, so they could be measured > > > > > > out > > > > > > of > > > > > > circuit? and other R measurements made without them in circuit? > > > > > > Pull F1 to isolate circuitry. Still draws current? > > > > Well, that is interesting. I pulled the fuse and it does indeed pull in > > all the > > > current. According to the schematic, the only thing it could be is C1 or > > R1. I > > > tested C1 out of circuit not too long ago and that seemed fine. I took it > > out > > > again to be sure and C1 seems fine. R1 also seems to be fine. Which leads > > me > > > to suspect the rectifier may be bad, although some in circuit tests seem > > to > > > show it is OK. So, to be clear, I tested with the fuse out, with the > > rectifier > > > feeding C1, with R1 (3.9K) across C1. The bench PSU hits 5A when trying to > > > > supply 20VDC to the rectifier. As the fuse was removed there couldn't be > > > > anything else that is shorted. The capacitor does not charge up. > > > > This does suggest the rectifier is the problem. > > > > > Have you looked for shorts/leaks?, especially leaky junctions in > > > > > > transistors > > > > > > Q2::Q5. > > > > > > e.g. R measurements, no F1, no load R, both directions: > > > > > > Q2.B-C ? > > > > > > Q2.E-GND ? > > > > > > Q2.C-GND ? > > > > > > -15-GND ? > > > > > > Settling time for cap charge/discharge may be needed. > > > > > > In answer to your earlier question, no, the +15V is not the reference, > > > > > > it > > > > > > is the > > > > > > supply for the 723 regulator IC. The reference is the internal > > > > > > reference provided by the 723, though that internal reference is > > > > > > powered inside the > > > > > > IC > > > > > > from the +15V.
