its a switcher.
On 11/1/2015 10:37 AM, Robert Jarratt wrote: > >> -----Original Message----- >> From: cctalk [mailto:[email protected]] On Behalf Of Paul > Koning >> Sent: 01 November 2015 16:52 >> To: General Discussion: On-Topic and Off-Topic Posts >> Subject: Re: Testing H7864 (MicroVAX II) PSU With No Load >> >> >>> On Nov 1, 2015, at 7:12 AM, Robert Jarratt <[email protected]> >> wrote: >>> Some of you may recall I have a faulty H7864 PSU, which failed a while >>> ago with a loud pop, but no obvious physical damage. I replaced the >>> blown transistor (on the primary side of the large transformer), but >>> when I power it on, the transistor does not switch and there is no >>> output, so clearly there is still a problem somewhere. >>> >>> >>> >>> I have been spending some time drawing schematics for almost the whole >>> thing. I am now at the point where I intend to compare it with a >>> working one, probing each one side by side, to see up to where it >>> appears to be working. It would be awkward to have two dummy loads, >>> just for lack of suitable equipment. Does anyone know if it is safe to >>> run these PSUs with no load? Would my testing be valid without a load? >> If it has a transistor at the primary side, and a high frequency > transformer, it's >> a switching supply. Those want a load, usually. Especially the older > ones. >> If it has a laminated iron transformer, big electrolytics for filtering, > and >> transistors at the secondary side, it's probably a linear regulator > supply. Those >> don't need a load. You may want to do full testing under load to observe >> correct regulation, but for initial testing you can test them without. >> >> Linear supplies are older; I think by the time of VAX you're likely to see >> switchers (with the possible exception of first generation stuff like the > 780, I >> don't remember if those big supplies are linear or switchers). >> >> paul > > Hmmm.... Until your email I was pretty confident this was a switcher. But > your description of a linear PSU seems to fit. I have posted three photos of > the main board here: http://1drv.ms/1KQkTBp can you tell from that what kind > of PSU it is? > > The big TO-3 on the left is the one that I found had failed. The replacement > does not appear to be switching, but I don't know why. > > Regards > > Rob > > -- The contents of this e-mail and any attachments are intended solely for the use of the named addressee(s) and may contain confidential and/or privileged information. Any unauthorized use, copying, disclosure, or distribution of the contents of this e-mail is strictly prohibited by the sender and may be unlawful. If you are not the intended recipient, please notify the sender immediately and delete this e-mail.
