[cctalk] Re: Rainbow H7842 PSU Fault
On 2023-Apr-22, at 3:53 PM, Peter Coghlan via cctalk wrote: On 2023-Apr-22, at 1:07 AM, Rob Jarratt via cctalk wrote: >> This seems to be because I measure a steady 0.6V on pin 6 of the transformer >> (p4, PSU Sheet 3). I just can't imagine where it might be coming from as the >> chopper won't be running. I had previously removed the transformer and there >> are no shorts between the pin 5-pin 6 winding and any of the other pins on >> the transformer. I checked all the DC outputs of the PSU when powering the >> 7812 from the bench, both on a working PSU and the non-working one. They are >> all at zero except the -12V output on the non-working PSU, which is +0.6V. >> But the voltage can't come out of nowhere. > > I've looked at it some more. On page 5 (control module sheet 1), at the > non-inverting input of E1b, there is a 75k resistor and 16k9 I think? > resistor between -12V and V2 which is derived from Vstart. Perhaps this > would account for the +0.6V? > > (Ignore what I said earlier about the possibility of one of the two diodes > connected to pin 6 of the transformer being shorted. The 51 Ohm (or is it a > 5 Ohm?) resistor across one of them would look like a short compared to 75k.) Following on Peter's observation above, note that under normal (as opposed to test-bench) operation, a limited -12V is supplied at startup by the same little mains transformer that supplies VStart (schematic: PSU sheet 1). This startup -12V would appear to be or may be required to bias things correctly for startup to proceed. It follows that the -12V current-sense shutdown being observed is not (necessarily) part of the fault being looked for, but just a consequence of the absence of the -12V startup. Also, minor note: not indicated on the schematic is the power supply pin connections for the comparator ICs (E1,2,3) (or I haven't spotted them). Presumably the +supply is VStart, but you might check and record whether the -supply is GND or is it -12V (and check all 3 ICs).
[cctalk] Re: ESDI drive imaging
On 4/22/23 17:14, r.stricklin via cctalk wrote: > > I can’t say that’s been my experience. I guess I've led a sheltered life. I will say that some ESDI controllers do have a bewildering variety of configuration options. And the Q for the DTC 6280 does confirm your experience. http://www.franken-online.de/ymmv/files/DTC_Q So, I spoke too quickly. Nevermind. --Chuck
[cctalk] Re: ESDI drive imaging
> On Apr 22, 2023, at 4:44 PM, Chuck Guzis via cctalk > wrote: > > On 4/22/23 15:18, Dennis Boone via cctalk wrote: >> I think I know the answer to this, but just in case: >> >> Is there a way to image ESDI disks other than to hook them up to their >> usual host controller and use the host? E.g. for MFM, I'd grab the MFM >> Emulator board. > > In my experience, you can use any ESDI controller--the drive has much of > the logic on it, similar to IDE, but not quite as integrated. I can’t say that’s been my experience. ok bear.
[cctalk] Re: ESDI drive imaging
On 4/22/23 15:18, Dennis Boone via cctalk wrote: > I think I know the answer to this, but just in case: > > Is there a way to image ESDI disks other than to hook them up to their > usual host controller and use the host? E.g. for MFM, I'd grab the MFM > Emulator board. In my experience, you can use any ESDI controller--the drive has much of the logic on it, similar to IDE, but not quite as integrated. --Chuck
[cctalk] Re: Rainbow H7842 PSU Fault
> > This seems to be because I measure a steady 0.6V on pin 6 of the transformer > (p4, PSU Sheet 3). I just can't imagine where it might be coming from as the > chopper won't be running. I had previously removed the transformer and there > are no shorts between the pin 5-pin 6 winding and any of the other pins on > the transformer. I checked all the DC outputs of the PSU when powering the > 7812 from the bench, both on a working PSU and the non-working one. They are > all at zero except the -12V output on the non-working PSU, which is +0.6V. > But the voltage can't come out of nowhere. > I've looked at it some more. On page 5 (control module sheet 1), at the non-inverting input of E1b, there is a 75k resistor and 16k9 I think? resistor between -12V and V2 which is derived from Vstart. Perhaps this would account for the +0.6V? (Ignore what I said earlier about the possibility of one of the two diodes connected to pin 6 of the transformer being shorted. The 51 Ohm (or is it a 5 Ohm?) resistor across one of them would look like a short compared to 75k.) Regards, Peter Coghlan.
[cctalk] Continental 50 Pin connector vs. AMP 200276 50 pin connector - same?
I have an HP 2875B paper tape drive that I want to interface to. It has a 50 pin block connector (using well under 1/2 the pins). The connector manufacturer was Continental. I have already discovered, the hard way, that it is not a winchester connector - the pins on the 50 pin Winchester connector I just obtained via ePay that otherwise fits are too small in diameter and won't make contact. I *could* increase their diameter using solder - but -- yuck. The other connectors of this sort I am familiar with that have the same general overall size and pinout were made by AMP. Does any one know if the AMP connectors and the Continental connectors would be compatible? Thanks. JRJ
[cctalk] ESDI drive imaging
I think I know the answer to this, but just in case: Is there a way to image ESDI disks other than to hook them up to their usual host controller and use the host? E.g. for MFM, I'd grab the MFM Emulator board. Cheers, De
[cctalk] Re: Rainbow H7842 PSU Fault
> > This seems to be because I measure a steady 0.6V on pin 6 of the transformer > (p4, PSU Sheet 3). I just can't imagine where it might be coming from as the > chopper won't be running. I had previously removed the transformer and there > are no shorts between the pin 5-pin 6 winding and any of the other pins on > the transformer. I checked all the DC outputs of the PSU when powering the > 7812 from the bench, both on a working PSU and the non-working one. They are > all at zero except the -12V output on the non-working PSU, which is +0.6V. > But the voltage can't come out of nowhere. > Is the -12V output connected to it's load while you are testing? If so, perhaps there is a path through the load to the the +12V or +15V supplys available elsewhere which would forward bias the two diodes connected to pin 6 of the transformer giving you a small positive voltage at that point. (I would have thought it would be a bit higher though, depending on the type of diode. Neither of the two diodes is shorted, is it?)
[cctalk] Re: Magazine no longer in print
My "answering the call of nature" standard reading was EDN. Sadly, it and Electronic Design are no longer published on dead trees. --Chuck
[cctalk] Re: Magazine no longer in print
Juiced.GS is still publishing, with new a new issue delivered each quarter. I subscribe and am always happy to see the latest issue delivered to me by the post office. But I've never seen a copy at a newsstand or book store. https://juiced.gs/ "Juiced.GS is a quarterly print magazine devoted to all models of Apple II computers, featuring exclusive reviews, interviews, and tutorials for all Apple II users." -- Ron
[cctalk] Re: Magazine no longer in print
Well still in print is Linux Journal and Linux Format. Ken On Sat, Apr 22, 2023, 1:02 AM Tarek Hoteit via cctalk wrote: > Funny you mentioned Brave New World. Just two hours ago I bought the book > at Target. What a coincidence > > Regards, > Tarek Hoteit > > > On Apr 21, 2023, at 9:53 PM, Chuck Guzis via cctalk < > cctalk@classiccmp.org> wrote: > > > > On 4/21/23 21:08, Doug Jackson via cctalk wrote: > >> That's the crux of it. > >> > >> Without advertisers magazines are too expensive. As advertisers needs > >> change they move to diferent media. > >> > >> It's frustrating. But part of the world in which we live. > >> > > > > Add to that, newspapers in print, broadcast TV and radio. > > > > Brave New World. > > > > --Chuck > > > > >
[cctalk] Rainbow H7842 PSU Fault
As some of you may be aware I am trying to find a fault in a Rainbow H7842 PSU. I am using Tony Duell's schematic from here http://www.bitsavers.org/pdf/dec/rainbow/duell_schematics/psu.pdf. I have been testing the Control Module by using a bench PSU to supply 15VDC to the input of the 7812 regulator (p2, PSU Sheet 1). My diagnosis shows that the control module is shutting down the PWM (p6, Control Module Sheet 2) because it is detecting an overcurrent in the -12V side (E3d on Control Module sheet 1, although I have determined that it is actually E3c). This seems to be because I measure a steady 0.6V on pin 6 of the transformer (p4, PSU Sheet 3). I just can't imagine where it might be coming from as the chopper won't be running. I had previously removed the transformer and there are no shorts between the pin 5-pin 6 winding and any of the other pins on the transformer. I checked all the DC outputs of the PSU when powering the 7812 from the bench, both on a working PSU and the non-working one. They are all at zero except the -12V output on the non-working PSU, which is +0.6V. But the voltage can't come out of nowhere. I am stumped and would appreciate any suggestions. Thanks Rob
