DEC H7140 (11/44) power supply revisions and general advice?
derschjo at gmail.com
Sun Oct 11 22:01:42 CDT 2015
On 10/11/15 6:19 PM, Josh Dersch wrote:
> On Sun, Oct 11, 2015 at 12:07 PM, Brent Hilpert <hilpert at cs.ubc.ca
> <mailto:hilpert at cs.ubc.ca>> wrote:
> On 2015-Oct-10, at 8:44 PM, Josh Dersch wrote:
> . . .
> Note that the "+13V" supply must also be present, and it's
> generated and referenced on the Mains side of everything.
> In summary, for the relay to activate:
> 1) The Mains is rectified and filtered to produce Mains
> +300V via bridge LNS-CR1 and caps LNS-C1,C2.
> 2) MOB-D1,D2,R1,R2 form a voltage divider / balancing
> network to produce Mains +150VDC.
> They also balance the voltage across the Mains filter
> caps (LNS-C1,C2) when in 220VAC mode.
> ** 3) Mains +150V is regulated via MOB-R3, BIB-Q6, BIB-C4,
> BIB-D11 to produce Mains +13V, referenced
> from MOB-D2 feeding ("START-UP DRIVE") the base of BIB-Q6.
> 16V zener BIB-D12 additionally clamps this level.
> 4) Mains +13V supplies 555 oscillator BIB-E2, LM393
> comparator BIB-E3b and associated circuitry. These form a SMPSU
> with MOB-T1.
> 5) The output from MOB-T1 is half-wave rectified in both
> polarities to produce BIB +12V (MOB-D6,C3) and BIB -15V
> 6) BIB +12V produces BIB +5V via regulator BIB-E1.
> 7) BIB-E3a forms a voltage level sensor with reference
> zener BIB-D13 and voltage divider BIB-R3,R4,R27 that must detect
> an adequate level on
> the Mains +300V to turn on the relay via BIB-Q11,
> BIB-E5, BIB-E4a.
> LNS = Line Supply section PDF.146
> MOB = Motherboard PDF.162
> BIB = Bias & Interface Board PDF.166-168
> ** There appears to be something inconsistent in the schematic
> here in that the base of BIB-Q6 is fed by +10V from MOB-D2, which
> would leave the Mains +13V at more like +8V.
> Am I missing something? - is there anywhere in that doc that
> explicitly declares the association between the 2-dozen
> connectors, for example, that Line Supply P1 & P2 connect to
> Motherboard J5 & J4, and that Bias and Interface Board J1 & J2
> connect to Motherboard J7 & J6?
> Awesome, thanks for the detailed writeup. Things make sense, or at
> least more sense.
> I went to take a look at the +13V supply and of *course* once I did
> things started working, mysteriously. The relay clicks over and I get
> +13V and it looks like the bias voltages are present as well. All I
> did was tack on a wire to the 10/L header pins on the bias/interface
> board (+13V)...
> So that's... good, but I have no idea what the actual problem is/was.
> Going to clean the connectors and look for cold solder joints (again
> :)) just to rule that out. I'll get a dummy load hooked up and see if
> anything happens when I throw the front panel switch.
> Thanks again, all.
> - Josh
Re-inspection revealed no cold solder joints, but I reflowed the
backplane connector pins on the Bias/Interface board pins L and 10
anyway. I reassembled everything in the chassis, hooked up a dummy load
and everything came up fine. Reinstalled the CPU boardset + terminator
and I get the Console chevron prompt after a couple of seconds and the
built-in diagnostic tests pass. So, success, of a sort. I feel like I
cheated somehow :). We'll see if it keeps working...
Now to figure out mass storage; I have an SMD controller and a drive --
let's find out if either of them work :).
Thanks again for the analysis and advice, I'm slowly figuring things out
but I think I really need to sit down one of these days and really study
power supply electronics.
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