29 Mar
2020
29 Mar
'20
3:41 a.m.
-----Original Message-----
From: cctalk <cctalk-bounces at classiccmp.org> On Behalf Of Matt Burke via
cctalk
Sent: 29 March 2020 10:41
To: cctalk at classiccmp.org
Subject: Re: VAXmate PSU
On 29/03/2020 08:50, Mattis Lind via cctalk wrote:
Thanks Matt, I just found that bit in the documentation and realised I am not generating
enough load. I will have to add more. I did connect the 5V load because as you say it
wasn't connected.
Hello Rob,
s?ndag 29 mars 2020 skrev Rob Jarratt <robert.jarratt at ntlworld.com>:
The output specifications for the H7270 power supply are on page 9-13 of the
VAXmate Technical Description (EK-PC500-TD-001).
+5.1V - Min 6.40A, Max 10.24A
+12.1 - Min 0.17A, Max 1.37A
-12.0 - Min 0.12A, Max 0.33A
+28.0 - Min 0.45A, Max 0.55A
-9.0 - Min 0.18A, Max 0.20A
300 - Min 0.00A, Max 0.46A (for the expansion box)
I have one of those load boards from a MicroVAX 2000 but the 5V load was not
connected by default. I had to install some zero ohm resistors. The board I have
draws 1A at 12V and 3A at 5V so you will need more load on the 5V rail at
least. Thanks Mattis. I do test it with a load, although
to be honest I
forgot to do this when I took the measurements yesterday. I use a
modern-ish IDE disk and a load board from a MicroVAX 2000 as the
dummy load. I don?t know if that is sufficient.
Do you know the nominal output rating for the supply?
It might be the case that even with load board the load is uneven. But
it sounds less likely.
As Mattis has mentioned there looks to be a crowbar circuit on the secondary
side (Q2) to provide overvoltage protection. The 5V and 12V output are shorted
by Q2, which causes the primary side to sense an overcurrent condition and
shut the supply down.
I can't test it now until I get another fuse, but I am sure I didn't see this
happen, although it seems to be quite hard to tell.
Matt