Recent content by Nama

Hi spiceminer, Much thank for your reply to this thread, and also for your offline communication. Great! I will burn the ROMs and build a blueSCSI over the next few days. My MicroVAX 2000 has the standard 6mb RAM, so probably no issues with incompatibility.

Hi, yes, I thought about the MFM emulator, but it's a little expensive and I already have a couple of spare BlueSCSI boards left over from building some for a couple of my Mac systems. Yes, I am aware that I'll need to burn some new patched system ROMs, but I was also hoping that someone had...

Bit of a noob for the DEC world, but I find myself restoring a MicroVAX 2000. Thinking to build a blueSCSI and patching the system to try to get a solid state drive solution working. Wondering if anyone here has disk images that I could potentially use that they would be willing to share. Much...

Thanks for the replies...I solved it. I traced the vsync back, and back and finally found E8 (74ls20) pin 6 stuck high. , cutting that out, socketing and replacing E8 fixed the sync issue, and also I now got a cursor! Seems this board is really fussy about IC's, and I had to do a bunch of 6520...

This is my Pet in a suitcase project that I repaired and built many years ago now. At the time it was working well, but as since decided to be a pain. The system is basically a 2001 motherboard and transformer/capacitor in a suitcase with a small board mounted to the video out header to produce...

Yeah maybe...Can't think what would have caused all this damage...Maybe one component failed and then there was just a cascade of failures from that...The last thing I realised that had also failed was the 12v fan :-(

Ok, just for completeness I will wrap up this thread. John (I can't take any credit at all) finally got the PSU working! It was another monumental effort where we even considered gutting it and putting in a modern power supply. In the end John found more dead parts (mostly diodes) which finally...

Thanks, yes that's been checked. It's full wave no doubler

Base emitter voltage is 1.4v on both Q! and Q2

Ok...some more time has been spent with the PSU. So here is what it does: If powered up off 220vac mains, Q1 and the 12v regulator both get killed (these two are obviously in very different parts of the circuit!!!), Q2 seems like it never dies. If the PSU is brought up slowly using a Variac to...

the transistors in question are Q1 and Q2

Hi. I believe the schematic is shown on post #4.

Thanks for the reply. I don't think the LM1086 could handle these voltages

Thanks for your reply: “Without a circuit diagram, how did you determine that the two transistors are being used as switches?” Seems very similar to the 5155 PSU diagram found here: https://slx-online.biz/hursley/docs/5155_psu.pdf …and have been using that as a general guide. Parts in question...

...for reference the power supply is like this one: You can see the two transistor in centre bottom of the main board. can be seen here: https://commons.m.wikimedia.org/wiki/File:IBM_PC_XT_5160_Power_Supply.jpg?fbclid=IwAR2NPN_3VXYWkUz6k8_F_F71ZC65dpdtTz9c0sVGJefspS2DCG4wf-WjR3I