Recent content by MattisLind

I think that the -9V is used for the ethernet tranceiver. They are usually isolated from the rest so that is why you only get good readings between those specific pins.

It is still development, for sure it is not a finished product. It does work fine to test regular logic boards. It was when it came to flip-flops I found it had problems when the load module was active. Without activating the load module it worked fine to check the logic behavior of flip-flops...

The power supply is generating the logical signal but that doesn’t imply that it is sourcing any current. The source of the logical signal and the source of the current that develops the signal is two different things. In the case of an OC bus the current source is the terminating resistors and...

It was entirely designed by Anders. He shall have all the credit. I have been with him in this project throwing ideas and testing. One interesting feature is that it can verify that the output transistor can sink the correct amount of current. It also check how much load the inputs have. It is...

The BRS-tester by Anders Sandahl works with negative logic. https://github.com/anders-bzn/brs-tester

I had a quick look at the H780 schematic since there are no known scans of the H7864 schematic AFAIK. The H780 uses N JFET. That should have the advantage that they conduct when vgs is 0 meaning that a PSU connected to the bus which is turned of will indicate a power failure. That wouldn’t...

I don’t think you understand how the Qbus works. The Qbus is a bus where drivers with open collector or open drain is connected to each bus line. The bus has terminators that pull the signal up to a level that is detected as a high level which means that circuitry in the PSU that is generating...

Strangely there are no send message button on your profile. Other users have this button.. I know it used to work but not this time? Maybe you could send me a PM?

I could use a L0006. Both the ones I have have failed. Haven’t found the root cause. First repair I fixed a bad memory chip. Then it worked some time and have died again. So useful. At least for me who have a 11/750.

This one look very similar: https://www.ebay.de/itm/146349894270 But high price. Maybe he accept a low-ball offer?

This is the card I am using. Seems to be very similar to your board. Did you configure the board correctly? Have you verified that it works in a standard PC? I had luck with the ST3491A so try with that one first. I found the jumper settings for my board: BioStar tech support was kind...

Excellent work on fixing your 11/40. This how you do it. KM11 single stepping and checking signals in the backplane. Some extender boards will probably also be needed. Then eventually you get to the tricker problem where it runs diags for some time and then crashes. Chasing faults with freeze...

It is a 1kx4 bipolar PROM. Either you make an adapter for your TL866 (or whatever device you are using. To me it looks like you already made an adapter for reading the other PROMs. Or you can wire up a small microcontroller do read it. Or get a Data IO PROM programmer of some sort. Unisite or...

Updated the EPROM to 3.0.3 but there were no difference at all in terms of behaviour. I checked all signals of the DVMA chip but none looked that suspicious, but it is hard to say when you don't have a schematic. Fat-finger method didn't give any difference to the readout so there is probably...

You are probably right regarding flanges on the corner pins. It is not solder. I will probe around the pins on the backside and then use the "fat finger"-method pressing fingers on various areas on the board while it is running to see if the readout of the looping test changes. Then I'll try to...