Tony wrote: Yes, I was puzzled too when I saw those signals. I first used the Fluke 77 for a quick check. When I saw 3.7 V on TTL pins, I figured that it is either a bad signal or the signal is not DC, but some pulse. So then I pulled the D100 out. The inputs are all set to TTL, and the 'ground' I used was pin 7 of E46. And again, I was amazed too. But the output of E5 did not look like a spurious signal. The D100 gets correct through the initialisation at power up ... I know what you mean :-) The RK07 and its controller is definately complex. I was also tracing the signals back and things get quite complicated, so that is where I decided to remove the flat cable ... a hunch ? Yep, the flat cable that I used was not shielded, and about 6 meters long ... The BC06R is a "-6" version, so a lot shorter (and shielded). Regarding noise, I suspect that the print set is not 100% up-to-date, but given the quality of the drawings from DEC, I assume that I am wrong. But, pin 2 of the E46 S/R flipflop is not connected (according to the diagram). This is the D input of the flipflop, and since the clock input (pin 3) is connected to Gnd, the state of the D input is irrelevant according the data book. However, with the Fluke 77 I measure 1.55 V on pin 2. I consider not- connected input pins a bad design, but I will not tie pin 2 to Gnd or with a 1k pull-up resistor to +5V, because that pin changes voltage during reset!! BTW, I found the same signal on E5 pin 8 and E43 pin 12, so the drawing checks out on that connection :-) Now, why did I (again) not think of that!? Looking at the head movement requires you to "stare" at a screw on the head assembly and try to see the motion to a fixed part next to that screw ... Me too :-) As I have to remove the rear cover to swap :-) the terminitor for the plug/cable to the second drive, I will look at those LEDs. I only have brief descriptions (which are also on my site), not the complete source listings of the diags. But I will run the diags that require the drive (and a mounted cartridge). Ah well, I think it is just a matter of how you look at things. Without going into that subject, I'd say that swapping is for some of us the only option. Not everybody understands electronics that well as you do Tony. An educated guess when you swap *one* board is still better then tossing the stuff in the bin, because it does not work. It isn't always that black and white. And I must admit that I was tempted in swapping boards too. Now, I know that would not have solved the problem as long as the flat cable was still connected to M7904 !!! I know, this proves that measurements are the only way, but still, that is not easy for many (?) of us. I first had to search for 3 dual extender boards before I could even begin for starters ... Hmmm, now I did get into that subject! Anyway, any feedback is a drive to continue what you are doing. That counted for me, and I figured that my "thank you" also counts for you, and that everybody will appreciate some feedback! That explains the existence of this mail list and the many people that contribute to it. - Henk. This message and attachment(s) are intended solely for the use of the addressee and may contain information that is privileged, confidential or otherwise exempt from disclosure under applicable law. If you are not the intended recipient or agent thereof responsible for delivering this message to the intended recipient, you are hereby notified that any dissemination, distribution, or copying of this communication is strictly prohibited. If you have received this communication in error, please notify the sender immediately by telephone and with a "reply" message. Thank you for your cooperation.