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Chuck, John, The insight into 8085 programming wisdom is very illuminating. I am guessing that the 160-0459 ROM is mapped to $0000 and there are many HALT instructions (hex $76) scattered through the

Does anyone know of a link for the download of the Tek468.zip file, which contains the service ROM bin file? Thanks Tony

Heitor, What are the symptoms of the two scopes and what have you already identified as problems? Perhaps that would help us figure out ways we can help you. Please keep the symptoms of each scope

Harrison, Yes, but that action does not eliminate the rest of U550. There are other circuits in U550 that are powered through that same secondary winding of T550. That winding has 3 taps, so Pin 10

Roger, So I'm sending this letter from my PC rather than the phone. Wondering if this looks any better. I have seen my own letters from the phone since I send to all and thus getting a "Copy" Well

Alright, found a spot for -5V and checked it with both a meter and a scope, came out to -5.05V with some funky high frequency noise/ripple around 40 mV for the main body and nearly 100mV counting the

Harrison, As I recall, U550 was rather easy to remove. All the pins are somewhat obvious from the trace side of the board since they're slightly larger diameter pins. They desoldered rather easily too

I'm trying to restore a TDS6604 to it's former - hours of fun for the whole family! After a few setbacks (Overheating CPU and a flat battery on the PPC board) I have the scope working 99%. The

Hi Michael I confirmed in my shop notes, I did separate U550 and T550 by breaking the connection at T550 pin 10. After doing so F558 blew upon powering up the scope. I was looking at pulling U550.

There is one command that halts, 0166 octal, and 255 commands that don't. As I mentioned earlier, a wise programmer salts the unused memory with halts, and makes the 7th interrupt vector contain a

Hi Harrison, After reading your latest post, a light bulb went on. I did a quick search, and found that I still have a NOS U550, P/N 152-0635-00 that I bought on eBay a couple of years ago to fix a

Harrison, The problem with U550 is that it does not only contain the 1.5X HV multiplier, it also contains the DC restorer circuits and some other relevant circuitry within the module. If you look at

Hi Bert I have pulled a lead on both the C582 (2.2 mF) and the C584 (2.0 mF) caps in the 95V circuit. Both are +50% -10% Spec. The C582 read 2.40 mF Good would be between 3.3 mF and 1.98 mF. The C584

tgerbic, thank you for the confirmation on those 3 pins. So do I understand from the replies below that the processor shouldn't halt even with a corrupt Mostek ROM and I should still see pulses on ALE

Sorry about that David, to be honest I completely forgot it existed I'll get a value as soon as I'm able. On another note, yesterday on a whim I pulled out all the digital the boards, which I had

Roger, you are correct. Looking at my notepad, I penciled in L and L for 38 and 39. Not sure how this turned into both High. Must have got distracted. Pin 37 should be 2.5Mhz as it is one half the

The 8085 doesn't halt unless it executes a 166 octal instruction. 000 octal is one of the many NOP instructions, and 377 is a RST7 instruction, which calls the 7th interrupt vector location, and

The processor goes to location 0 and starts executing code on a power on reset.? Typically, the only instruction that should be at that location should be a jump to a routine that performs power on

Roget thanks. Yes, I was using an analogue scope and watching for any flicker no matter how slight. Might be time to break out the Rigol and try single shot mode. On the other hand without any boot

The 8085 has certain address locations it goes to under certain hardware conditions.? (without me looking them up, it's in the data sheet), there's one for power on reset, the hardware traps (rst