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Chuck,

Sorry, I was not at all clear, I should not have used the term "continuity" as I am using the Diode Test function on my DMM.

To be precise:

IC7 is open (infinity) in one direction (Red on Pin 2 and Black on Pin 1) and the meter reads 1.305 (volts) in the other direction (leads reversed from previous).

IC2 reads .512 (volts) in BOTH directions.

One thing that I have learned is that when two supposedly identical devices test so differently, using the same test instruments, there is a good chance that one of the two is defective.

I have also seen two posts on different web pages that have pointed to optocoupler failures on this particular power supply.

Does this alter your assessment of the situation?

I am always suspect of my knowledge and abilities, NOT questioning anything that you are trying to convey to me.

I appreciate your response and your patience.

Sincerely

All:

I have been studying this power supply all morning and doing some unpowered testing of various components in circuit.

I have two optocouplers in this circuit. They are type CNY17-2 and I found the datasheet on the parts (very simple design), no confusion for me as to how they work or their purpose in circuit. These are arranged across the "border" (for lack of a better term) between Low and High voltage sections. Pins 1-3 are on the "LOW" side, (Pin3 not connected internally) and 4-6 on the "HIGH" side on both IC2 and IC7. Checking IC7 (in circuit) with the DMM, I get continuity in one direction between 1 and 2 and infinity or "open" in the other. When checking IC2 (same component as IC7), I get continuity between pins 1 and 2 in BOTH directions. It seems to me that this indicates that the LED in the !C2 device is faulty? If so, this should prevent the power supply from working. Am I on to something here? Or am I misdiagnosing the components? This may seem a silly and very simple question, bear with me as I think this thing through. My experience tells me I am correct, but confirmation from a more experienced person or person would be very helpful. If I am wrong, what might I be missing?

Thank you in advance for advice.

Hi, there is a peculiar property with emitter followers and FET source
followers. Under some circumstances they will provide a negative input
impedance. This with a certain source impedance will start an oscillation.
To prevent this from taking place a series RC link is normally placed from
base or gate to ground. This might be a hint for you.
G?ran

Hi Chuck,

On Mon, Aug 19, 2019 at 01:58 AM, Chuck Harris wrote:

The scope has been running all afternoon with the
capacitor removed, and frankly I can't even tell it
is gone... A lot of circuitry for such little affect.

However, the anomaly continues exactly as before.

Thanks for checking that, so it's off my mind.

I agree re. Q4432, Q4440, and all of
those high resistance resistors in the focus chain.

Interesting and intriguing!

Raymond

The four rubber vibration damping fan mounts on my circa 1956 brown case 545 have disintegrated. Any suggestions on where I might find suitable replacements?

Well I suppose this sounds silly, but I just can't get over it. This thin
metal sheet inside the handle is surely tough, high tensile strength steel,
but somehow subjectively it doesn't nearly impress as the rugged 465
handle, for example. In my head thin metal sheets tear and crack. Every
7000 handle end I inspected showed some minor bending around the hole where
it pulls against the main screw.

So my question is, has anyone ever had that handle crack or snap? 7000s are
no longer costly lab instruments handled with utmost care, today we use
them in our homes, shops... They get transported probably a lot more
frequently than they were intended to, possibly against some rules which
were in power back then, now forgotten or never even known. Should the
instrument be supported by your other hand from below?

I don't use my 7104 often, but when I do I need to carry and lift it on the
table. And every time I get shivers in my feet. Some reassurance would help.

Best Regards,
Nenad F.