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I just acquired a pristine condition 2465B with its tamper stickers still intact (last cal was 2010).

The scope is an older serial number (134049) manufactured in the Guernsey Islands in 1988. The A5 board has through-hole electrolytics. All of the caps (and everything else for that matter) look very clean and in good shape. It does not appear that any attempts have been made to repair this scope.

When it powersup, the LEDs all illuminate, then a relay clicks, then lighting up in sequence, CH1, CH2, CH3, CH4, ADD, INVERT, VERT (in the TRIGGER section). After that the only LED that remains illuminated is ADD. There is a jittery and blurry message that reads "DIAGNOSTIC: PUSH A/B TRIG TO EXIT" and "TEST 05 FAIL 40."

When I exit the diagnostic, I get a reasonably focused trace for Channel 1, but I can't position it above the center graticule line, and when I position it below the line it gets progressively wider. Same for Channel 2. Channels 3 and 4 will position all the way to the top, but only about two graticule lines below the center. The readouts are blurry and jittery and are at the 3rd graticule line down from the top and at the 3rd graticule line up from the bottom. Changing the readout intensity also changes the focus of the readouts.

I've read about the TEST 05 FAIL 40, but the caps on the A5 board are not SMD and they look fine. Might they still be the cause of this?

Any and all help much appreciated!

Thanks,
Stan

Thanks for the reply, Chuck!

Here are the power supply voltages and ripples, as measured at J119:

-15 measures -15.001 V with 0.99 mV of ripple
+5 measures +4.991 V with 33.86 mV of ripple
-15 UNREG measures -18.293 V with 28.1 mV of ripple
+10 REF measures +10.009 V with 1.34 mV of ripple

-5 measures -2.899 V with 8.71 mV of ripple <<

+15 measures +15.010 V with 0.58 mV of ripple
+87 measures -+86.799 V with 1.08 mV of ripple
+42 measures +42.484 V with 1.10 mV of ripple

-8 measures -4.291 V with 30.4 mV of ripple <<

+5 measures +4.978 V with 0.96 mV of ripple

So clearly there is something wrong with the -5 and -8 supplies. I measured the unregulated output of the -8 supply at J232A Pin 5 (interconnect between the A3 and A2A1 boards), and it was -8.3. When I removed the interconnect, the voltage jumped up to -16.5.

Is it reasonable to assume that the problem may well be with the filter capacitors on the A2A1 board? I suspect that a shorted or leaky C1350 may be pulling down the -8 line, and thereby pulling down the -5 line through CR1334.

The next step is to remove the LVPS. I plan to do that later today.

Thanks,
Stan

All seems to be well now. I found a high ESR 100uF cap on the A3 board in the -8v circuit (C1102). I ordered a bunch of 100uF/25V 105C caps and replaced all of them on both the A3 and the A2A1 boards. I also replaced the four radial electrolytics on the A5 board.

Now the scope powers up without errors and seems to be working properly.

I plan to replace all of the potential problem caps in the scope, but in some cases I'm having trouble finding the exact value replacements. For example, would there be a problem replacing the 250uF/20V caps with 330uF/25V caps? I know the tolerance given in parts list suggests that this would be acceptable, but I wanted to ask the opinion of those who have more experience with this than I. (Thanks, Chuck!)

Stan

Looking at your precise ripple values gives me the feeling
that you simply measured them using the AC(RMS) function of
your DVM. If that is the case, the true P-P ripple is more
like 2.8 times the values you measured.

When a -8V DC signal with a lot of ripple is measured on a
DC DVM, you tend to get a reading that is an average of the
ripple.

I would say your first task should be to recap your supply,
all of your ripple values look too high. In some cases, way
too high.. remember 2.8x RMS -> VP-P, and tek's specs for
ripple are in VP-P.

As to the voltage jumping up to 16V when you removed the load,
that is normal, as the series regulator can leak enough current
to make the incredibly light load your DVM presents, all the
way up to the unregulated supply's value.

-Chuck Harris

Stan wrote:

Thanks for the reply, Chuck!

Here are the power supply voltages and ripples, as measured at J119:

-15 measures -15.001 V with 0.99 mV of ripple
+5 measures +4.991 V with 33.86 mV of ripple
-15 UNREG measures -18.293 V with 28.1 mV of ripple
+10 REF measures +10.009 V with 1.34 mV of ripple

-5 measures -2.899 V with 8.71 mV of ripple <<

+15 measures +15.010 V with 0.58 mV of ripple
+87 measures -+86.799 V with 1.08 mV of ripple
+42 measures +42.484 V with 1.10 mV of ripple

-8 measures -4.291 V with 30.4 mV of ripple <<

+5 measures +4.978 V with 0.96 mV of ripple

So clearly there is something wrong with the -5 and -8 supplies. I

measured the unregulated output of the -8 supply at J232A Pin 5
(interconnect between the A3 and A2A1 boards), and it was -8.3. When I
removed the interconnect, the voltage jumped up to -16.5.

Is it reasonable to assume that the problem may well be with the filter

capacitors on the A2A1 board? I suspect that a shorted or leaky C1350 may
be pulling down the -8 line, and thereby pulling down the -5 line through
CR1334.

The next step is to remove the LVPS. I plan to do that later today.

Thanks,
Stan