Re: 2465B - Weak Readout Intensity


Chuck Harris
 

I would say that you need a new CRT. I have replaced several
in my customer's scopes that behaved the same way.

-Chuck Harris

flanneltuba@... wrote:

Hi Folks -

I have a 2465B that I have been laboring over for a couple weeks, and have made great progress on from its initial condition, which was pretty sad—flickering speckles where the display readout should be and no visible traces. I bought it as a project, so was expecting some work, but I'm stumped on one last problem. After recapping the power supply, replacing the leaky electrolytics on the A5 board, replacing two resistors in the DAC voltage divider circuit, replacing a 74HCT00 on A5 that seemed twitchy when hit with freeze spray, programming a new Dallas NVRAM from the intact image of the original, which was thankfully still valid, and then finally running through the CAL 08 CRT adjustments, I am left with a basically working scope but one with a very dim Readout.

The main sweep trace(s) intensity is also a bit on the low side, though not nearly as dim. Increasing the intensity control beyond about half way simply causes the trace to stray out of focus rather than bringing the intensity all the way up to what would be considered "bright".

I have tried swapping U950 with one from a working 2465 with no change. I have crawled meticulously over the DAC circuit and double and triple checked all discrete parts and PCB traces, so I'm feeling fairly confident that this circuit is working, at least inasmuch as I can tell from my level of expertise, which is certainly well below anything resembling an expert, but certainly in the realm of capable and knowledgable. I have also gone through the A9 CRT power supply and DC restorer, for any obvious signs of problems or vastly incorrect voltages and found none to speak of, though I did not have the means to check the -1900v on the cathode, since I don't have a HV probe/meter.

I'm, hoping my windy description might ring familiar with one of you here, or that you might have some suggestions of where next I might next check.

Thanks in advance for any thoughts and advice.

- Scott



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