You are headed in this direction, but I would suspect filter caps that have dropped in value. At light load, they would still work okay, but at heavier loads the ripple may get so large that regulators either drop out of regulation or otherwise pass the ripple along. I have had this same symptom with TM5xxx mainframes.

Having said that, I know nothing about the guts of a ‘7904 – whether the mainframe has rectifier / filter banks or not.

Good luck –

Dan

Hi Dan

Does it have to be 300MHz

We just picked up an MS2024 for £3064, ex demo from Imex in the UK, it only has 8 preceding power ups on it, and is less than a month old, so as new and with full tek warranty and calibration sheets, and being ex demo they left a few extra’s in from the demo so we are a few hundred pounds up on what we expected.

Not 300MHz, but 200MHz four channel, long memory time, and MSO stands for mixed signal so it has an additional 16 channel logic analyser built in. You can also add modules that open up various serial and bus testing functions like I^2C, RS232, GPIB, OBD etc. And you can ask it to inspect your waveforms for anomalies which is very useful for those errors that occur when you looked away.

And it has a USB port, we also bought the network port mod that plugs in the back and allows it to sit on the network.

For higher frequencies I use a Lecroy 400MHz DSO which has GPIB, floppy drive and printer to get waveforms out. The lecroys are now available for a couple of hundred pounds, they are very nice scopes and while they might say 3dB is 400MHz it is actually just over 600Mhz on my 400MHz version and about 560MHz on my 300MHz lecroy. The only down side with the lecroy is that it isn’t as easy to drive as the tek’s are, all functions on teh tek are easy to find, but you can spend a lot of time wading the thick manual and fiddling to find some special functions on the lecroy’s.

Some also say the above tek I have is limited with its small screen, and yes it can get a bit busy with all inputs active including the logic, but it comes with a tek version of lab view so a lot can be pulled out to an adjacent PC, or you can simply plug a £100 flat PC screen in and hang it on the wall behind.

Tek do the MSO in higher frequency options but then the price goes up.

Regs Mark

Brain fade.  Was thinking the 7904 had a separate power supply fan.  You are correct the 7904A adds an air stirrer on the right hand side (when faced from the front).

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Greg

Tek was in the habit improving their equipment.  The catalog pages for the 7904 and 7904A described the specification differences.  I don’t have them at my fingertips but the “A” has greater bandwidth and faster risetimes.

As I recall, the 7904 had a fan which is eliminated in the “A” which reduced noise and eliminated a point of failure.  (Completely different power supplies between the two.)

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Greg

For work – we are looking for a relatively new (you know, a square CRT) scope, for as little money as possible.

Gotta have a USB port for saving waveforms, four channels, at least 300MHz, and digital.

Looks like this will be something like a used TDS3054C, but those are in the $6k range.

If anyone has a suggestion for something similar to the ‘3054C but less TD$, I would appreciate your opinion.

Dan