Are you sure that the 464 has a 'power' light? I can't find one in the manual and the coloured sleeve on the on/off switch that is visible in the On position often means that there isn't a specific po

The manual shows the wiring of the two scale illumination bulbs on the power supply schematic immediately following '<16> CRT Circuit'. Page 6-3 of the manual shows the components needed for the calib

A second thought - if the voltage you measure on +6.5V is only a volt or two then there must be a significant current drain since you just have the resistive voltage drop across T490 primary and one f

I second Dave Holland's reply. When I first tried to remove a 212 from its case it was reluctant to come out in one piece without distorting the joints where the four sides join together. It is quite

It's not directly part of your question but you will find that the 7B53A is not the ideal timebase plugin for the 7904. The 7B53A was designed for the 100MHz scopes which have a longer delay line and

The charging and discharging currents for the timing capacitor have to pass through the switching circuitry of S155 so bad contacts there will stop the triangle generator working and the other wavefor

Nothing like as extreme as yours, but I had a 485 with a diffuse glow over about a quarter of the screen area on the right side. It varied with intensity control but not anything else until I noticed

Certainly some other vendors used GR874 125ohm connectors because their intended use was to preserve bandwidth into a 519. I remember a TRG manufactured planar photodiode with a 125 ohm connector used

Correction - R1101 and the emitter of Q1107 may be sufficiently low impedance that the unblanking signal does not show up well as a voltage signal. Check the collector of Q1107 or farther down the Z a

Try turning the readout off and probing R1101 on the Z axis board with one of your working scopes looking for the unblanking signal. If you don't see the unblanking, try adjusting the grid bias R1261

Colin, Can you not eliminate the mechanically operated switches eg S490 by either removing the single wire from its mating pin or solidly jumpering it to ground so that it is definitely open or defini

My comments about cathode voltage regulation were based on seeing a similar problem (and fixing it) in a much lower bandwidth scope without PDA. I hardly ever use my 7904 at low sweep speeds, but lo a

To my eye each of the shadow peaks and troughs of the sine wave lies on a straight line joining the real peak/trough to the CRT centre, but farther out. This should be very obvious at say 100msec/div.

On my 7B92A, the microswitch near the front panel is connected by a single wire to P911 on the interface board. P911 is to be found on schematic <4>, 'Delaying Sweep', near the top right corner. It is

Is the Y scaling per small division (+/- 5 within the box) or something else? Either way it doesn't look like the -5V is decaying to 0V and is Ch3 inverted? There is a very clear signal on LIMIT which

In one of your earlier posts you said you had seen spiking behaviour on pin 3 of U1624. This will drive larger spikes from the output pin via Q1614 and C1602 into the protection circuitry and can very

If you really have a short circuit from -5V to ground (eg a failed tantalum capacitor) you don't need to power up the scope, it should be obvious with a resistance measurement. Schematic <17> shows th

If the readout displays are still in the correct horizontal position then the fault is probably before the horizontal amplifier. Can't be more precise without knowing what mainframe is in use. Roger

Following on from Adrian's point, the 7B92A manual shows all the decoupling capacitors are preceded by the components labelled 'LRnnn' which are inductors wound on the body of a carbon resistor of may

When it dies does it bring down the other plugins? If they continue to work it is unlikely to be a tantalum cap across a power rail. Once tantalum caps fail they usually stay short circuit but I suppo