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Hi Michael, Dana, Roy, et al,

Unfortunately the Rockland 7530 has one massive drawback and that is what it takes to repair.

This plugin consists of 6 or 7 (I forget the details) almost full length PC boards that plugin to a motherboard located directly behind the front panel of the plugin. The metal top side and the metal bottom side of the plugin are stamped to create guide slots the boards will fit in as they are inserted or removed from the motherboard at the front of the plugin. Each of those boards has a full row of fingers that plug into their mating connector on that motherboard.

Two of the boards have fingers at their other end as well. One of these boards provides the vertical information and signals to and from the scope so it has to plug in to the interface board of the scope. The other board provides the horizontal information and signals to and from the scope so it also has to plug into the interface board of the scope. It sounds impossible so just In case you aren't sure what I was describing here it is in the simplest way possible: two of the 7 full length PC boards in this plugin have a full set of fingers at each end - one end goes into to the scope's vertical channel (the other one goes into the scopes horizontal channel) and the other end of each board goes into the plugin's motherboard which is behind the front panel of the plugin.

So in order to troubleshoot this thing you need at least two flexible extenders to get power from the scope and to get the plugin sending and receiving signals to and from the scope. That's only the beginning. You still have no way to troubleshoot any of the PC Boards since they are contained in a metal cage and there is no way to get to any of the boards.

You now need to make an extender board that is as long as the plugin so you can troubleshoot one of the PC boards by extending it OUT THE BACK of the plugin. Try to picture this in your mind: You have a 3 wide plugin where each of PC Boards is the full length (less 1 1/2" to allow for the controls of the front panel) of the plugin, and they are the full height of the plugin, and they are in a metal cage you can't stick a probe into.

In order to troubleshoot one of the PCBs you have to put it on the extender you made specifically for this plugin. This extender is just as long as the P CBoards in the plugin. This extender will mate to one of the 7 connectors on the plugin's motherboard which is behind the front panel of the plugin. Once the extender is in place you can troubleshoot one of the PC boards (sort of) by plugging it into the extender. But the entire time you are troubleshooting that board don't forget you have two very wide ribbon cables coming from the flexible extenders in the scope and you will have to reach over those clumsy ribbon cables to get to parts on the PC board you want to troubleshoot.

As if that isn't fun enough you have some very interesting and DIVERSE circuitry to deal with. For example:
* The input section has to have very low noise and have a very large dynamic range.
* The amplitude of that audio signal cannot exceed the 12-bit range of the A to D converter they use.
* 3 different filters (I think they are Hamming, Hanning, and another one) can be applied to the incoming signal to truncate it and make it appear as if it is infinite in length (a requirement of the Fourier Transform) when it obviously isn't.
* From there it is passed to a bunch of bit-sliced microprocessor chips assembled into a 24-bit computer that is running the algorithm that performs the Fourier Transformation on the incoming 12-bit samples.
* The microprocessor needs to be 24-bits wide since a 12-bit wide data word times a 12-bit wide data word results in a 24 bit product. If I am not mistaken a 12-bit word divided by a 12-bit word yields a-yields a 24-bit quotient as well. So far I have not had to troubleshoot the bit-sliced microprocessor in this plugin. Thank goodness.
* One card contains the Dual-Port RAM that is used to store the incoming data, the intermediate calculations performed by the Fourier Transform algorithm, and the horizontal and vertical display data going to the scope. It must be dual-ported RAM since the microprocessor has to juggle real-time data constantly filling one area of RAM, processing already stored data with the Fourier Transform algorithm and saving intermediate results in another area of RAM, writing out the final results to a different area of RAM. The scope needs to be refreshed asynchronously each time there is new data to display but first it has to be converted back to analog.
* The D to A converter has to combine character readout information with the results of the Fourier Transform and convert the entire thing into vertical and horizontal analog signals the scope can display.
* At this point the power supply may seem like it must be the least sophisticated part of this plugin. Far from it. This plugin needs every possible watt it can squeeze out of the 7000 scope. The specifications for the 7000 series were codified in the mid-1960s. The power supply requirements were designed to meet the needs of analog circuit designers. Digital logic was just beginning to appear on the scene so little consideration was given to its power requirements. The only solution was to convert the mainframes +/- 50VDC power and/or +/- 15VDC power to the lower voltage and higher current needed by digital logic and microprocessors. The only way to do this efficiently is with a switching supply. It is a very bad idea to put one of these in proximity to a very sensitive front end like the 7530A or 7530B has. It requires a lot of filtering to reduce the electrical noise from this type of supply. It also requires a huge amount of shielding.

To have any hope at all of ever getting one of these plugins to work you need to have two of them so you can at least swap boards to narrow down where the problem lies to a single board. Even then your chances are slim unless you have experience with the staggering array of technology these Rockland Instruments engineers brought to bear to create this plugin a full decade or more before Tek did. No wonder Wavetek wanted to buy their company.

Dennis