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REPAIR HP 8552B IF SECTION
August 2008

The HP 8552B IF Section is working ok apart from the following issues. The indicator lamp DS6 for the right hand side of the Log Ref Level control is not working. The 30MHz calibration output is not exactly within specification. Some of the final performance tests have not been done as these needed a working 8553B RF Section, which I haven't tested yet.

Front view
September 2008

The 6 Log Ref Lamps are switched from the RF Section Input Attenuation control and fed via the D-type connectors between the RF and IF Sections.

Access to the lamps is by removing the bottom cover and the 4 screws holding the front panel.

The lamps are Midget Flange T1¾ 10V 0.04A MF1240, although DS6 was replaced with a 12V version bought on eBay. Care is needed not to bend the spring plate at the base of the lamp holder.

January/February 2009

A Display fault was traced to the Unblanking output providing the incorrect signal. Access to the IF and RF Sections for maintenance is difficult. The correct method is by using 2 extender cables (11592-60015) from the 141T and 1 extender cable (11592-60016) in between the IF and RF Sections. These extender cables are available from GLK Instruments for $155 each and $215 respectively. Plus you need extender cards for the various pcb assemblies. This would be ideal but I needed a more economic method! 

My solution is to remove the 2 inner side panels from the 141T which support the IF and RF plug-ins. These panels have bends at the top and bottom which normally prevent the pcb's being extracted. Wire links can be soldered to the pcb to enable test equipment to be attached. The faulty component was transistor Q18 in the A7 Deflection Amplifier. Luckily a stock replacement general purpose BC337 NPN Transistor could be used in this application.

Initial performance tests have been done. Setting up the vertical position, vertical gain, and amplitude calibration, in log and linear modes is a bit tricky and takes some patience to get right. The remaining performance tests are still to be done.