Chemistry Electronics Services
ARCHIVE OF REPAIR TRICKS, USEFUL INFO, ETC.

BRUKER BLMH60 TYPICAL REPAIR, DEAD MOTOROLA CA5800C
FAILED RF AMPLIFIER BLOCK INSIDE BLAXH50, BLARH100

Symptom: the high channel of your Bruker NMR BLAXH50 is only putting out 15watts (or even zero watts) at 500MHz, while other sections work fine. I've now done more than one of these repairs. The weak point is Motorola part CA5800CS. It's a wideband amplifier module, an epoxy cube on a copper block with gold wires, +15dBm gain. It apparently dies of old age, and the failure may also cause the large adjacent 82ohm 3W resistor to char, and the 0.01uF bypass cap to crack.

In the recent past these obsolete parts were long gone from all suppliers. If you could locate a CA5800, it would sell for several hundred bucks. But recently (2014) many China suppliers are selling these on eBay for about $15. They look slightly different and have a 2002 datecode rather than 1997. Replaced and working so far, fingers crossed.

Note that the schematics and block diagram for BLMH60 are indeed in the Bruker BASH service handbook cdrom. Look for "List of Manuals," the file called contents.html. It's on that list under BLAXH 300/50 500-600 MHz (TM), filename /pdf/z31265.pdf.

Several other Bruker units contain one or more CA5800C devices. If these tend to fail after ten years, check for this problem during failures in the following pulse amps:

• BLAXH50
• BLAXH100
• BLAXH300
• BLARH100