B&K Precision 560A IC tester repair log

Some days ago I wanted to test some RAM chips from an arcade PCB using my B&K Precision 560A tester :

For the uninitiated this piece of equipment allow you to do out-of-circuit and in-circuit testing of many ICs like TTLs,RAMs and ROMs thanks to an extensive internal IC library.I often use it during my repairs but in that day it suddenly died, no sign of life, nothing came up on display when I powered it up.For first I checked the main fuse and it was good so I decided to open the unit:

Having no schematics I started my troubleshooting from upstream checking the big transformer just after the AC input, voltages were present on its secondary coil.Following the path I figured out the AC voltages are rectified by a circuit on one of the PCBs.In particular the rectified +12V is then regulated by a couple of ‘LAS1605’ fixed +5V voltage regulators (in TO-3 package) mounted on a big heatsink for providing +5V to the circuitries on the other boards:

I probed the inputs of both and +12V was present:

As well as +5V on the output of one regulator:

But the other one was giving only +1.706V on its output, too few for correct functionality of the logics on PCB:

I looked online for buying a ‘LAS1605’ +5V voltage regulator or a compatible one but found only few at not really cheap price.Then, as a last resort, I asked my local electronics shop, they surpringsly had in stock some TO-3 ‘MC7805CK’ which is a perfect drop-in replacement (although it can deliver up to 1.5A output current against the 2A of the ‘LAS1605’ but this is not really an issue since I don’t think the tester can draw more than 1.5A during normal operation)

I pulled out the suspicious part:

I swapped the spare in and was welcomed by this :

My BK560A rised from its grave! Not too bad for a 2-euro repair! (as much as the replacement part costed…)