Overview - I was given a faulty Tektronix 213 DMM/Scope for my birthday, and firstly I have fitted an option 1 capacitor to operate it from 240V mains in the UK. Thanks to the forum members who clarified the capacitor I needed! I'm back for some more advice please.
I plugged the boards back together and prayed to the gods of old technology and turned it on - no visible indications, power light etc but I immediately started to smell the bad smell, and switched it off again. I was hesitant to touch parts to try to establish if anything was hot in case of high voltage charge remaining, and the bad smell wasn't obviously coming from anywhere in particular.
So I know I need to start troubleshooting with the power supply board, but I want to be sure that I can run it disconnected from the rest of the scope without damage.
That is, if I leave the various loads disconnected. will this cause any damage to the power supply boards? Schematic here:
http://w140.com/tekwiki/images/7/7b/Tektronix_213DMM_Battery_Charger_and_Power_Supply.jpgI plan to disconnect the secondary power board at P420, connect 240V ac supply and measure the voltage at TP12. Assuming it is good at 330V dc, I'll then plug it back in and see if I get the expected voltages at TP4 and TP13, then work my way across the board seeing if I can find any problems.
I know that I'll need to replace the batteries, and I expect that without them fitted the low volt shut down circuit will operate. I can fake the battery voltage temporarily to ensure the circuit is operational in all modes.
The batteries in the case were 2x Panasonic NiCd D cells - rated at 4000 mAh (picture attached). I have found possible replacements in both NiCd and NiMH - see here
http://cpc.farnell.com/yuasa/1dh4-0t/battery-ni-cad-d-4ah-tagged/dp/BT05361 and here
http://cpc.farnell.com/gp-batteries/gp700dh1a1p/battery-ni-mh-d-7ah-1-2v/dp/BT01866.
The NiCd cost a bit less (isn't really the main consideration here) and have the original rated capacity - but NiMH come in up to 11Ah - so that's nearly 3x the original running time. Can I fit these as a drop in replacement? Should I look over the charging circuit and make some adjustments there - maybe to increase the charging current slightly otherwise I might be looking at a charge time of 48H!!! (the original charge time stated in the manual is 16h).
Any advice would be very gratefully received.