Sencore SC61 Waveform Analyzer.

[chriswood1900]

This item appeared at RWB in Dec 18 and did not attract much interest so I stuck my hand up clearly so I ended up with it, it was a bit of an unknown quantity but I have a bit of a soft spot for American test gear and this was a little unusual, it was specifically designed for the TV repairman as was quite a lot of their stuff and as well as a scope optimistically quoted as 60Mhz it has a built in DVM and Frequency Counter and has several options for triggering and measuring things such as line pulses and timings.
A search round the US internet sites produced a manual so I could now understand how to use some of the features. The unit was quite grubby and on test channel 2 was unresponsive on most but not all ranges. Unlike most test equipment from the likes of Tek and HP these are built more like a TV and prone to dry joints. The low output on Ch 2was traced to dry joints on the attenuator board although getting to it was a bit of a challenge every time the attenuator was tapped or moved the output varied but it was difficult to pinpoint the exact joint that was the problem I opted to re-solder all the joints and this brought about a complete cure.
I then cleaned up the whole unit inside and out and it came up well.
One unusual feature is the DVM and frequency counter work using the selected scope input for everything but DC measurements, using a specially built probe, however these are hard to find and when they do come up for sale they are usually over $100 so that was non-starter on a cheap scope. So I set about making one, the circuit for the probes is shown in the manual so I dug out std. X10 probe and tried to take the body apart with no success, all the ones I looked at seemed the same and I was unable to open them so I decided the only way was to fit something on the outside To get the correct value to work in parallel with the scope probe I need to find exactly 13.5MΩ which I achieved with some selected 9.1 and 2 x 2.2MΩ resistor to achieve the desired value. These were then attached in series and covered in heat shrink with one end attached to the probe tip and the other to an extra lead which is threaded through the finger guard and attached alongside the probes lead and finally a small wander plug added to the other end ready to plug into the DC port below the BNC socket. The probe was then covered with heat-shrink to hold everything in place and make it as safe as possible.
The next job was to calibrate the scope for the range of values it covers as described in the manual. There are quite a few pre-sets and I worked my way through these achieving the desired accuracy until all the ranges were working correctly. Now It was time to have a play the pictures show various measurements being made, firstly a 10V AC PP voltage, then followed by measuring the line periods of a 625 and then a 405 Testcard the remaining pictures show the attenuator assembly and the probe I constructed.
Chris