[Test-Equipment] Next Issue Test-Equipment Digest, Vol 121,

[Steven Bender]

Hi,

I’m new so excuse me if I don’t phrase this quite properly.

I’ve got some older pieces of test equipment that are partially working, or not really working, and if anyone knows more about them and can help, I’d certainly like to hear back from you!

Unit #1 and #2  RCA / VIZ Model WP-30 this is an isolation transformer / variac for 0-5 Amps with 2 Panel Meters.  It is supposed to have a variable current adjust so you could set it up to “trip off” when the Unit Under Test pulls more current than what the control is set for. The limit control is neither calibrated nor exact, but I gather it is supposed to trip at approximately 1 Amp, 2 Amp, 3 Amp, etc. at the various lines on the control and light the "Overload led". This trip control doesn’t work on either of my units.  I’m guessing there is a Triac, Diac, or SCR that gets triggered (it may be open now) but I don’t have the schematic.  If anyone has the schematic, or a working knowledge of how that circuit works, some info would be very helpful.  One unit the pointers are missing, I’d like to convert it to digital readouts for Voltage and Amperage has anyone done that?  I think I saw one like that once.

Item #3  Sencore PR-570 - similar to above, but smaller unit 3 Amps made later since it has two digital readouts. My unit appears to be thermal, it works, but then some functions stop working after about 45 to 60 minutes. Has anyone seen this problem, or have any ideas - other than sending it back to Sencore (too expensive) or resoldering everything!

Item #4  Sencore TC-28 Hybrider Tube Tester incorrect switch settings in the particular revision of the tube manual caused the unit to show all 7119 tubes as BAD, and then after five tubes tested at those settings, the power transformer blew out.  Does this TC-28 power transformer have a thermal fuse?  Spoke to Sencore about it, they disavow their Lifetime "Made Right” Policy, and say the unit is too old - they don’t have the power transformer, or documentation, or any information on it.

Item #5  AMBER 3501 Distortion and Noise Analyzer - These units have many variations. Some have added option boards for a Model 331 Step Frequency Generator with a six digit LED Display and Stereo Matrix Switching unit permanently attached to the top cover; or optional board for IMD tests, optional balanced inputs, optional internal Lead Acid Battery, internal toroidal power transformer with IEC-320 NEMA Socket, or socket for an external wall-wart power transformer. 

In either case, the power transformer powers a linear power supply, which feeds a switching power supply, that powers the circuit boards.  The linear supply can be the full length of the back panel or the half length type. Confused yet? Units were Made in Canada, right?  The linear power supply also charges the lead acid battery, if it is present - which takes up space - making the power transformer external. Now you got it?  Anyone know what is most likely to go wrong with this set - any version. Mine… 3501 with the Model 331 Step Frequency Generator, and LED digital display, when powered up, shows a weird number (like 129123) on the LEDs no matter what the setting of any of the switches on the 331 unit.  I have no documentation on the Model 331, any help appreciated.

I’d also like to convert the internal “Battery” to a few of those flat lightweight Li-PO flat batteries as found in various Android Tablets; or the round 18650 rechargeable 3.7 Volt Lithium-Ion Batteries (four in series). Either of these would be about 8 lbs. lighter than the lead-acid battery and would last about as long as the original did.

Item #6  DRANETZ 656 Disturbance Waveform Analyzer - This unit seems to work, at least the built-in CRT works, Printer works, has two floppy drives for 3.5” disks, also has a leaking Nicad Battery inside, and "four channels” for input.  I could use a Manual / Schematic, I’m not too sure about how to use it. Found nothing on the Dranetz web site about this model.

Thanks,

Steven