Tech Chat HeathKit IT-5235 Yoke & Flyback (LOPT) tester
I recently made my first purchase from the United States, they seem to have a lot more interesting Radio & Television service equipment than can be found in the UK. One thing in particular being Scan coil and LOPT testers. This Heathkit offering seemed ideal, as on the rear it stated it operates on 120V/60Hz -240V/50Hz. So the order was placed and a little over 3-weeks later, the device arrived at my door. Payment for the item, shipping, Customs etc was all sorted in one payment, all very simple.
What I found appealing about this tester is it can not only test out of circuit, but in circuit too. Rather than having to isolate components, allegedly you can test the entire output section for both Valved and silicon stages. Also Perform peak-to-peak drive voltage checks. All a little more sophisticated than the Go-No-Go of my Jabco or a simply ringing with a scope.
I'm reasonably confident as to what I need to do, to get it running on 240V instead of the 120V it was on. However, being a constant doubter, would like to just run it past you guys.
The transformer is currently looped 1 to 3 and 2 to 4 configuring the TX into 120V mode. To configure the TX to run on 240V I remove those loops and just loop the middle two, 2 to 3. Do you agree?
I have the full-service manual and will upload to the data library
Despite wiring as shown, something is amiss. It does power up, the indicator light illuminates and oddly the meter deflects negative. I wondered if it might need D.C. and A.C. calibration due to now operating on 240V. I then noticed what looks like a past burn up on R144 (220R), there should be 15V here, but there's only 500mV. Further checks reveal no 23.5V rails.It looks like I've voltage into the TX but nothing coming out at point (R) & (N). Wonder if the TX is dead.
What a shame, it looks like the TX is faulty, I've no 23.5V output from either of the secondaries. Probably why it was so cheap!
Well that was a long wait for a short-lived thread. Don't suppose anyone has a 240-24-24 TX
Hi Chris, it should be relatively easy to obtain a suitable transformer to provide about 24-0-24 volts, assuming this one cannot be repaired... I guess you can check continuity of the windings to see which is open.
But you need to find out what, if anything, caused it to fail. Maybe a short elsewhere?
As Andrew suggested, I assume both primary windings are continuous? A transformer with 2x 24V windings will be an off-the-shelf component from the likes of RS/CPC/Farnell.
New TX ordered from RS, should be here tomorrow.
I'll check before the new is installed.
PS.... When changing from 120 to 240v mains, you need to halve the rating of the mains fuse. 😉
In this case, I think a T60mA will do unless I am mistaken.
You are quite right, I'm being over cautious perhaps.
A 60mA could easily pop just by a switch-on surge.
Here's the full circuit, full manual in the library, though the cct in that is poor, hence there is a separate cct png
Found a lot more wrong, two 1N4002, diodes had failed, two 15V zeners also and R144(220R/1W) massively overheating. Turns out an LM311P was shorted. None in stock, some on order, awaiting arrival.
However, when I said "none in stock”, I was referring to none in my stock. I've ordered some, and I am awaiting their arrival.
Fed up waiting for the LM311 IC to arrive, I thought to myself, I must have an LM311 somewhere on one of my Stock PCB's. I felt the most likely candidates would be VCR or laserdisc player boads
With that in mind, the first board I located a VLP700 PSU/EHT generator PCB, would you believe it, the only IC on that board was an LM311N, what a stroke of luck. Moreover, it was socketed so an easy extraction.
It was swiftly installed into the IT-5235, again socketed and I powered up, this time the meter did not deflect in a negative direction and R144 was not overheating, result.
I then next went through the DC calibration, thankfully the unit still had its DC volts calibration sticker, so I knew it had to be calibrated to 7.36 on the 10kV scale. Result, it was spot on. Next AC calibration, that should read between 13-17V on the 30kV scale, and it does.
Simple test now, out-of-circuit LOPT test. I chose the LOPT I intend to install in the G6 this coming winter. Rotating the Ring selector, a good LOPT should ring on every setting. Happy days, not only is the Flyback test working, the LOPT is good.
Time to read the user manual to get to grips with all the other possibilities this tester provides for in-circuit testing.
Great news ! 👍
What a magnificent tester Chris!
Fed up waiting for the LM311 IC to arrive,
13-days later the LM311P I ordered for this project turned up. Oops, me thinks I made a mistake on the order, for number required, a zero where one shouldn't have been. I thought the bill seemed a tad higher on checkout, but as it was bundled in with a load of other bits, ignored it. Hey-ho, looks like I'll be sorted for comparators for the foreseeable future 🤣
You going into production of LOPT testers now Chris? 🤣
Oops, me thinks I made a mistake on the order, for number required, a zero where one shouldn't have been.
"Typical, innit? You stand here for days waitin' for a chip, then suddenly, fifty of 'em all turn up at once!" 💥