Replacement ballast for my EPROM eraser - Page 1
Forum section: electronics / repair

author: brandon.arnold
author_rank: Contributor
timestamp: May 04, 2025, 07:46:12 pm
content: Hi all. This is the ballast in my B&K Precision brand EPROM eraser, model 851. The bulb (which I was able to source) is G10T8, and the starter is FG-1E (10W-30W).I was trying to get the old thing going again. After replacing the bulb and the starter, it was working for a couple of tries. The starter and bulb would flicker a few seconds, and then the bulb lit and would run indefinitely.The third time, it flickered a while and then threw the GFI circuit it was connected to. After resetting that, I couldn’t get the starter and bulb to work again.I’m not sure where the fault could be but I would like to replace the ballast next. Can anyone suggest a replacement for this part? And any suggestions are welcome. (Except the suggestion to go to LEDs lol; no thanks, that’s another post.)

author: CaptDon
author_rank: Super Contributor
timestamp: May 04, 2025, 09:40:19 pm
content: If you can find a Robertson Transformer 4-6-8 watt universal ballast it should work. I don't have a part number for you but they are very common. That ballast is nothing more than a two wire inductor. It is not sophisticated. Don't know why it would trip a GFI unless it was the spike noise from the starter or it truly does have ground leakage. I would think you could find an exact replacement on Ebay?

author: Ian.M
author_rank: Super Contributor
timestamp: May 05, 2025, 12:16:12 am
content: Magnetic ballasts are pretty simple and as CaptDon has already mentioned, that type is the simplest - just a two terminal inductor. There are only three possible ballast faults:Its insulation can fail to the core, giving a short (or leakage to ground) This is easily tested for - disconnect the wires and test the insulation resistance (preferably using a HiPot tester) between either terminal and the baseplate (scrape a little paint off).Open circuit or high resistance - test for resistance across its terminals, I expect under a hundred ohms, anything over a couple of hundred ohms is definately faultyShorted turn - this one's hard to test for without the equipment to do a ringing test. If it gets really hot or a good lamp's running current is excessive its probably bad.As it has a plastic coil former, and doesn't look 'cooked', a short (or leakage) to the core is extremely unlikely. If you don't have a HiPot tester, disconnect (and insulate) the wire going to the tube, confirm the other wire is Line from your mains supply, not Neutral, and confirm the unit is properly grounded, then power it up. If the GFCI doesn't trip, the ballast doesn't have a ground fault, so you should look elsewhere for a fault. If your 'GFI' is actually an AFCI, its possible the normal action of an electro-thermal starter is actually tripping it. You may need an appropriately rated electronic starter.Here's more than anyone needs to know*about fluorescent lamp circuits:https://lasersam.org/sam/flamp.htm* Since their mercury content has got fluorescent lamps removed from the market in many countries.

author: brandon.arnold
author_rank: Contributor
timestamp: May 07, 2025, 08:35:23 pm
content: Hey guys. Thank you very much for the feedback, Ian.M and CaptDon. The device is working, now. I ended up replacing quite a bit.I found that not only did the GFI circuit reset, but the eraser's built-in fuse blew (0.25A 250V). So I decided to just replace most everything.I was impatient and got a Robertson F32T8 electronic ballast, so I may be right back here replacing with one specifically rated for 10W. (The bulb is G10T8.) But for now the whole circuit works.I attached some drawings of the before and after circuit as well as the finished installation of the new ballast and the parts that ended up failing in the process of reviving this old thing.

author: CaptDon
author_rank: Super Contributor
timestamp: May 08, 2025, 12:26:57 am
content: I should think that ballast is 32 watt rated. It's going to be brutal overkill to a 10 watt bulb.

author: brandon.arnold
author_rank: Contributor
timestamp: May 08, 2025, 12:45:18 am
content: You are not wrong, but it actually supports a range, 17W-32W. Well, anyway, I called it out above; don’t be like me, get the right one.