Another
hp 5216A arrived earlier this week, advertised as defective, on inspection I found the 150mA mains fuse blown. A replacement with a slightly lower value fuse resulted in one of the displays lighting very briefly, yep blew again.
Today I pulled the power supply board & started checking for shorted components, quickly found one of the pair of zeners for the +/-6V supplies was shorted.
![](https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/?action=dlattach;attach=1401827)
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Manual states it's a 6.04V at 2%, no other info apart from the custom part no. The other zener diode measured in at 6.01V at 5mA.
![](https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/?action=dlattach;attach=1401845)
Then I went through the drawer of 6.2V 1.3W zeners, to find a suitable pair to replace them both, I found a pair that matched at just under 6V, 10mA each. After fitting them I checked this part of the supply to verify it was working before refitting it.
![](https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/?action=dlattach;attach=1401857)
![](https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/?action=dlattach;attach=1401851)
Back in it went, along with another fuse, the lamp limiter was used and the 100W lamp left in it glowed brightly, followed by the fuse blowing again. Bugger still something wrong with it, I removed the power supply board again and changed the lamp for a 15W one & fitted another fuse, again the lamp was bright.
At this point I had a look at the power rating in manual, it gives a maximum of 20W.
No 25W lamps were in the box for the lamp limiter, so I fitted a 40W, this also lit brightly. At this point it's looking like I have another counter with a buggered transformer. I will put the 15W lamp back tomorrow & check the outputs from the secondary windings tomorrow, run out of time tonight.
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David