Hi, I already have a working one of these meters which I use all the time but I saw another one on eBay which was sold as spares fairly cheap (£35) which arrived the other day; so I thought I would try and repair it.
When you power it on there are no indicated fault codes, but the issue is whatever mode of measurement the meter is in the display will flash "- OL -" or overload. (see pic below)
I checked the main voltage rails and they seemed ok; I probed over the relays and I could see the switching signals coming in and out of the buffer chip from the controller logic; one of the relays wouldn't trigger when i clicked through the modes but perhaps it was part of the null feature, or something else.
Well, after a shocking afternoon literally with this unit (lol don't ask!) I thought I managed to narrow it down; so I just reheated a load of pins around the suspect area and it started working! The calibration looks not too bad at all; the sticker on it says the last calibration was 2016 so that was good.
Well, the story didn't end there! it looked like I was somewhat premature in my celebrations!!, later that day it started glitching out again with the same issue! I initially started to think it might be a component acting intermittently - that would have been a real nightmare to find and fix; but what I found was after tapping the board in various places I found that it would fix itself, then fault again.
So, I carefully tapped each component and narrowed the issue down to near the front edge of the board; after flexing the PCB very slightly one way I could make it work and by flexing it the other way it would fail; so, I started looking for any broken tracks on the board; the PCB looked ok ( i need a pcb inspecting tool i think!), so then I started tapping each component, then, all of a sudden I noticed the leg on a resistor had separated from the body - so I removed it out and replaced it; I tested a few resistors of the same value from a batch to get a closer match to the original one, but the broken resistor was certainly the root cause of the overload issue.
Quick test
Some useful bits are if your TIL117 chip is labeled IC307 then you have a later model 7150 (serial 300921 onwards), and if it's labeled IC306 then you have the older version; there are some very subtle differences in the power rail circuit if you check the circuit diagram. I'll have to check my other meter to see if it's a later one.
I left the meter running most the evening and it was fine so I will leave it on for a few days to give it a bit of a soak test; I know there is a lot of talk about these meters blowing up etc if the filters fail; I did come across someone who suggested that PAT testing doesn't do these filters any good; I have emailed Shaffner directly to ask them about possible issues and PAT testers on legacy electronics equipment with regards to the FN 370 type, not sure if I will get a reply. But I wondered of the ones that failed very badly, what size/ type of fuse did they use in the mains power lead feeding the meter; most people? use these common power leads interchangeably between different devices - could they have minimized the damage and fire risk by using a smaller more suitable fuse and labeling it for the solartron maybe?
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