Seaward PAT 2000I

[Alistair D]

I have just repaired a Seaward PAT 2000I I was given a year or so ago. The problem was that most of the keypad was dead. That was caused by a faulty 4053 chip connected to the keypad matrix.

The problem I am left with is that if I power the tester up in less than 5 minutes after a power down it will often come up with the message "VOLTS ON NEUTRAL! PRESS # ONLY IF SAFE" Pressing the # key clears the message and then everything works fine. According to the manual this should only happen if there is greater than 50V between N and E. I am happy that this is not the case on any of the sockets I have tried it on.


Does anyone else use one of these testers? Does it exhibit the same characteristic or do I have another fault?

Al

[VintageTest]

Hi all,

I realise that this is an old thread, but wondered if I could revive it? I bought a Pat2000i years ago and , after an immediate fiddle, with the same message as my countryman's about the neutral being live, I stuck it under my workbench. But now, I'm repairing more old Tek, HP, Solartron, Datron etc kit, I felt it might add a bit of added value if I could say 'calibrated AND PAT tested' in my ads. Seaward are not particularly helpful, saying that it's a discontinued model - nobody still here who knows about it' etc. So . . . I dragged it out and powered it up. 'All settings lost . . .', or something of that ilk came up and I thought 'great, just a battery somewhere has failed'. I found said battery inside the keyboard - I'm sure I remember someone asking how to replace this - and duly replaced it, having de-gunked the surrounding area that the corrosion had touched - and powered it back up. Hey-ho - the same message about "volts on neutral! Press # only if safe" Pressing # does nothing. Does anyone have any details on this old box? I'd love to use it, seing it's actually newer in vintage than most of the kit I work on, but still so old it's obsolete!

Cheers,
Mel

[FIXITNOW]

according to the manual page 13 http://www.seaward.co.uk/downloads/PAT%2...21A555.pdf

it may do this
power up may the unit may display "VOLTS ON NEUTRAL! PRESS # ONLY IF SAFE"

[Alistair D]

Very interesting Mel, mine is in the same condition bar for the  fact that from cold the volts on neutral message can be cleared. It will stay away for a few minutes then return. Cycle the power and the message remains. Wait 20 mins and the clear spell returns.

When I first acquired the tester very few of the keyboard keys worked. This I traced to a faulty CD4052 on the keyboard PCB. As far as I remember the Neutral fault only appeared after the chip was replaced. I did remove the backup battery while working on the board so also got a message about lost settings/sequences.

The 4052 chip seems to cover the keyboard matrix, the bus to the main unit and the analogue voltage from the base unit that measures how many volts are between the neutral and earth. This voltage seems to be added to one of the bus lines and is measured when the line is at logical zero. I may be wrong here but without a schematic fault finding is a bit hit and miss. There is a bit more information here. https://www.vintage-radio.net/forum/show...p?t=130980 One point of note, the 4052 sits right beside the battery so perhaps you still have some conduction on the PCB.

I do wonder if the associated PC software package has a way of restoring the missing setup but with the neutral fault still present and the cost of the package I am not prepared to go down that path yet. Currently the tester is back on the roundtuit pile and is waiting for me to develop enough enthusiasm to have another look at it. Add to that that I already have a working PAT tester then it might be a while.


Al

[Alistair D]

Finally the Seaward reached the top of the round tuit pile. After further checking I was totally convinced that the 4052 chip I had fitted was either faulty or incompatible with the circuit. The original chip was a 4052B and all I could find at the time was a 74HC4052. Changing the device is no mean feat as it is a surface mounted SOIC part so it was kill or cure time. Luckily I managed to do the swap and not damage a single pad.

After refitting the backup battery a long soak test confirmed the volts on neutral fault had gone. Not only that the missing setup message had also cleared. I'm pretty sure that this message was more to with the battery being flat rather than the original problem.

Now for the Megger PAT4 that reports 1.4mA leakage during a run test when there is no leakage present. Alas service info is non-existant on the net.

Al

[ppppenguin]

74HC4052 is not always a replacement for 4052B. The original 4000 series part is rated up to +/-15V supply (18V in extremis). The 74HC part is only rated to +/-6V. The HC parts also switch much faster and have lower "on" resistance.

If the supply to pin 16 of your part is less than +6V (and less than -6V to pin 7) then your HC4052 should be OK. Otherwise it's likely to have a short life.

NB: The 4051/2/3 and HC/HCT parts all have a -ve supply pin (pin 7) that's often connected to 0V. It's useful when using them to switch bipolar signals with ordinary logic controls.

[radioman]

Well done Al  
I've got loads of 4052B in SOIC package here... (in fact many hundreds of logic and other IC's and types).
I don't remember you asking for any ?

Andy

[Alistair D]

It is all cased up now and I really don't remember what the supply voltage was to the 4052. I'm pretty sure the -ve supply was 0V. All I can say is lesson learnt.

Thanks Andy it really was a case of man over machine. 

I normally go a scrounging for  bread and butter parts but I will keep you in mind in the future. 

Al