Robin model 3001 - UK Vintage Radio Repair and Restoration Discussion Forum

WaveyDipole · 20th Jan 2020, 2:57 pm

I posted a request on EEVblog but had no luck so I guess this is a long shot. Does anyone have a circuit diagram for a Robin 3001 insulation tester or similar model or know where I can get one please?

The low ohms function seems to work fine but the 500V and 1kV ranges both return erratic results. The output voltage is very low, e.g. 15v on the 500v range and 17v on the 1kV range. The oscillator for the high voltage generator is a TL494 WM chip with two outputs that have been paralleled and fed into the HV transformer via a 100Ω resistor. The IC is producing an oscillator output of about 6kHz form the IC. I checked the oscillator transistor which also seems fine. The TX primary and secondary both have continuity and both are ground (batt -) referenced on one side. On the secondary side there is around 256VAC which is then rectified. The output from the rectifier is a bit erratic, currently reading about 228VDC, but I have read over 500VDC there at times.

I am puzzled by the fact that although the output wire is quite thick and well insulated, the return is very thin and has very tight gaps to other parts. It feeds directly into at least 1 IC and has very tight gaps between it and some other parts. It does not seem to be ground referenced either. I am at a point where a circuit diagram would definitely be very helpful if anyone has one.

Since the low ohms range is working OK, it seems that metering is OK so the fault may not be anything too serious, but without a diagram I am struggling to make sense of this circuit.

thermionic · 21st Jan 2020, 7:58 am

Hi . Can’t help with a circuit, but these were made by Kyoritsu for Robin.

Cheers. SimonT

WaveyDipole · 21st Jan 2020, 3:43 pm

Thank you. That might be helpful. I have contacted the company to ask whether they can provide some service information.

WaveyDipole · 21st Jan 2020, 5:13 pm

Unfortunately, Kyoritsu are one of those companies that don't provide service information as it is "for our use only".

"I regret to inform you that we cannot supply a diagram to end users as this is for our use only but If you wish to send your meter in for repair we offer our own repair service for Kyoritsu products.
Contact...."

Ah well, it was worth a try. I might persevere a bit longer but its probably not worth spending much more time on so sadly this will probably end up in the bin minus a few parts!

McMurdo · 21st Jan 2020, 5:23 pm

not sure if I'm thinking about the right model but one of these we used to see suffered from insulation breakdown in the HV transformer, this would make the transistor run hot after being continuously operated and the arcing could be picked up on a nearby radio.

edit: just found an old note (dated 1991!), yes, it was a common problem for us on the 3001

WaveyDipole · 21st Jan 2020, 6:45 pm

It was working when last used but when I tried to use it recently it gave nonsensical, mostly over-range readings on the 500V and 1kV ranges for known resistor values. I tried it near a MW/LW radio. It generates some rather weird noises but no obvious loud cracking noise as might be expected from arcing on the HV ranges, except on the low ohms setting when it is quite noisy. The transistor gets mildly warm after prolonged testing but nothing out of the ordinary.

Thank you for looking up your notes and confirming the HV transformer problem though. The windings do not look like they have been sealed in any way so the beginnings of insulation breakdown certainly sounds like a possible explanation. It had been sat in my shed for some time so damp ingress might have been a possible factor, but it has now had a few weeks in the warm indoors to dry out.

20th Jan 2020, 2:57 pm	#1
WaveyDipole Nonode Join Date: Mar 2013 Location: Leicester, UK Posts: 2,535	Robin model 3001 I posted a request on EEVblog but had no luck so I guess this is a long shot. Does anyone have a circuit diagram for a Robin 3001 insulation tester or similar model or know where I can get one please? The low ohms function seems to work fine but the 500V and 1kV ranges both return erratic results. The output voltage is very low, e.g. 15v on the 500v range and 17v on the 1kV range. The oscillator for the high voltage generator is a TL494 WM chip with two outputs that have been paralleled and fed into the HV transformer via a 100Ω resistor. The IC is producing an oscillator output of about 6kHz form the IC. I checked the oscillator transistor which also seems fine. The TX primary and secondary both have continuity and both are ground (batt -) referenced on one side. On the secondary side there is around 256VAC which is then rectified. The output from the rectifier is a bit erratic, currently reading about 228VDC, but I have read over 500VDC there at times. I am puzzled by the fact that although the output wire is quite thick and well insulated, the return is very thin and has very tight gaps to other parts. It feeds directly into at least 1 IC and has very tight gaps between it and some other parts. It does not seem to be ground referenced either. I am at a point where a circuit diagram would definitely be very helpful if anyone has one. Since the low ohms range is working OK, it seems that metering is OK so the fault may not be anything too serious, but without a diagram I am struggling to make sense of this circuit. Last edited by WaveyDipole; 20th Jan 2020 at 3:19 pm.

21st Jan 2020, 7:58 am	#2
thermionic Heptode Join Date: Apr 2003 Location: Cornwall, UK. Posts: 989	Re: Robin model 3001 Hi . Can’t help with a circuit, but these were made by Kyoritsu for Robin. Cheers. SimonT __________________ The honesty of imperfection..........

21st Jan 2020, 3:43 pm	#3
WaveyDipole Nonode Join Date: Mar 2013 Location: Leicester, UK Posts: 2,535	Re: Robin model 3001 Thank you. That might be helpful. I have contacted the company to ask whether they can provide some service information.

21st Jan 2020, 5:13 pm	#4
WaveyDipole Nonode Join Date: Mar 2013 Location: Leicester, UK Posts: 2,535	Re: Robin model 3001 Unfortunately, Kyoritsu are one of those companies that don't provide service information as it is "for our use only". "I regret to inform you that we cannot supply a diagram to end users as this is for our use only but If you wish to send your meter in for repair we offer our own repair service for Kyoritsu products. Contact...." Ah well, it was worth a try. I might persevere a bit longer but its probably not worth spending much more time on so sadly this will probably end up in the bin minus a few parts!

21st Jan 2020, 5:23 pm	#5
McMurdo Dekatron Join Date: Jun 2009 Location: Staffordshire Moorlands, UK. Posts: 5,274	Re: Robin model 3001 not sure if I'm thinking about the right model but one of these we used to see suffered from insulation breakdown in the HV transformer, this would make the transistor run hot after being continuously operated and the arcing could be picked up on a nearby radio. edit: just found an old note (dated 1991!), yes, it was a common problem for us on the 3001 __________________ Kevin Last edited by McMurdo; 21st Jan 2020 at 5:27 pm. Reason: found my old note

21st Jan 2020, 6:45 pm	#6
WaveyDipole Nonode Join Date: Mar 2013 Location: Leicester, UK Posts: 2,535	Re: Robin model 3001 It was working when last used but when I tried to use it recently it gave nonsensical, mostly over-range readings on the 500V and 1kV ranges for known resistor values. I tried it near a MW/LW radio. It generates some rather weird noises but no obvious loud cracking noise as might be expected from arcing on the HV ranges, except on the low ohms setting when it is quite noisy. The transistor gets mildly warm after prolonged testing but nothing out of the ordinary. Thank you for looking up your notes and confirming the HV transformer problem though. The windings do not look like they have been sealed in any way so the beginnings of insulation breakdown certainly sounds like a possible explanation. It had been sat in my shed for some time so damp ingress might have been a possible factor, but it has now had a few weeks in the warm indoors to dry out.