Ampro 16mm Stylist projector woes.

[paddy ryan]

Hi folks-back again,
With reference to this amplifier problem, I have been away for a while, but would be very grateful if I could continue with the fault problem.
Les Jones and rjenkinsgb in particular, may I continue to pump your brains on this. Any other input would be appreciated as well gents!
I have done an insulation test on pin 12 to chassis ground (pin 7), at 500 volts, and get a reading of 0.06 ohms, having followed your suggestions.
The fuse still blows with the rectifier valve out.
As far as I can make out, the connector that mates with the P2 is connected to the auto transformer
So, If it is a ground fault on the transformer, how do I proceed now? Would this transformer need rewinding?
This projector is of the 1940s and looks a nightmare to get into, even taking the amp out is a major strip job just to get at it!
Last stop solution would be to get it fixed by an expert, but the cost would be prohibitive against what the projector is worth!

 

[Les Jones]

Can you take some pictures showing the incoming mains cable to where it connects to the auto transformer, the auto transformer and the cable between the auto transformer and the connector that plugs into P2. Also what is the mains voltage in your country ?

Les.

 

[Nigel Goodwin]

Hi folks-back again,
With reference to this amplifier problem, I have been away for a while, but would be very grateful if I could continue with the fault problem.
Les Jones and rjenkinsgb in particular, may I continue to pump your brains on this. Any other input would be appreciated as well gents!
I have done an insulation test on pin 12 to chassis ground (pin 7), at 500 volts, and get a reading of 0.06 ohms, having followed your suggestions.
The fuse still blows with the rectifier valve out.
As far as I can make out, the connector that mates with the P2 is connected to the auto transformer
So, If it is a ground fault on the transformer, how do I proceed now? Would this transformer need rewinding?
This projector is of the 1940s and looks a nightmare to get into, even taking the amp out is a major strip job just to get at it!
Last stop solution would be to get it fixed by an expert, but the cost would be prohibitive against what the projector is worth!

If it reads 0.06 ohms you didn't need a 500V insulation test, a simple multimeter on ohms (or even a light bulb and battery) should have easily done the job.

For a crude and nasty test you could try running it through an isolation transformer, assuming it's a short from primary to the core, then it should probably work fine then. However, it's also possible that as well as the short to core, there's shorted turns in the primary - in which case it would probably still work, but overheat fairly quickly. But at least with a test such as this, you should be able to make sure everything else works.

 

[paddy ryan]

Will do photos tomorrow. I am in the UK, so 240 volt mains.
The projector is 112volts, and I normally run it through a step down transformer. How would I run it through a 240 volt ISO transformer? Thanks for the info gents. Appreciated as usual;

 

[Nigel Goodwin]

Will do photos tomorrow. I am in the UK, so 240 volt mains.
The projector is 112volts, and I normally run it through a step down transformer. How would I run it through a 240 volt ISO transformer? Thanks for the info gents. Appreciated as usual;

If you've got a 240/240 isolation transformer, you go use that to feed your 240/120V auto-transformer. Or, if you've got a 240V/120V isolation transformer you could use that to replace the auto-transformer.

However, as you're in the UK, you've probably seen countless large yellow isolation transformers used by builders etc. to run 110/120V power tools from 240V mains, AND to provide safety isolation. If you get hold of one of those, that would drive the projector directly, and provide isolation.

 

[Les Jones]

Hi Nigel,
Although these yellow transformers provide isolation I think the center tap of the secondary is earthed so this would mean that there would still be a short between 55 volts and earth. (Or if the earth to the projector was disconnected you would get a 55 volt shock when touching the case.)

Les.

 

[JimB]

Although these yellow transformers provide isolation I think the center tap of the secondary is earthed

Yes it is in most cases that I have seen.

JimB

 

[Nigel Goodwin]

Well damn!

Although that easily be cured just for a test.

 

[paddy ryan]

Thanks gentlemen, I have an isolation transformer and have attempted to run the projector as advised. It started fine, but as soon as I turned on the amp it just conked out completely. the fuse is fine. I reckon it may be something to do with the switches, but have decide to abort! Taking this machine apart to even get at the back of the amplifier and the control switches means stripping down the whole machine, so I am going to cut my losses and have a go at something less challenging next time. I would like to say thank you to all you guys for the help, and I have actually learnt a lot as I have plodded onwards. As Mcarthy said "I will be back"!