Dynatron Henley RG33W radiogram

[Vintage84]

I don't have any insulated wire to hand, so I've done a temporary fix for now.

Reading from tag 1&5: 1.1ohms. Same reading on pins 4&5 on valveholders

[Station X]

We need to be sure that the 1.1 ohms is the resistance of the heater winding and not something connected to tag 1 of the transformer. Did you measure 1400 kohms from tags 1 to 5 before you made the link?

[Vintage84]

Originally Posted by Station X

We need to be sure that the 1.1 ohms is the resistance of the heater winding and not something connected to tag 1 of the transformer. Did you measure 1400 kohms from tags 1 to 5 before you made the link?

I've just broken the link and have 2ohms between tags 1&5, not 1400kohms

[Station X]

I'm trying to get my head round this.

You have 7.4 VAC on tags 4 and 5 of the transformer, but not on tags 4 and 5 of the valveholders. You're going to have to trace to wires from tags 4 and 5 of the valveholders back to the transformer and see which tags they connect to.

[Vintage84]

Tags 1 and 5 of the transformer do link back to pins 4 & 5 on the valveholders. I haven't checked whether I have 7.4v on the valveholders since repairing wire between tags 1 and 4 though.

[Station X]

If you measure 1400kohms at the valveholders pins 4 and 5, you should measure the same on tags 1 and 5 at the transformer. With the link out that is.

[julie_m]

Originally Posted by Vintage84

I've just broken the link and have 2ohms between tags 1&5, not 1400kohms

Assuming no valves are fitted, that can only be your short-circuit rearing its ugly head again. Leave the meter connected to tags 1 and 5 and inspect the heater wiring carefully, looking for any damaged insulation (especially on the brown wire, which is the non-earthed side of the winding) or valveholder contacts touching one another. A small, bright LED flashlight and a magnifying glass will help. Do the wires pass through any holes in metal? A stray sharp edge could have worn away at the insulation. See if you can cause the resistance to increase by gently manipulating the wires.

When you find whatever it is that has been touching something it shouldn't, then it should be possible to introduce some insulation to prevent it from happening again.

[ms660]

What we know...The mains transformer appears to have suffered some stress, the wire link between tags 1 & 4 on the transformer had blown.

Something caused excess current draw, the heater circuit would be the first suspect.

So...With a wire link in place between tags 1 & 4, disconnect the brown wire from tag 5, connect meter between tags 1 & 5 apply power and measure the AC voltage, should be at least 6.5 volts AC, if so then leave running for a while and keep an eye on things.

If all's ok then switch off power and with no valves or scale/pilot bulbs fitted do a resistance check between the disconnected end of the brown wire and Tag 1 of the transformer, if a reading much less than infinity is shown then that should be investigated, if infinity then leave meter connected and have a good visual check and prod around the usual suspects (keeping an eye on the meter display) such as valve socket tags/bulb holders etc etc that show a possibility of shorting out, check out for blobs of solder rattling around.

If all's ok then reconnect the brown wire, refit some of the valves (not the rectifier) and check if they light up, if they do then fit the other valves (not the rectifier) and let it run again, if all's ok then fit the rectifier valve and see what happens...You could use a lamp limiter or just rely on the quick finger on the power switch technique.

A lot of this has already been covered...Just consolidating.

Lawrence.

[Vintage84]

Thanks again for all the help and advice!

I will be really busy at work for the next couple of days, so might not be able to trace the short circuit until later in the week.

I'll keep you posted with what I can find.

[Vintage84]

With the link broken between tags 1 & 4 on the transformer and valves all removed, I have 2.2ohms between pins 4 & 5 on the valveholders and 2.5 between tags 1 and 5 on the transformer.
It is only with the link between tags 1 & 4 that I have 1400kohms on the valveholders.

[peter_sol]

I Think someone local needs to help you as we are getting nowhere with 110 posts already.

[Nickthedentist]

I'm thinking the same. You're obviously keen to have this lovely machine working and you have proved that you basically know how to use a meter, but as has been hinted at before, you may only have one more chance before the mains transformer gives up the ghost entirely and the unit suddenly becomes uneconomical to fix.

It could well be that somebody could show you what to do fairly quickly face-to-face, whereas over the internet, it could take us forever.

Good luck,

Nick.

[Station X]

Originally Posted by Vintage84

With the link broken between tags 1 & 4 on the transformer and valves all removed, I have 2.2ohms between pins 4 & 5 on the valveholders and 2.5 between tags 1 and 5 on the transformer.
It is only with the link between tags 1 & 4 that I have 1400kohms on the valveholders.

This just cannot be true. Inserting a link in a powered down circuit. can only lower the resistance between two points, not increase it.

Your post also conflicts with information given in post #72 which gives results with the link broken.

Are you sure about your readings?

As suggested I think you need to seek assistance with this, if you're to avoid destroying the mains transformer.

[Vintage84]

I'll retest all my readings as I'm also finding the results confusing, but have always taken them a couple of times before posting to ensure accuracy.

Open to offers of local help... I'm in East London (E11).

[peter_sol]

Where in E11?

[peter_sol]

Lets try this.
look on the valve holders and decide which of the pins (4 or 5) (not the ECC83) goes to the chassis.
The other pin will go to all other valves.
Trace that wire back to the mains transformer and noting where it is connected, unsolder it.
Then check the resistance from that wire to the chassis with ALL the valves out including the magic eye..
It should read infinity in other words no connection.
If there is a reading, then there is a short somewhere which you need to trace.
We have said all this before but it seems to have got lost.

[Michael Maurice]

Originally Posted by peter_sol

Where in E11?

E11 is Leytonstone, i've got to go to Wanstead possibly next week if thats any help.

I've got all the service manuals on my laptop.

[Vintage84]

Hi Peter.
I'm in Wanstead.
I haven't had chance to follow those instructions yet (hopefully I will be able to do it after work tonight).
Thanks again,

[ms660]

First off.....Don't give up yet....Doing remote diagnostics via forums can sometimes be difficult due to miss interpretation of what's what between the OP and other forum members and visa versa, it happens all the time.

You could try the suggestion in post #108, pay attention to any scale bulbs/lights etc, if fitted they need to be removed for the tests.

Report the measurements/outcome etc.

Good luck.

Lawrence.

[julie_m]

Post 110 suggests to me that there is an intermittent short-circuit somewhere in the heater wiring, which is making and breaking contact as things are moved around. Remaking the link from 1 to 4 could be a red herring.

I think it will need a careful examination. Maybe even a fresh pair of eyes.