Dynatron Henley RG33W radiogram

[Vintage84]

Originally Posted by Vintage84

The wire between tag 4 and 1 might be broken.

It is definitely broken.

[julie_m]

OK, I'm confused now. It looks to me as though mains live goes to the left-hand side of the fuse, the right-hand side of the fuse goes to the voltage selector, and then red, orange and yellow wires from the voltage selector disappear straight down into the windings. The red and orange wires don't seem to connect with tag 1. Can you confirm or deny this, please? Also, can you get a photo of the other side of the voltage selector?

EDIT: Never mind, I can see from the pictures you posted while I was typing.

With the set powered off, try your meter on an ohms range across tags 4 and 5. If you see a low resistance, then temporarily disconnect one meter probe, change the meter to AC volts, reconnect the probe and apply power. Note the voltage reading.

[Station X]

I agree Julie.

There appear to be four wires on tag 1.

One goes into the winding.
One goes to tag 7. (Centre tap of HT winding).
One goes to tag 4, or would do if it wasn't broken.

Where does the fourth wire go to? I'm guessing it connects to chassis.

[ms660]

Magnify the 2nd picture in post #79, look at the link wire, do you see what I see (fused or un fused as it were?)

EDIT: ....The blob.

Lawrence

[Station X]

The OP says it's definitely broken.

We have:-

Red, Yellow and Orange wires connecting mains live to the voltage taps on the mains transformer primary.

Tag 1?? (probably grounded as there's no wire from tag 4 or 7 to ground, but which winding is it connected to)?
Tag 2 mains neutral.
Tag 3 not used.
Tag 4 ??
Tag 5 one end of heater winding.
Tag 6 one end of HT winding.
Tag 7 centre tap of HT winding.
Tag 8 other end of HT winding.

[peter_sol]

If the wire from pin 1 to pin 4 is broken, remove the remains and solder a new piece of wire in its place.

[ms660]

Hard to say for me from the pics so far but I would guess that Tag 1 might be connected to an internal screen, Tags 4 & 5 being connected to the heater winding.

I wonder if that O/C bare wire link is standard wire or fusible stuff?

Lawrence.

[julie_m]

There is a dim scenario building in my mind, as follows.

If there was a short circuit on the heater connections, this would draw too much current from the transformer. Energy doesn't come from nowhere, so there would also have to have been too much current flowing in the primary. Chances are, the first time this happened, the primary fuse blew, but that wire between tags 1 and 4 was weakened. When the primary fuse was replaced and the set powered up with the short-circuit still in place, the wire between tags 1 and 4 melted through before the fuse did.

Now we know the short-circuit isn't there now, because we got a very high resistance reading with no valves (and the 5.1 ohms of the magic eye heater isn't cause for concern). So, has one of the valves perhaps somehow developed a dead short across pins 4 and 5?

While the valves are still out, test on an ohms range across pins 4 and 5 of each valve in turn. If one of them is an ECC83, test also between pins 4 and 9 and pins 5 and 9. (Count clockwise from the gap, as you hold the valve with the pins facing towards yourself.)

[Vintage84]

Originally Posted by julie_m

With the set powered off, try your meter on an ohms range across tags 4 and 5. If you see a low resistance, then temporarily disconnect one meter probe, change the meter to AC volts, reconnect the probe and apply power. Note the voltage reading.

1.5ohms
7.4v

[ms660]

Yes, it could be at the critical stage now, transformer obviously been stressed once, another stress might allow sod's law to kick in.

It would also be worth doing a full visual check on the heater wiring and pins 4 & 5 of the valve sockets for any.....could have/might have/it will do....shorts.

Not forgetting any scale bulb holders, wouldn't be the first time I've seen those causing the demise of a mains transformer.

Lawrence.

[Station X]

Originally Posted by julie_m

There is a dim scenario building in my mind, as follows.

That scenario would fit the facts, so long as one side of each valve's heater is connected to chassis. Then if tag 4 were disconnected from tag 1 (which it is) there'd be no heater voltage.

A voltage reading between tags 4 and 5 would confirm this diagnosis. Previous readings have been taken between tags 5 and 7 on the basis that tags 4 and 7 was earthed, but they aren't due to the broken link from tag 1 to tag 4.

[Station X]

Originally Posted by Vintage84

1.5ohms
7.4v

That's good, but it differs from the results in post #72. Have you reinstated the link from tag 1 to 4?

[peter_sol]

OK you now have 7.4v heater voltage with no valves in
Why not fit each valve back in on its own and see if the heaters light. leave the rectifier till last

[ms660]

I'd do a visual shorts candidate check first.

Lawrence.

[Station X]

I see I have confused tags 4 and 5 on the transformer with tags (pins) 4 and 5 on the valveholders.

If the 7.4V is present at the transformer, but not on the valveholders, there's a break in the wiring somewhere. Possibly the link between transformer tags 1 and 4.

[Vintage84]

Originally Posted by julie_m

While the valves are still out, test on an ohms range across pins 4 and 5 of each valve in turn. If one of them is an ECC83, test also between pins 4 and 9 and pins 5 and 9. (Count clockwise from the gap, as you hold the valve with the pins facing towards yourself.)

Pins 4&5:
ECC85: 3.5
4x ECL82: all between 2.3 and 2.6
EBF89: 4.1
EZ81: 4.1
Unknown valve: 4.1
ECC83: 14.7

Pins 4&9:
ECC83: 8

Pins 5&9:
ECC83: 8

[Station X]

No obvious short circuited heaters.

Has the tag 1 to 4 link been replaced?

Are you now getting 7.4V on tags 4 and 5 of the VALVEHOLDERS?

[Vintage84]

I haven't replaced this yet. What type of wire should I be using?

With no link between tags 1 and 4, the voltage between pins 4 & 5 on the valveholder is 0.56.

[Station X]

The last thing I want you to do is damage the transformer.

Confirm that you still have 1400 kohms between pins tags 4 and 5 of the valveholders.

You should also see 1400 kohms between tags 1 and 5 of the transformer.

If so fit an insulated wire link between transformer tags 1 and 4. Then confirm that you see 1.5 ohms between tags 4 and 5 of the valveholders.

If so apply power and confirm that you have 7.4V between tags 4 and 5 of the valveholders.

If so refit the valves and confirm they light up.

[julie_m]

If you just solder in one single strand from a piece of stranded connecting wire, that will act as a crude fuse. If the short-circuit is still present, the thin wire will melt through and disconnect the current, protecting the transformer.

If a single strand survives the application of power, that means the short circuit has been cleared. You will need to replace it with something stronger, though, before you put the valves back!

Do Graham's suggested tests first, though.