Component Tester Fault

[Noidzoid]

When I first tested this feature out on the HM605  it appeared to work just fine.  I followed the instructions in the manual, pushing the CT button, connecting the tester socket to one of the earth sockets by BNC socket and watched the horizontal line go vertical.
Great I thought. As I had a few other things to do I left the scope turned on as I read in the manual that turning it on and off for short periods is not good for the CRT, but I turned the intensity right down so the trace was no longer visible.
On returning, I went to repeat the test as I thought it was quite neat to see.
Turned the intensity up to make the trace visible, pushed the CT button to be greeted with this image.....

Also noting the overscan lights had illuminated.
I released the switch, the messy image disappeared but the overscan lights stayed on.
I thought dirty switch? So pushed the button in and out a few times and the lights went out.
Pushing the button in again this time connecting the leads as I had before I see this mess.

I can understand the overscan lights being illuminated in this instance.
I can't think of anything I did different other from turning the intensity down for a few hours. Is this an open it up project or am I missing something obvious?

[Noidzoid]

This is what happens when I fed the scope 50kHz, auto triggering, 5v p-p, channel 1 and 2 tested individually, both set to AC.





As can be seen no matter where the trace is put vertically the irregular fainter lines seem to emanate from the straight line that never leaves its position half way up the screen.

[Noidzoid]

Measurements on the graticule seem to be correct for the main and brightest part of the image. 20kHz 10v

[Noidzoid]

I can get rid of some of the rubbish by turning off auto triggering and tuning into this but I can't get it to settle.

[Noidzoid]

Following the instructions for probe adjustment this is what I get so I'm not blaming the source of the sine wave I gave it in the previous posts.

[Noidzoid]

Removing probe from test socket but still connected to BNC shows this.....

Trigger light on and lower overscan light on

[Noidzoid]

As I went to remove the probe I noticed the movement on the screen. On moving the probe around this is what happens...

 I wondered if it was the probe but both probes that I have behave the same

[StillTrying]

It looks just like (or mostly) an intermittent connection in the probe or 1kHz socket to me, or somewhere else.
I wouldn't worry about the 50kHz of open circuit noise.
Having the trigger on DC coupled is probably better.

[Noidzoid]

From the other source no probes attached

[Noidzoid]

It looks just like (or mostly) an intermittent connection in the probe or 1kHz socket to me, or somewhere else.
I wouldn't worry about the 50kHz of open circuit noise.
Having the trigger on DC coupled is probably better.

I don't think it is either of the probes as both of them behave the same.  Also when I unplug them completely the problem is still there as in the following image....


As this only started after leaving it on with intensity turned right down is there any possibility of a link?

Also if nothing is connected to the scope should it be triggering at all?

[bob91343]

My guess is that you need to repair this unit.  First check the power supply; this could easily be caused by bad filter capacitors or other faults.  Get the service manual and verify integrity of the power rails.
 
If that is good, I might think you have a bad CRT.

[StillTrying]

Is the component tester off.
Are you sure it's in single channel mode, ALT and CHOP can cause similar effects.

[Noidzoid]

Is the component tester off.
Are you sure it's in single channel mode, ALT and CHOP can cause similar effects.

Component tester is in the off position. When it's on the first picture in the first post of this thread is still what can be seen. In single channel mode, ALT and CHOP button out.

[shakalnokturn]

Definitely check power first. (Always check power first...)
If power hasn't failed, ideally you'd need another scope to follow a sine from input through to Y plates.

[StillTrying]

After that many tests it's not looking good, it looks like the Y amplitude keeps dropping back to the 0V position.
We could imagine no decoupling on the Y's supply voltage, ...or something.

Is CH 2 the same.

[Noidzoid]

After that many tests it's not looking good, it looks like the Y amplitude keeps dropping back to the 0V position.
We could imagine no decoupling on the Y's supply voltage, ...or something.

Is CH 2 the same.

Yes, both channels same

[Noidzoid]

Unless I am going about this all wrong I think there may be a fault with the power supply.
None of the secondary coils (I'm assuming it has multiple) are measuring anywhere near what they should, (if I am taking the measurements correctly of course).

Here is what I'm looking at......
This


I assume relates to this


Taking these into account and the reading up I have been doing on primaries and secondaries, with the scope turned on I measured the V~ across each pair of same coloured wires (assuming rightly or wrongly this indicates they are all individual secondary coils in their own right).

These are the results.

Should be
bk - 12v~
gr - 8v~
bn - 15v~
rd - 15v~
gn - 70v~
bl - 68v~

Actual
bk - 7.1v~
gr - 4.9v~
bn - 8.8v~
rd - 8.7v~
gn - 40v~
bl - 42.5v~

[Noidzoid]

Also I found one of the black wires was not secured to the little post sticking up on the board so I re-soldered it back.

I have made no tests regarding the CRT or the Z board.

[SeanB]

Unsolder one end of each of the secondary wires and measure again. if they rise up to about correct then one of the bridge rectifiers is shorted, a capacitor is shorted or something after the bridges. If not the transformer is terminal, with shorted windings internally.

If not the transformer connect secondaries back one by one to find which one is loading the rails down, and that at least gives you a start.

My bets are on green, probably failed bridge rectifier, and if you change one of those little ones change the whole lot as a single operation, as they are all the same batch, and the 8V rail probably has the highest current in operation, and thus failed first from cooking. Use higher current rated devices, at least 2A over the 1A ones, though you will probably have to space them a little off the board and use sleeving to get the leads to fit the spacing, but they will run cooler.

Had plenty of expensive failures from bridge rectifier faults, so got used ot running a scope probe over each power rail to see ripple before any other test, to see if there were any open or shorts, which would not cause an immediate fault, but would lead to transformer failure eventually.

[StillTrying]

I can't imagine it working as well as it does if all the voltages were only 60% of what they should be, are you sure the DVM is accurate. None of those transformer connections look original to me.
Beware the lethal voltages, do everything one handed, and don't get into the habit resting any fingers on the chassis, or anything else.

Yes start with gn, then bl, perhaps.

[bob91343]

The fact that all the voltages are roughly half of what they should be makes me think you have the primary set to the incorrect power line voltage.

[shakalnokturn]

The fact that all the voltages are roughly half of what they should be makes me think you have the primary set to the incorrect power line voltage.

OP mentions that fault happened while turned on, was working normally on powering up. Usually line voltage selectors don't flip themselves.

As suggested checking amount of AC on the DC side of the bridges could give you a clue to a defective bridge or overload on one power rail.

With all those voltages measured so low, is CRT brightness lower than it was before the fault?

Usually a secondary overload would cause significant heat somewhere, in this case probably enough for it to actually smell odd.

A partial internal short on the transformer will usually give a very hot transformer, or noise if arcing on the HV winding.

You may want to check over excessive resistance between plug and transformer primary, that could cause low secondaries without showing too much heat.

[Noidzoid]

With all those voltages measured so low, is CRT brightness lower than it was before the fault?

I'd have to say no, I don't think so.
Since first using this scope I have never turned the intensity right up. It is VERY bright to the point where it is more like a torch. So to be kind to the screen I always keep intensity low, it mentions this in the manual.

When leaving it for a few hours I even turned it all the way down, thinking I was being kind to it. On returning is when I noticed the above goings on.

There does appear to be four more secondaries coming from the transformer to the Z board behind the CRT, but they are not colour coded pairs like the others.  I haven't touched anything on this board at all (apart from moving it carefully to gain access to a screw when checking main power input (which is as you have already pointed out is on the correct input setting)).

[StillTrying]

"There does appear to be four more secondaries coming from the transformer to the Z board behind the CRT, but they are not colour coded pairs like the others."

There's another 3 wire winding supplying 6.3V and 30V to the CRT, but beware this winding and these voltages are at -1250V!

The rd and bn 15VAC windings provide + and - 12V supplies, both with 7812s, your measurements of 8.8 and 8.7VAC wouldn't be enough for the 7812s to regulate, which is probably enough to explain the wobbly traces.

But I don't know what's wrong with it! The schems in this German manual aren't very clear.

[Noidzoid]

There's another 3 wire winding supplying 6.3V and 30V to the CRT, but beware this winding and these voltages are at -1250V!

I did notice something along those lines when I saw this, and thought caution