Component Tester Fault

[Noidzoid]

One other thing, I'm not sure that schematic you have is correct, the only one I could find for the 605 disagrees with yours, but makes more sense.

I think there must have been a revision of something but there are differences.
The tracks match up with the schematic I have taken from this book.







As it was when first I saw it....

[AVGresponding]

Hmm well ok, but the legend on your layout indicates 2 mixed colour pairs, each red/brown, which is a recipe for confusion.
Since they seem to be for the +/- 12VDC rails, if they are implementing a centre tap by joining two secondaries, you better be 100% sure about the phase, or you're just making an impromptu space-heater...

[Noidzoid]

As inexperienced as I am, the last picture (of the wires in place as I found them) of the three in my last post makes more sense to me as each bridge rectifier has two wires each of the same colour going to ~pins. However, I can't be sure that the right pairs are going to the correct rectifier. Yours looks very different.
I wish mine was laid out like yours, it looks much tidier.

[Noidzoid]

@ThickPhilM

Just a thought, do you also have a different schem for the Z board? If so, does yours show 4 wires coming from the transformer like my scope or 3 like my schem?

[StillTrying]

I think I've got the same pdf as ThickPhilM,  hameg_hm605_oscilloscope..........pdf  the Z board seems to have 3 power wires.



If the tube heater current is flowing though those vi and ye tracks perhaps they're used as a fuse.

[Noidzoid]

I think I've got the same pdf as ThickPhilM,  hameg_hm605_oscilloscope..........pdf  the Z board seems to have 3 power wires.

(Attachment Link)

If the tube heater current is flowing though those vi and ye tracks perhaps they're used as a fuse.

Well, at the moment I am lost. You would think an official manual (assuming it is of course) would put wire colours in? Why is there such a difference between our schematics?  How did whoever put in this transformer know which wires to put where without info from the schematic? (Unless of course like for like was done). If there isn't a different schematic out there what is the transformer and board I have?


Also the board I have does seem to correspond to the schematic including the extra hole where the shared track is with two small posts with a purple on one and violet on the other.

The Y board schematic I have although unlike ThickPhilM's one, does seem to have the same track pattern. Is it possible I have an early model and manual before they tidied both up a bit?  The wires on mine look like afterthoughts that were drawn in just before being sent to the printers.

[Noidzoid]

Only three wires from this part of the transformer going to the Z board?

The only place I am seeing the fourth wire is in the scope itself!

[StillTrying]

I don't think the 6.3VAC and 31VAC windings are a very big problem. I can imagine it being shown on the schematic as just one 0-6-37 winding, but when they come to build the actual transformer it's made from a high current 6.3VAC winding and a low current 31VAC, at least they used the similar blue and violet colours for the center point.

After correcting the misplaced rd wire on the drawn version, the three images in Reply#50 all look the same to me, the bn looks very or in the photo, and the soldering's terrible.

I still think ThickPhilM's 1.1R and 201R for those windings seem high, the 240VAC primary winding might be only ~200R.

Disconnect all the secondaries.

[Noidzoid]

I still think ThickPhilM's 1.1R and 201R for those windings seem high, the 240VAC primary winding might be only ~200R.

Disconnect all the secondaries.

In regard to disconnecting the secondaries with reference to post #32 the measurements were taken with all the secondaries disconnected (well one from each coloured pair) but with the Z board four still connected at all times.  Should I have disconnected those too? Will that be not giving me correct results? Should I disconnect the Z four and measure them all again?

Also could I trouble you for a concise step by step instruction on how to test the Z board four once I have unsoldered them.  I have been reluctant to mess with them so far as I understand this area should be treated with great caution. (I thought I needed a HV probe? Or would that be further into the Z circuit?) I am just trying to be respectful with regard to what I am unsure of.

[StillTrying]

In regard to disconnecting the secondaries with reference to post #32 the measurements were taken with all the secondaries disconnected (well one from each coloured pair)

I've assumed you disconnected each secondary one by one, reconnecting the last one before disconnecting the next, which would be different than with all the secondaries disconnected. But still that should have been good enough to find which supply was pulling the rest down.
The amount of power to pull all the secondaries down to only 60% should be more power than the whole scope uses, something should be getting very hot in theory.

"Should I have disconnected those too? Will that be not giving me correct results? Should I disconnect the Z four and measure them all again?"

Looking at the schem. I think it would be safe (for the scope!) to disconnect the 0V AND 37V ends of the 0-6-37 winding (rd and ye), but if the other supplies are still connected these disconnected rd and ye ends would still be at -1200V because of the still connected vi and bl.

"Also could I trouble you for a concise step by step instruction on how to test the Z board four once I have unsoldered them."

You could disconnect the 0-6-37 's mid vi and bl as well, then you'd just have a 6.3VAC winding and a 31VAC winding that are isolated and not at -1200V, but the solder tags the 0-6-97 were disconnected from would still be at -1200V.
I'd be happy to measure these 6.3VAC and 31VAC at -1200V, but I'd connect the DVM before switching on and not touch my toolbox DVM while it was at -1200V.

I still think the best, safest and easiest idea is to have all the secondaries disconnected to see what the transformer does fully unloaded, and there'd be no HV then other than the mains.

Also resistance of Primary Winding 40.2ohms

A ThickPhilM's resistance measurement of his primary might be useful.

[AVGresponding]

The primary on mine measures 55.4 ohms, disregarding the last 2 digits (didn't warm the meter up).

Bear in mind mine is a 203-6, with a manufacture date of 52/87.

The layout I posted an excerpt from is the only one I could find for the 605, and all the text is in German. All the English manuals I could find were user only, not service. I suspect it might be a later version than yours.

[Noidzoid]

Been doing some measuring with a different meter (TTi 1705) as I think my other one was being a bit odd.

Just thought I would share what I have with those of you that have been helping so far before removing the Y board (which will be easier before putting the transformer wires back) to gain better access to the larger electrolytic capacitor legs.

[StillTrying]

Those all disconnected readings show the transformer is fine.
It must be something else. 

[Noidzoid]

Found two capacitors that seem bad.
Can they become totally open circuit? They are not registering any change whatsoever on the ESR meter (MESR-100). Both these caps have the same values printed on them. 220μF 100v



The other three similar looking 1000μF 25v caps on the same board all tested good with the same meter.

[AVGresponding]

Given the low cost, I'd replace them anyway. Sometimes they only exhibit the failure mode with a higher voltage applied than a tester can supply.

Short or open circuits are both possible, with all points in between...

EDIT: Failure can also be intermittently apparent due to thermal variation.

[StillTrying]

Found two capacitors that seem bad.
Can they become totally open circuit? They are not registering any change whatsoever on the ESR meter (MESR-100).

Not often, but they can dry out and have very a low capacitance.

Almost no smoothing capacitance on the +68 and +140 supplies would be enough to explain the wiggly traces, and maybe some of the low voltages if their discrete regulators were struggling.

[Noidzoid]

Just connected a 'bad' one up to a DMM as I was curious to see if it was totally open (20MΩ range) and it seemed to settle on a reading of 5.7

So this is obviously just a straightforward resistance and not ESR. Does this throw any light on anything?

Also could I have some advice regarding buying new caps.
I have found several from RS and Farnell matching the μF, v, leg spacing and taking into account general cylinder dimensions.
Is there anything else I should be considering like °C, hrs ESR (this last one when stated seems to be quite variable).

I don't imagine any of the offerings from these outlets are 'rubish' and I don't need overkill as this is an old scope. I just want it to work properly.

[StillTrying]

Yes they don't have to be too special or low ESR, but I nearly always buy 105C.

I don't know why you can't get a proper ESR and capacitance measurement. It might be better to check a few others of the big electrolytics before ordering just 2 caps.
I often use these for a few bits, £1.90 postage is not too bad for <24Hr delivery.
https://www.bitsbox.co.uk/index.php?main_page=product_info&cPath=65_66_69&products_id=2511

[AVGresponding]

It's dead.

A good cap will show steadily climbing resistance until the resistance scale of the meter is exceeded, when using a normal meter.

Technically it'll never have infinite resistance since there'll be a leakage current, but in practice this is usually much smaller than the resistance measurement current that the meter will supply.

[Noidzoid]

OK thanks good people.  I've decided to replace all the aforementioned caps.

Next I thought I'd test the bridge rectifiers while they are easy to get at. I'm pretty confident about how to go about it but need to know if they can be tested in circuit or should they be removed for testing?

[AVGresponding]

It depends what else is in circuit. Often they can be tested in circuit, but occasionally other components can cause false readings.

As long as you're sure nothing else is affecting your reading, there's no reason to remove them.

[Noidzoid]

Within the small sphere of my understanding the bridge rectifiers are ok.

I've replaced the two 'bad" caps and the other three as it has been pointed out heat could make them unreliable intermittently.  I also followed the example above and bought the 105°C ones.  Thanks for the guidance.

Along the way I have learned two lessons.
When unsoldering one of the caps (with it hanging from the board pointing down), it fell out! It the dawned on me that I hadn't taken note of where the negative stripe was. So, first lesson was make notes and/or plenty of photos. Fortunately I managed to find one that just about showed the stripe on the wayward cap. (Pure luck!)

Very pleased with myself after having soldered all five caps in place, I turned the board over, only then did I notice that two of the new ones looked physically taller than the old ones, so much so I wasn't sure the case would fit! After putting a straight edge where the case would rest I was relieved to find it didn't touch, though I think the only way to measure the gap would be with a feeler gauge. I just hope when the scope is working, any heat doesn't move anything due to expansion.  So, second lesson for the idiot that should know better is physical size is just as important as other specifications when choosing components.

After you guys have picked yourselves up off the floor or just rolling your eyes, here are some pictures of my handywork so far so you can do it again........



I did cut the legs off

[Noidzoid]

Thank you, so very very much to all who have helped me get this far.  First tests are showing excellent results.

The component tester test is doing exactly what it should, which is the reason this whole project started.

Probes disconnected


Probes connected


All that is left is putting the cover back on and learning how to actually use an oscilloscope. 

Did I say Thanks?

Just to make sure, THANKS GUYS!

[AVGresponding]

Glad to see it up and running again.

Them lil' bastard caps cause soooo much trouble, not just in TE (have one/some failed in my TV, makes it lose settings, and lose ability to detect it has a signal so it triggers the 5-minute auto power off, too much hassle to chase it/them down)(at the moment xD)

[StillTrying]

I/we were close in Reply#14.   "We could imagine no decoupling on the Y's supply voltage, ...or something."

Where did you get the new caps from so quick, and how is it on other wave forms.

An old one..

as the secondaries are individual coils not shared therefore the only thing they have in common is their relationship with the primary?

As well as the primary the 1 magnetic field is common to all the windings, shorted turns anywhere would cause all the secondary voltages to be too low and the primary current to be too high.