Hameg 408-1A

[Specmaster]

I have just aquired a pair of scopes, one is a Philips PM3217 and the other is the Hameg 408-1A. Both have some issues and I need a manual, user and service for the Hameg in order to get on with trying to resolve the issues it has, the Philips I have downloaded manuals for.

I have searched high and low on the internet and the only manual I can find for the Hameg is one in German. Can anyone loan me copies or tell me where to look for them on line at all? 

[tronde]

Hameg gives you the English user manual for HM408 and the service manual for HM408-1A in German, but with English text in the schematics part.

https://www.rohde-schwarz.com/search/hameg-archive_229476.html?term=hm408

I don't know what the diiference between 408 and 408-1A is, but you can compare the schematics if you download the German manal for 408. You can send them an email and ask if they have a service manual in English. They will most likely send you one if it exist.

[Specmaster]

Thanks for the link, both English and German manuals downloaded, English is 408 and Geman is 408-1A. Interestingly, they both appear to be the same as far the control panel is laid out so perhaps the 1A is just a later modification to the circuit?

It is a pig to work on, I have struggled to remove the board containing the timebase controls as neither of the vernier controls where functioning so it was impossible to set them in the "CAL" setting. Reason for the failure was the nylon flexible shaft couplers have split in half possibly as a result of being over tightened or rough handling? This it seems has been a common failure on this particular scope.  All I know is that I find myself needing to replace all of them, 11 in total, anyone have any ideas where these could be sourced from at all?

I have also noticed  that on the digital output board there is a capacitor that has either blown or been smashed (looks like its been chopped), schematic shows it as being  a 100pf 100v (grey with a black cap on top), cant recall seeing a capacitor that looked this before. Nothing came out of the case when dismantling it and there is no sign of any magic smoke having been released either?                                                                                                                                         

[tautech]

Pics please.
They don't need to be bigger than 100kB for us to see enough detail.

If the couplers end up being too hard to manufacturer ask Rich how to go about sourcing them in this thread:
https://www.eevblog.com/forum/testgear/rohde-schwarz-oscilloscopes-questionscomments-let-me-know!/

Hunt out the part # so it makes it easy for him.

[Specmaster]

Pics please.
They don't need to be bigger than 100kB for us to see enough detail.

If the couplers end up being too hard to manufacturer ask Rich how to go about sourcing them in this thread:
https://www.eevblog.com/forum/testgear/rohde-schwarz-oscilloscopes-questionscomments-let-me-know!/

Hunt out the part # so it makes it easy for him.

Pics are on their way, however after careful examination its only 5 of these particular couplers I now require as the others are metal and are OK. Someone has tried to fix some of these before me by wrapping wire around them and they still fail so a replacement is required.

I have no idea how I'm going to hunt out the part number since the Hameg manual unlike many others, does not have a parts list along with the relevant part number contained within the manual. Perhaps this is available from the makers direct?

[tautech]

I have no idea how I'm going to hunt out the part number since the Hameg manual unlike many others, does not have a parts list along with the relevant part number contained within the manual. Perhaps this is available from the makers direct?

That should not matter, just ask Rich in the thread I linked and provide a link back to this thread, he'll sort it out for you. Pics and location, maybe with a short description should give him the info or at least enough to link to one of their staff at the factory to hunt them out for you.

[Specmaster]

Here are some pics of the progress so far, pic c1b shows 2 caps in the power supply which look like that they have suffered a leak, still working though and pic c2b also shows another cap in the psu which has been sucked inwards? These I will be replacing as a precaution once I have figured out to remove this board to access the solder side.

Pics c3b and c4b show some of these couplers and how someone has tried before to cure the problem.

Pics c5b and c6b show the "blown" cap on the digital output board from the side and above views.

Any thoughts?

[tronde]

Maybe you can use something like this as replacement for the couplers? You get them in a lot of different dimensions for input and output shafts.


https://www.banggood.com/3mm-x-6_35mm-Aluminum-Flexible-Shaft-Coupling-OD19mm-x-L25mm-CNC-Stepper-Motor-Coupler-Connector-p-993317.html?rmmds=search

[theatrus]

The first caps def leaked. The dented cap may have come that way from the factory.

That sliced cap though - maybe its just a decoupling cap and no one ever noticed?

[Specmaster]

The first caps def leaked. The dented cap may have come that way from the factory.

That sliced cap though - maybe its just a decoupling cap and no one ever noticed?

The dented cap, could have come from the factory like that I suppose, but what would that have done to the capacitor rating? The scope looks as if it was made late 1990 or early 1991 and given its age and the possibility that this cap was compromised  at least because the dielectric insulation must be weakened by the dent, I'm surprised that it has not blown already?

As to the sliced cap, yes I think it is a decoupling cap as it sits across the output of an IC to ground, would a 10pf 100v ceramic disc capacitor suffice as a replacement or not? 

[Specmaster]

The flexible shaft couplers that I need are way smaller then those on offer from Banggood, the input shaft is 2mm and the output 4mm, length is 15mm and overall dia is just 12mm and these are in some cases sitting very close to the solder side of PCB's so I would not like to much larger in overall dia than that, the banggood ones are 25mm dia.

[carl_lab]

The flexible shaft couplers that I need are way smaller then those...

Maybe you can use a short piece of PVC air hose, if the potentiometer or switch is not too rough-running.

[coromonadalix]

yeah  +1  exactly my tought,  with the correct inside diameter,  it would do nicely while having a flexible functionality, there's some tubing who wont dry out in time ...

you could check some Radio Controlled websites they offer lots of parts ... 

[tronde]

You get them smaller than those from banggood, but maybe still too large.

Here is one that can sell you 2x4mm D15 L20.

https://www.aliexpress.com/item/1pcs-5mm-x-8mm-D15-L20-shaft-coupler-flexible-coupling-stepper-motor-encode-for-5mm-shaft/32670333088.html

You can also try with adhesive lined heatshrink tube.

[theatrus]

The first caps def leaked. The dented cap may have come that way from the factory.

That sliced cap though - maybe its just a decoupling cap and no one ever noticed?

The dented cap, could have come from the factory like that I suppose, but what would that have done to the capacitor rating? The scope looks as if it was made late 1990 or early 1991 and given its age and the possibility that this cap was compromised  at least because the dielectric insulation must be weakened by the dent, I'm surprised that it has not blown already?

As to the sliced cap, yes I think it is a decoupling cap as it sits across the output of an IC to ground, would a 10pf 100v ceramic disc capacitor suffice as a replacement or not?

Decoupling is usually 10-1000nF. 10pF isn't going to do much.

[Specmaster]

The first caps def leaked. The dented cap may have come that way from the factory.

That sliced cap though - maybe its just a decoupling cap and no one ever noticed?

The dented cap, could have come from the factory like that I suppose, but what would that have done to the capacitor rating? The scope looks as if it was made late 1990 or early 1991 and given its age and the possibility that this cap was compromised  at least because the dielectric insulation must be weakened by the dent, I'm surprised that it has not blown already?

As to the sliced cap, yes I think it is a decoupling cap as it sits across the output of an IC to ground, would a 10pf 100v ceramic disc capacitor suffice as a replacement or not?

Decoupling is usually 10-1000nF. 10pF isn't going to do much.

Yes your right, my mistake, I made a typo, it is in fact 100pf 100v. What is the best type of cap for this application?

[Specmaster]

You get them smaller than those from banggood, but maybe still too large.

Here is one that can sell you 2x4mm D15 L20.

https://www.aliexpress.com/item/1pcs-5mm-x-8mm-D15-L20-shaft-coupler-flexible-coupling-stepper-motor-encode-for-5mm-shaft/32670333088.html

You can also try with adhesive lined heatshrink tube.

These are a possible replacement, many thanks for searching them out, it need to be custom made version though to provide d1 2mm and d2 4mm.

I have already messaged Rich to see if he could offer assistance in sourcing the correct items, but in the event that he cannot help, then these could well be ideal.

[carl_lab]

...it is in fact 100pf 100v. What is the best type of cap for this application?

The defective one is a ceramic disk type, so I'd look for same type for replacement.

[Specmaster]

You can also try with adhesive lined heatshrink tube.

I have experimented with this idea and where the control is just a pot, this idea may have some merit provided nobody was ham fisted with the controls. Where there is a switch involved, then the resistance is just too much.

[TurboTom]

Varicap?? 

[carl_lab]

You can also try with adhesive lined heatshrink tube.

I have experimented with this idea and where the control is just a pot, this idea may have some merit provided nobody was ham fisted with the controls. Where there is a switch involved, then the resistance is just too much.

You can try multiple layers of heatshrink tube...

[Specmaster]

You can also try with adhesive lined heatshrink tube.

I have experimented with this idea and where the control is just a pot, this idea may have some merit provided nobody was ham fisted with the controls. Where there is a switch involved, then the resistance is just too much.

You can try multiple layers of heatshrink tube...

I did, I used 4 layers and the weak link is in the small gap between the 2 shafts.

[Specmaster]

Varicap?? 

I'm not sure, there is no mention of its type in the schematic and unlike some service manuals, there is no list of parts, part numbers or descriptions, so on this occasion I'm flying blind to a large extent as I've never seen any cap quite like this before. I did try and find out kind of cap is likely to be used in scope and I discovered that my initial thoughts of it being a ceramic disc cap was also borne out by carl_lab.

I attach the respective page from the manual and drawn a red circle around the circuitry in the area of the cap. Do you or anyone still feel that its a ceramic or varicap?

[tautech]

Ceramic cap, 100pF 50-100V NPO type.

It's listed as 100V but not sure why, I don't see anything on the schematic that indicates it need be. Maybe 100V versions were just easier to source. 

[Specmaster]

The on going struggle to locate suitable means of connecting the 2mm input shafts to the 4mm shafts of pots and switches on this has been a real pain so far. As you will have seen, there are solutions but they are very large scale and in some cases run the risk of grounding out on component leads etc soldered in on the PCB as well as being rather expensive to the point where you seriously have to question if the project is worthy of such expenditure on such antiquated equipment by today's standards? 

How about the following possible solution? whats your thoughts on this idea for hopefully a neat solution to the issue which further expands on the idea first forward by Tronde?

Using the direct shaft couplers from Ali Express (see attached picture) I could cut the coupler in half through the slightly narrower section and fit each half to the respective shaft and then heat shrink the 2 sections together? In so doing, both shafts would be gripped equally by the heat shrink being as the OD on the larger sections is 9mm so the turning effort exerted by the 2mm shaft from the front control knob would more in step with that transferred to the 4mm shaft of the pot so the heatshrink would be less likely to become screwed up because of the differences in the respective shaft diameters. Your thoughts please?