Vintage Hameg HM307 scope

[Phil1977]

Hi,

got good luck at ebay: For the price of a not too fancy 2 person dinner I got an old Hameg HM307.

After some basic cleaning it proofed to be in absolute pristine condition. There are absolutely no "burnmarks" or convection traces inside and also the functionality seems to be fine. The CRT is bright and quite well focusable (it looks worse in the picture as in reality), all the switches are working without free play, even the potentiometers seem to be quite free of noise.

Beside just making my joy about this acquisition public I have two questions:
- Is it worth to recap anything? As I said, everything works fine, it seems that caps in this type of circuit aren't stressed very much and I hope they wouldn't fail in an explosive way. I couldn't see anything like the infamous "RIFA"-caps in the mains connection.
- The input amplifier uses 2 possibly matched JFETs in this fancy ceramic housing with gold contacts. In the schematic they should be TIS69, on their housing they are BF245A. Is this of any concern?

The scope works well up to around 5MHz.

I want to use it for a DIY CV/CC curve tracer, so I don't need more than 100kHz.

[Zenith]

I don't know about this model, but in later Hamegs, HM203-5/-6/-7, HM605, I've found the electrolytic capacitors in the power supply (Cosonic brand) have always been troublesome, to the extent that I change them routinely. Other than that, I don't think automatically fitting new capacitors is a good idea, for most equipment. You can probably leave them alone, but if it starts to act up, check the power supplies, which is essential when troubleshooting any electronics, and don't be surprised if the capacitors need changing.

BF254A looks like a superior replacement for TIS69, which has probably been obsolete for a very long time. Makers often substituted one part for another in the course of production. Hameg weren't good at documenting changes they made. They were probably matched, because FET characteristics within a type, are notoriously variable. It's quite common to see a monolithic matched pair in that position, but this would have been an introductory scope.

[Phil1977]

I don't know about this model, but in later Hamegs, HM203-5/-6/-7, HM605, I've found the electrolytic capacitors in the power supply (Cosonic brand) have always been troublesome, to the extent that I change them routinely. Other than that, I don't think automatically fitting new capacitors is a good idea, for most equipment. You can probably leave them alone, but if it starts to act up, check the power supplies, which is essential when troubleshooting any electronics, and don't be surprised if the capacitors need changing.

There was one important thing to do with this device: Re-bridge the transformer from 220V to 237V.

The buffer capacitors in that unit passed ESR testing and don't get warm in operation. Close inspection of the boards with the thermal imager after 25min of ontime showed some frightening hot transistors (around 100°C), some not so frightening but anyhow hot power resistors (also around 100°C) but no "glowing" tantalums or other components that are not supposed to dissipate power - or if there are any, they have well hidden themselves from the FIR-lens 

For nowadays standards it´s crazy how much construction effort went into an introductory scope of this time. Of course it´s technique is very simple, but it doesn't seem bad at all. And as long as you can't buy a dead-time free XY integrator with a low-latency TFT for that price I even think it can be of some use today.

[pdenisowski]

I don't know about this model, but in later Hamegs, HM203-5/-6/-7, HM605, I've found the electrolytic capacitors in the power supply (Cosonic brand) have always been troublesome, to the extent that I change them routinely. Other than that, I don't think automatically fitting new capacitors is a good idea, for most equipment. You can probably leave them alone, but if it starts to act up, check the power supplies, which is essential when troubleshooting any electronics, and don't be surprised if the capacitors need changing.

My HM407 still has all the original caps .... fingers crossed

[Zenith]

They are 1000µF 35V capacitors which are 20mm high. 25mm high will just about fit when the case is replaced. It really needs capacitors which are 23mm high or less. That makes them a little harder to source.  If I haven't replaced them as soon as I got the scope, I've found that shortly afterwards, I've had to.

There are other capacitors in the power supplies which are 47µF, 25V from memory. They can also fail and you have ripple at several MHz and 1V ptp on the power lines. They are hard to replace without removing a PCB, which is quite a lot of work.

Apart from that, I've had no particular problems with capacitors in Hamegs.  I've come across cracked soldered joints quite often, and problems with switches which needed cleaning, which is to be expected in a scope over 30 years old. What I have found with Hamegs is that the scope can be different from the available manuals, and in particular the Y pre-amps and final Y amps may have gone through a few revisions before they were finalised. The documentation for the early versions is hard to find.

I'm not familiar with the HM307. It looks different in construction to the HM 203, HM 605 and HM1005 scopes I've worked on. If it contained those 1000µF 20mm high capacitors, I'd change them.  Otherwise I can see no point in replacing capacitors without a reason.

[blackfin76]

My HM407 still has all the original caps .... fingers crossed

I used to have a HM407, such a nice fine trace it had. Never used the digital function but the analog part was very nice.

Sold it off a couple of years ago since I have too many scopes 

[egonotto]

My HM407 still has all the original caps .... fingers crossed

I used to have a HM407, such a nice fine trace it had. Never used the digital function but the analog part was very nice.

Sold it off a couple of years ago since I have too many scopes 

Hello,

You can never have too many scopes. At most, you have too little space.
I still own a 7 cm HM207 that is stored at a friend's house.

Best regards
egonotto

[EvgenyG]

My HM407 still has all the original caps .... fingers crossed

That is a HM407-2, which is different to the original HM407. I've done a full recap (136 caps) + replaced all rotary encoders on a HM407, I know
Speaking of HM407, it is a great scope. Autoset is SUPER quick. Digital is probably only useful for roll mode which has a super smooth scrolling. LCD scopes can't match that.
Also, acceleration voltage is only 2kV but the trace is super fine and bright.