Author Topic: Repairing an Old Hameg HM203-6 (not 203-7) - No trace: FIXED  (Read 19946 times)

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Offline tron9000

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Repairing an Old Hameg HM203-6 (not 203-7) - No trace: FIXED
« on: August 14, 2015, 03:45:33 pm »
Finally got the dust off  my Hameg I bought from a car boot sale about 2 years ago and forgot about it. I didn't have the space, then moved to a place where I had a garage, set up my little lab, plugged in the scope and checked there was a trace - which there was: good all still working!

closed up for the night and came back next day with some probes donated to me. Hooked it up to channel 1 and to the test signal - power on: nothing.

Tried to see if I could find the trace again, switched the triggering into AC, twiddled the trigger level till the Trigger LED came on yet no trace on screen. checked all button's like X10 mag, EXT trigger, all the daft things and still no trace.

Remove the probe, knocked the coupling on CH1 to GND, which should produce a flat line and adjusted the X & Y positions to see if i could find a trace - alas: fruitless!

The fact that the trigger LED comes on when I adjust the trigger level means that the signal is there. So I suspect that the display driver could be shot?

I have found a service manual (English, kindly shared on another forum):https://docs.google.com/file/d/0B87O0bRBiC6fUS1lUkM4cGVUNmc/edit?usp=sharing
users manual:http://www.manualslib.com/download/563302/Hameg-Hm-203.html

and have found these posts:
EEVBlog - https://www.eevblog.com/forum/testgear/old-analog-hameg-20mhz-dual-channel-scope-died-on-me-where-would-i-start/ - no conclusion to if he fixed it or not, have PM'd the OP.
Badcaps.net - http://www.badcaps.net/forum/showthread.php?t=28509

Guy on Badcaps say that the tube may be FUBAR'd - is this likely from what I've described? It may not be a problem as I have a Kikusui Scope which is just a CRT with X, Y adjust. It works but all that appears is a dot - it needs some signals in the back (i'll post pics if anyone's interested?)

I've added a pic attached of when it was working and stuck a sine wave into it.

So has anybody else got any advice or had experience they can share fixing this scope? Would save some time.

Cheers
« Last Edit: September 07, 2015, 08:10:19 am by tron9000 »
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Offline oldway

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Re: Repairing an Old Hameg HM203-7
« Reply #1 on: August 14, 2015, 07:42:40 pm »
Quote
Guy on Badcaps say that the tube may be FUBAR'd
For sure, it is not...its very rare :-+
Look for bad/cold solders, that's very common on these scopes.
Check the power supply .
Be carefull with high voltage !
 

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Re: Repairing an Old Hameg HM203-7
« Reply #2 on: August 14, 2015, 08:52:33 pm »
Quote
Guy on Badcaps say that the tube may be FUBAR'd
For sure, it is not...its very rare :-+
Look for bad/cold solders, that's very common on these scopes.
Check the power supply .
Be carefull with high voltage !
+1
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Offline tron9000

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Re: Repairing an Old Hameg HM203-7
« Reply #3 on: August 14, 2015, 09:54:54 pm »
phew well thats good to hear. Cos I really wouldn't like to break up the kikusui, its a nice tube and would like to turn it into a single channel scope as a project. Its got half the functionality, just needs a some x & Y inputs and its a scope!

Yep will be careful around the HV, thats a given. What voltage we looking at? 1000V?
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Online tautech

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Re: Repairing an Old Hameg HM203-7
« Reply #4 on: August 14, 2015, 10:09:12 pm »
What voltage we looking at? 1000V?
No.

You must work carefully through the scope, first checking ALL PSU voltages are to spec for both voltage and ripple.

From the low voltages the CRT voltages are derived, often by a switcher PSU, a common point of failure.

This is not a repair to hurry, let us all have a chance to download the Service manual and do some study.
You too.
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Offline tron9000

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Re: Repairing an Old Hameg HM203-7
« Reply #5 on: August 15, 2015, 02:57:44 pm »
What voltage we looking at? 1000V?
No.

You must work carefully through the scope, first checking ALL PSU voltages are to spec for both voltage and ripple.

From the low voltages the CRT voltages are derived, often by a switcher PSU, a common point of failure.

This is not a repair to hurry, let us all have a chance to download the Service manual and do some study.
You too.

no hurry, just wondered if anyone new off the top of their head.
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Offline oldway

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Re: Repairing an Old Hameg HM203-7
« Reply #6 on: August 15, 2015, 03:12:02 pm »
Power supply is very simple, low voltages of + and - 12V and +152V.
HV: -1975v....be careful, that is too high for multimeters, you must use an HV probe.
 

Offline tron9000

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Re: Repairing an Old Hameg HM203-7
« Reply #7 on: August 17, 2015, 08:26:52 am »
OK, so I've fibbed: Its a 203-6 not 203-7  :-[

somewhat embarrassing  :palm:, but still managed to get hold of a schematic and there's really not a huge amount of difference to the general block diagram. I googled my scope and looked a the pictures and picked the one that looked closest to mine and took the PN, rather than note the model number down before I left it the other night. :palm:

HAMEG HM203-6 service manual - most of its german, but all the schma is there.

Anyway I tested some of the voltages the other night, I've made a video, just editing to length.

But the jist of it is that I've tested the heater filament voltage, the intensity control voltage, and the filament to cathode (K ?) voltage and they all appear to be as expected.

(If you look at page 13 of the PDF) I've been measuring them differentially with a cheapo-meter on the PCB on the back of the tube . So measuring between -1877V and -1900V you would expect a 23V difference - which is what I got. Along with 6.3V AC on heater filament and about 33V from intensity control pot. The focus contol is a bit tricky and need to think a bit more carefully as the control pot is part of a large string of resistors connected to -1900V and GND.

So it think the best way of measuring this is to work out the voltage expected across the focus pot and measure the wiper from one end of the pot.

your also probably thinking: "why the hell are you looking at the HV stuff first!?" - well why not, gotta start somewhere, plus it was the most easily accessible place to start! which is actually somewhat concerning: you'd expect the HV to be the LEAST accessible!

Once I get the video done I pop it up here.

cheers
« Last Edit: August 17, 2015, 08:34:41 am by tron9000 »
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Offline firewalker

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Re: Repairing an Old Hameg HM203-6 (not 203-7)
« Reply #8 on: August 17, 2015, 08:30:26 am »
I had the same problem on my HM605. It was just a voltage regulator.

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Offline firewalker

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Offline tron9000

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Re: Repairing an Old Hameg HM203-6 (not 203-7)
« Reply #10 on: August 17, 2015, 09:16:48 am »
Cheers firewalker, will check for that.
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Offline oldway

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Re: Repairing an Old Hameg HM203-6 (not 203-7)
« Reply #11 on: August 18, 2015, 06:58:42 am »
First ajust intensity pot to max !
 

Offline tron9000

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Re: Repairing an Old Hameg HM203-6 (not 203-7)
« Reply #12 on: August 18, 2015, 08:00:49 am »
First ajust intensity pot to max !
did you watch the video?

I'll give it a try, would have to hack or fashion a new spindle for it. But I measured the intensity signal and it was as expected or is that not enough to test it?

Firewalker (Alexander) - I could not find that regulator and I also couldn't see any cracked joints on components that were in that area.

« Last Edit: August 18, 2015, 08:03:33 am by tron9000 »
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Online tautech

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Re: Repairing an Old Hameg HM203-6 (not 203-7)
« Reply #13 on: August 18, 2015, 08:15:04 am »
First ajust intensity pot to max !
Good spotting.  :-+

I'll give it a try, would have to hack or fashion a new spindle for it.
And you must, it is essential to have the Intensity control working.
Better still, replace the Intensity pot.

Not watched your vid yet, will wait until my broadband is under less load.
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Offline oldway

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Re: Repairing an Old Hameg HM203-6 (not 203-7)
« Reply #14 on: August 18, 2015, 12:14:31 pm »
Measure output voltages of horizontal and vertical amplifiers (or vertical and horizontal plates voltages)....beam is perhaps almost out of the screen and this can be a reason why don't see nothing on the screen.
 

Offline tron9000

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Re: Repairing an Old Hameg HM203-6 (not 203-7)
« Reply #15 on: August 18, 2015, 01:42:04 pm »
That would be another place to check.

Would you say points D1 through D4 on page 13 of HM203-6 schematic?
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Offline oldway

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Re: Repairing an Old Hameg HM203-6 (not 203-7)
« Reply #16 on: August 18, 2015, 06:13:18 pm »
Yes, D1 to D4 on the crt board but be carefull because there is more or less -2000V on this board.
 

Offline tron9000

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Re: Repairing an Old Hameg HM203-6 (not 203-7)
« Reply #17 on: August 19, 2015, 09:48:03 am »
I measured points D3 & D4 last night and fitted a spindle to the intensity pot (I removed the old spindle and just stuck a self tapper in the hole where the spindle was! Does the job!) and checked the intensity voltage levels whilst adjusting the the pot as well as testing the focus voltage levels whilst adjusting the focus pot.

  • Intensity range (measured between -1900V and pin 5 on back of CRT PCB) - 22V to 42V  DC approx
  • Focus Range (Measured between -1900V and pin 6 on back of CRT board - 5.4V to about 12V DC
  • D4 to 0V - 88V DC approx
  • D3 to 0V - 64V DC approx

NOTE: on the schematic, pg. 12, y final amplifier - points D4 and D3 are noted below each trace as ca +75V. so does this mean they should be in the region of 75V (as in circa 75v)? If so, then that's a bit ambiguous!

also another vid in the pipeline btw
« Last Edit: August 19, 2015, 09:50:15 am by tron9000 »
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Online tautech

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Re: Repairing an Old Hameg HM203-6 (not 203-7)
« Reply #18 on: August 19, 2015, 12:37:37 pm »
DC values on a schematic usually are referenced to a specific scope setup for those values to be valid.
RTFM
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Offline oldway

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Re: Repairing an Old Hameg HM203-6 (not 203-7)
« Reply #19 on: August 19, 2015, 04:02:48 pm »
Adjust vert. position pot. to have D3 and D4 more or less 75V
And D1 and D2, how much voltage ?
 

Offline tron9000

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Re: Repairing an Old Hameg HM203-6 (not 203-7)
« Reply #20 on: August 20, 2015, 07:42:33 am »
Adjust vert. position pot. to have D3 and D4 more or less 75V
And D1 and D2, how much voltage ?

Yeh I just read the users manual and it says to have the adjust vert pot to mid way, so I'd have had it just off centre probably

D1 & D2 - unfortunately, I haven't had time, got called away for Daddy duties. Should only take a couple of seconds to test, so will probably find out tonight.

Interesting thing though, Iread both manuals and only the HM203-7 has a section on operating voltages and Trouble shooting:
HM203-6 User manual
HM203-7 users manual

in the 203-7 manual, trouble shooting section I found a single sentence that may be relevant:
Quote
An absent trace in spite of correct plate voltages means a fault in the CRT circuit.

So if I do get the correct plate voltage on D1 & D2 and re-test D4 & D3 after adjusting the vert adj pot to centre, then that's probably the next best place to look.
« Last Edit: August 20, 2015, 07:49:29 am by tron9000 »
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Offline tron9000

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Re: Repairing an Old Hameg HM203-6 (not 203-7)
« Reply #21 on: August 21, 2015, 08:05:04 am »
OK Measured D3&D4 again - set the vert adj to mid way and yep: both were about 75V DC. Further twiddling and managed to get both to be 75V

D1 & D2: set the CH1 hor. adj. to mid way and both were about 68V DC.

So this does lead to a possible problem on the CRT circuit as the user manual says.

I've noticed on in the 203-7 schematic and manual it mentions a 22V blanking signal (supplied as a difference between the -1900V and -1877V). It looks like a delayed sawtooth or slow rising square wave form what I can gather.

without another scope, I think I'm stuck!
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Re: Repairing an Old Hameg HM203-6 (not 203-7)
« Reply #22 on: August 21, 2015, 08:53:12 am »
Quote
without another scope, I think I'm stuck!
Not yet, but often the case with CRO's you need another to fix them.

Will the CRT show a flash of a trace, dot or any signs of life when powered off and on, Intensity at max?

Does this Hameg have a Beam Find button?
Does that work?
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Offline oldway

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Re: Repairing an Old Hameg HM203-6 (not 203-7)
« Reply #23 on: August 21, 2015, 09:23:52 am »
OK Measured D3&D4 again - set the vert adj to mid way and yep: both were about 75V DC. Further twiddling and managed to get both to be 75V

D1 & D2: set the CH1 hor. adj. to mid way and both were about 68V DC.

So this does lead to a possible problem on the CRT circuit as the user manual says.

I've noticed on in the 203-7 schematic and manual it mentions a 22V blanking signal (supplied as a difference between the -1900V and -1877V). It looks like a delayed sawtooth or slow rising square wave form what I can gather.

without another scope, I think I'm stuck!
Have you tried in XY mode ?
With spot centered (D1 = D2 and D3 = D4), with -20V between cathode and wehnelt and I think you have the -1900V accelerating voltage (even if you have no way to measure it...you need a HV probe or a Avometer analog multimeter to measure that voltage), you should see a spot !

The only think you did not check, it is the heater continuity of the CRT.
Descharge first the HV capacitor, desolder on the crt board one of the 2 heating's wires of 6,3V coming from the transformer and measure the resistance between this wire and the place where it was soldered.
You must find a low value resistance, more or less 18R.
 

Offline tron9000

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Re: Repairing an Old Hameg HM203-6 (not 203-7)
« Reply #24 on: August 21, 2015, 11:39:22 am »
When powered on I can see a glow inside the tube -does that count? probably not!

I can disconnect the connector from the CRT PCB from the main PCB altogether, rather than desolder and check it.

Will try it in XY mode and see if that yields anything interesting.

I'm sure this scope does not have a beam find button.

There is sweet Fanny Adams when I turn it on and after it warms up, even with the intensity all the way up. No flashes or dots or anything.

To measure the HV, could I just build a big pot. div using say 10M 0.5W resistors?  I know its a bit Heath Robinson...
« Last Edit: August 21, 2015, 12:38:44 pm by tron9000 »
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Offline oldway

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Re: Repairing an Old Hameg HM203-6 (not 203-7)
« Reply #25 on: August 21, 2015, 02:19:50 pm »
Ok, if you see the heater glowing inside the tube, that's allright, you don't need to measure the heater resistance.

The  Hameg scopes don't have a beam find button.

You could try to tweak the VR501 trimpot and see if you have something on the screen.
Be careful, use a well isolated screwdriver because this trimpot is at high voltage (-1900V)
 

Offline tron9000

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Re: Repairing an Old Hameg HM203-6 (not 203-7)
« Reply #26 on: August 21, 2015, 02:42:21 pm »
Best crack out the VDE set I bought!  ;D
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Offline oldway

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Re: Repairing an Old Hameg HM203-6 (not 203-7)
« Reply #27 on: August 25, 2015, 08:28:55 am »

Why do you waste your time with useless and not interesting videos? |O

I asked you:
Quote
You could try to tweak the VR501 trimpot and see if you have something on the screen.
Why have you not done this ?

Want you really to fix this oscilloscope? :-//

We are trying to eliminate one by one all possible causes for which you have nothing on the screen:
- The supplies have been checked and are OK
- The high voltage seems to be OK (no way to measure it)
- Heating of the CRT looks OK
- The spot is at the center (D1 = D2 and D3 = D4)

Other voltages you measured have no interest because it can not help to have something on the screen.

It is almost impossible that the CRT suddenly become defective.

The only possibility would have been a defective open filament, but it glows so it's OK

Then, only the cathode voltage / Whenelt may still be responsible for the problem.
You measured this voltage and it is - 20V at max brightness
This is correct but without the blanking pulses, it is too much negative voltage for having a spot on the screen.
That's why I asked you to vary the trimpot VR501 with brightness potenciometer at maximum intensity so  to reduce the cathode voltage / Whenelt and see if you can see something on the screen.
If it's ok, that's mean that you have a blanking pulses failure.

Why do you not do what you are asked to do ? :box:
 

Offline TheBay

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Re: Repairing an Old Hameg HM203-6 (not 203-7)
« Reply #28 on: August 25, 2015, 11:17:00 am »
Totally agree with this Oldway!


Why do you waste your time with useless and not interesting videos? |O

I asked you:
Quote
You could try to tweak the VR501 trimpot and see if you have something on the screen.
Why have you not done this ?

Want you really to fix this oscilloscope? :-//

We are trying to eliminate one by one all possible causes for which you have nothing on the screen:
- The supplies have been checked and are OK
- The high voltage seems to be OK (no way to measure it)
- Heating of the CRT looks OK
- The spot is at the center (D1 = D2 and D3 = D4)

Other voltages you measured have no interest because it can not help to have something on the screen.

It is almost impossible that the CRT suddenly become defective.

The only possibility would have been a defective open filament, but it glows so it's OK

Then, only the cathode voltage / Whenelt may still be responsible for the problem.
You measured this voltage and it is - 20V at max brightness
This is correct but without the blanking pulses, it is too much negative voltage for having a spot on the screen.
That's why I asked you to vary the trimpot VR501 with brightness potenciometer at maximum intensity so  to reduce the cathode voltage / Whenelt and see if you can see something on the screen.
If it's ok, that's mean that you have a blanking pulses failure.

Why do you not do what you are asked to do ? :box:
 

Offline tron9000

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Re: Repairing an Old Hameg HM203-6 (not 203-7)
« Reply #29 on: August 25, 2015, 12:29:42 pm »

Why do you waste your time with useless and not interesting videos? |O

Why do you not do what you are asked to do ? :box:


right I'm trying to create a log of what I've done here and also practice a bit of video editing.
Quote
This was just looking at the voltages, which I already posted a few days back. Its just to show where they were and what I measured. nothing exciting!
^^ right there, this is not a progression, this is just a record!

How many people search forums for a solution to there problems? I'm doing this off my own spare time and trying to contribute here, pay a little back in the form of some findings, instead of just lurking! That such a bad thing? :box:

secondly, cos I got lead down a different avenue which actually lead to the problem! not that I don't appreciate the help, but where's the fire? does it look like I'm in a rush to fix this? does it bother you that much that I'm figuring some things out on my own? :box:

I decided to actually TEST the -1900V by measuring all the voltage drops across each resistor in the chain for the focus adjustment: and low and behold, came out at 94V ish!, which meant my original assumption was flawed.

Checked the 480V~ from the transformer: was present and was only after I left it on for 10mins I found that I could smell burning dust. I found that the opto: IC501 was really hot, took it out and tested the diode: reading came back as 0.133V both forward and reverse bias. Powered it on with the OPTO out and re-measured all the voltages between R507 to R521, guess what: 1900V!

So all I need is a new CQY80N to see if that fixes it and find out what else could have been taken out and why it caused the -1900V to collapse, if that is the culprit.
« Last Edit: August 25, 2015, 02:26:50 pm by tron9000 »
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Offline tron9000

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Re: Repairing an Old Hameg HM203-6 (not 203-7)
« Reply #30 on: September 06, 2015, 09:08:14 pm »
Right, just an update:

IT'S FIXED!! :-+

It was the opto-isolator, IC501!

Cheers to oldway & tautech.

As promised, the finer details, if your interested:
Entry #1 - Beginning & diagnosis
Entry #2 - Further Diagnosis - more fruitless searching
Entry #3 - Culprit found!
Entry #4 - Fixed!
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Offline BFX

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Re: Repairing an Old Hameg HM203-6 (not 203-7)
« Reply #31 on: September 06, 2015, 10:55:48 pm »
Good Job   :-+
It's nice unit I've also repair similar one recently. But it's not nice documented as yours.
https://www.eevblog.com/forum/repair/hameg-hm-203-double-trace-problem/msg484236/#msg484236

I have also next two from ebay for 50euro for repairing. It's relax for me  :D
« Last Edit: September 06, 2015, 11:06:33 pm by BFX »
 

Offline tron9000

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Re: Repairing an Old Hameg HM203-6 (not 203-7)
« Reply #32 on: September 07, 2015, 08:08:21 am »
Good Job   :-+
It's nice unit I've also repair similar one recently. But it's not nice documented as yours.
https://www.eevblog.com/forum/repair/hameg-hm-203-double-trace-problem/msg484236/#msg484236

I have also next two from ebay for 50euro for repairing. It's relax for me  :D

cheers! Your problem seemed a little more complicated than mine. Notice you mentioned that you used a home made pulse generator: what's it based on?
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Offline BFX

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Re: Repairing an Old Hameg HM203-6 (not 203-7) - No trace: FIXED
« Reply #33 on: September 08, 2015, 01:05:57 pm »
tron9000

It's very old function generator around XR2206 chip.
 

Offline tron9000

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Re: Repairing an Old Hameg HM203-6 (not 203-7) - No trace: FIXED
« Reply #34 on: September 09, 2015, 08:04:32 am »
It's very old function generator around XR2206 chip.

I'm thinking about building my own round one of those chips. Just something I can whip up and stick in a box.
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Offline BFX

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Re: Repairing an Old Hameg HM203-6 (not 203-7) - No trace: FIXED
« Reply #35 on: September 09, 2015, 10:39:55 am »
tron9000

I think better one is MAX038, but it's also vintage chip.
 

Offline tron9000

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Re: Repairing an Old Hameg HM203-6 (not 203-7) - No trace: FIXED
« Reply #36 on: September 09, 2015, 03:12:32 pm »
Jeez maxim..I'd have better luck finding a lesser spotted flying pig! :-DD
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Offline Stephan_T

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Re: Repairing an Old Hameg HM203-6 (not 203-7)
« Reply #37 on: September 11, 2015, 07:42:10 pm »
Best crack out the VDE set I bought!  ;D

Hi Chris,

are you aware, that the bare metal screw you use as a shaft for the intensity pot, is no where near VDE approval? According to the schematics, that pot also operates at high voltage (-1900V).
In one or two of your videos you showed how you found vagrant solder on the board. This could have likely been the root cause of the problem. Can you imagine what happens, if such a piece of vagrant solder finds its way between one of the contacts of the intensity pot and your conductive shaft screw?

Watching your videos gave me the impression that you underestimate the danger of high voltages.

Before you end your repair session, you may also check some of the adjustments. Especially the trim pods (VR501/VR502) around the intensity control may need some attention. The service manual should contain a procedure of how to set them.
 


Offline tron9000

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Re: Repairing an Old Hameg HM203-6 (not 203-7)
« Reply #39 on: September 14, 2015, 08:50:35 am »
Best crack out the VDE set I bought!  ;D

Hi Chris,

are you aware, that the bare metal screw you use as a shaft for the intensity pot, is no where near VDE approval? According to the schematics, that pot also operates at high voltage (-1900V).
In one or two of your videos you showed how you found vagrant solder on the board. This could have likely been the root cause of the problem. Can you imagine what happens, if such a piece of vagrant solder finds its way between one of the contacts of the intensity pot and your conductive shaft screw?

Watching your videos gave me the impression that you underestimate the danger of high voltages.

Before you end your repair session, you may also check some of the adjustments. Especially the trim pods (VR501/VR502) around the intensity control may need some attention. The service manual should contain a procedure of how to set them.

Far from it - I fully understand the dangers of high voltages, if I didn't I wouldn't be posting this, I don't think the afterlife has internet! :P

The mod I admit was on the fly and am relying on the insulation of the pot shaft, to which I am now compromising by jamming the screw in there. This will be replaced by super-gluing some plastic dowel in there instead.

I do note in the videos that there is high voltage and that you should proceed with caution and I always power off, make my test connections and then power back on and hardly even measure my test points directly with the probes.

I'll have a look at trimming those pots, but to be honest I think the intensity is unchanged, I'll have a read of the manual.

Thanks BFX for those links!

« Last Edit: September 14, 2015, 09:17:30 am by tron9000 »
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Offline misterno

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Re: Repairing an Old Hameg HM203-6 (not 203-7) - No trace: FIXED
« Reply #40 on: December 07, 2017, 06:38:48 am »
Dear friends,

i have a Hameg HM203-7 and before 2 days starts rolling the trace.
I did a video just to show the fault. Can you advise me where to start from?
TIA
VIDEO->https://youtu.be/0DVfRPy4IUI
 

Offline oldway

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Re: Repairing an Old Hameg HM203-6 (not 203-7) - No trace: FIXED
« Reply #41 on: December 07, 2017, 03:08:10 pm »
The failure seems to come from the power supply.

Check the small 1A bridges, they often fail with an open diode .... The rectified voltage is then too low for the regulator with a lot of 50Hz ripple.
 

Offline misterno

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Re: Repairing an Old Hameg HM203-6 (not 203-7) - No trace: FIXED
« Reply #42 on: December 07, 2017, 07:08:18 pm »
The failure seems to come from the power supply.

Check the small 1A bridges, they often fail with an open diode .... The rectified voltage is then too low for the regulator with a lot of 50Hz ripple.

I open the case and i disconnect all the wires. I took both the pcb's in my hand and do measurements. I 've checked all the important capacitors with capacitometer and i found one
electrolytic not connected well. I weld him well now. I also checked all the diodes and transistors. By my fault i 've destroyed one BF472 transistor.
I hope to replace it by late tomorrow.
I didn't check the small bridges you mention though. So i will do it tomorrow and post the results.
 

Offline misterno

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Re: Repairing an Old Hameg HM203-6 (not 203-7) - No trace: FIXED
« Reply #43 on: December 11, 2017, 06:03:13 pm »
UPDATE: I did change the broken BF472, i also measure the diode bridges too. I don't have a HT tester to measure the high voltage but i managed to measure
almost all the voltages from +12V to -12V, 135V, and 541V in the point says 500V. I 'm up to 41V as you can imagine.
What i noticed so far is that when i hit the tube gently near the neck, i get the trace line. When i try to increase the intensity, the line becomes brighter and after disappears.
Is it any possibility to have a damaged tube? Can i do anything more about it?
TIA
 

Offline Calambres

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Re: Repairing an Old Hameg HM203-6 (not 203-7) - No trace: FIXED
« Reply #44 on: December 11, 2017, 06:42:36 pm »
Reseat the tube connections and/or clean them.

Be very careful with the HT!

Offline misterno

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Re: Repairing an Old Hameg HM203-6 (not 203-7) - No trace: FIXED
« Reply #45 on: December 12, 2017, 06:24:19 pm »
Reseat the tube connections and/or clean them.

Be very careful with the HT!

I did that but no luck. Any ideas how to test if the crt tube is broken?
 

Offline IconicPCB

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Re: Repairing an Old Hameg HM203-6 (not 203-7) - No trace: FIXED
« Reply #46 on: December 12, 2017, 07:06:17 pm »
Are there any  resistors mounted on the tube connector?
Check them. generally high value resistors can go open circuit and affect bias voltages on the tube.
 

Offline misterno

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Re: Repairing an Old Hameg HM203-6 (not 203-7) - No trace: FIXED
« Reply #47 on: December 13, 2017, 08:02:36 am »
Are there any  resistors mounted on the tube connector?
Check them. generally high value resistors can go open circuit and affect bias voltages on the tube.
That's a good idea. I 'll do it later at evening. Thanks!
 

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Re: Repairing an Old Hameg HM203-6 (not 203-7) - No trace: FIXED
« Reply #48 on: December 13, 2017, 08:49:41 am »
I once had a CRO that drove me nuts with CRT behaviour so after mucking with it on and off I bit the bullet and reworked most of the EHT area, as with most CRO's it's the area of circuitry that's under the most strain, heat and voltage.
The high value resistors drift and go OC and any more than a M \$\Omega\$ or so are my first suspects. The DC restorer HV caps need be looked at too and they can be a bit hard to find from normal sources as 2-5KV caps are not that common now.
Last I bought were HV blue dipped disc ceramics from Aliexpress.

If the LV and HV (70-200V) rails are clean and to spec go looking hard at components under stress in the EHT (1-3KV) area as they have the greatest influence on CRT performance.
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Offline misterno

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Re: Repairing an Old Hameg HM203-6 (not 203-7) - No trace: FIXED
« Reply #49 on: December 13, 2017, 07:41:28 pm »
I once had a CRO that drove me nuts with CRT behaviour so after mucking with it on and off I bit the bullet and reworked most of the EHT area, as with most CRO's it's the area of circuitry that's under the most strain, heat and voltage.
The high value resistors drift and go OC and any more than a M \$\Omega\$ or so are my first suspects. The DC restorer HV caps need be looked at too and they can be a bit hard to find from normal sources as 2-5KV caps are not that common now.
Last I bought were HV blue dipped disc ceramics from Aliexpress.

If the LV and HV (70-200V) rails are clean and to spec go looking hard at components under stress in the EHT (1-3KV) area as they have the greatest influence on CRT performance.
UPDATE: I did check the resistors near tube, capacitors, diodes. I did find an open 22ohm resistor R3027 near optocoupler. I did change it but no luck.
Also i did find almost all the voltages corect except HT that i didn't have appropriate probe to measure it.

Is it possible to show me from the schematic, which components should i change too and from in EU i can order them?

Here is the schematic of my HM-203-7  ->https://mega.nz/#!FdZmTa6a!BbGdrKCm1gZLqHX_HqLlNPFyzrR7gzN4L9H-KmAN0uA
« Last Edit: December 13, 2017, 07:43:56 pm by misterno »
 

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Re: Repairing an Old Hameg HM203-6 (not 203-7) - No trace: FIXED
« Reply #50 on: December 13, 2017, 08:11:55 pm »
UPDATE: I did change the broken BF472, i also measure the diode bridges too. I don't have a HT tester to measure the high voltage but i managed to measure
almost all the voltages from +12V to -12V, 135V, and 541V in the point says 500V. I 'm up to 41V as you can imagine.
This would seem to point to a strong clue.....too much current drain on the EHT.
Components to check are in the EHT section of the PSU and those subjected to the EHT supply on CRT section of TB-Board. You may need a HV meter to check the differential voltages in parts of that circuit.

The voltage differentials between elements of the CRT are crucial for a stable and predictable display.
I had the differential zener fail in a CRO (D312/313) once and it upset things immensely.
Work slowly and methodically through tests and replace any component that you suspect faulty.
Avid Rabid Hobbyist
 

Offline misterno

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Re: Repairing an Old Hameg HM203-6 (not 203-7) - No trace: FIXED
« Reply #51 on: December 18, 2017, 10:39:19 am »
I spend all the weekend trying to fix this device. I take out ALL transistors and measure them with a transistor meter. All was good.
Then i did resistor measurement by took on leg in the air and i found that one of them (R3019 in PSU page) was 470K instead of 3K92 as you can see in picture.

I 've measured ALL the electrolytic capacitors too. Everyone was OK. Same with the diodes and big nf capacitors too.
I 've checked the pages and mark the components with yellow pen.

After that, i changed the faulty resistor, i did re-assembling all the PCB's, wires, etc.
Now when i switch on the device, i get very low intensity screen and no trace line at all.
The good part is that now the screen don't affected by small hitting the neck of the tube as did before repairing.
Today (i hope) i will do voltage measurements and post the results here.
« Last Edit: December 18, 2017, 10:44:20 am by misterno »
 

Offline misterno

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Re: Repairing an Old Hameg HM203-6 (not 203-7) - No trace: FIXED
« Reply #52 on: December 19, 2017, 07:45:41 pm »
UPDATE: Finally i did fix it. Now this old but very useful oscilloscope, works again. As i 've tested almost all critical components, i found a broken wire that looks well, an open resistor in PSU and finally a small ball of weld which made a short circuit to the HT area.
Component tester works well too. I have a small difference in 1KHz test signal and i would appreciate if you can tell me if i can adjust it well.
Thank you for your replies so far.
 

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Re: Repairing an Old Hameg HM203-6 (not 203-7) - No trace: FIXED
« Reply #53 on: December 19, 2017, 09:36:07 pm »
UPDATE: Finally i did fix it. Now this old but very useful oscilloscope, works again. As i 've tested almost all critical components, i found a broken wire that looks well, an open resistor in PSU and finally a small ball of weld which made a short circuit to the HT area.
Component tester works well too. I have a small difference in 1KHz test signal and i would appreciate if you can tell me if i can adjust it well.
Thank you for your replies so far.
Well done.

How do you know the 1 KHz is out ? Have you put a counter to it ?
Some CRO's can be adjusted/trimmed to 1 KHz but for most use it doesn't matter.
The fast edges are what matters and the approximate frequency and amplitude are only needed as sanity checks.
Near enough is good enough for the probe cal output.
Avid Rabid Hobbyist
 

Offline misterno

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Re: Repairing an Old Hameg HM203-6 (not 203-7) - No trace: FIXED
« Reply #54 on: December 20, 2017, 09:41:47 am »
In this case i will prefer to close the cover and start using the device. Thank you again for info's and help.  :D
 

Offline GreyWoolfe

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Re: Repairing an Old Hameg HM203-6 (not 203-7) - No trace: FIXED
« Reply #55 on: December 20, 2017, 02:25:30 pm »
Congratulations.  Take pride in your repair and enjoy the scope. :-+ :-+
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