Author Topic: Documentation for restoring a PM3261  (Read 1984 times)

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Offline PlatinumX

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Documentation for restoring a PM3261
« on: November 24, 2015, 08:23:01 am »
Hi!  I just bought a Phillips PM3261 to restore, and while I found a PM3260 service manual, it's a bit different from mine.

I haven't gotten deep into the guts yet, but just based on the controls, the areas that are missing from the documentation are:
  Event Counter - this is broken on mine, or I don't know how to use it.
  Digital Delay - this is also broken and/or too mysterious for me.  All it does is turn off the delay mode.

If anyone has any info or documentation that could help, that would be great!
« Last Edit: November 24, 2015, 10:24:05 am by PlatinumX »
 

Offline tautech

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Offline lowimpedance

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Re: Documentation for restoring a PM3261
« Reply #2 on: November 24, 2015, 10:55:56 am »
Will upload the scans when back at work tomorrow!.
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Offline lowimpedance

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Re: Documentation for restoring a PM3261
« Reply #3 on: November 24, 2015, 10:33:46 pm »
Okay the scans are from the PM3261 handbook but not the whole book just the schematic, parts overlay, some operating instructions etc.
Check the quality is good enough.
I can do higher dpi scans if needed and also more of the handbook if needed, (note ; its quite a bit more to scan which is why I did not do the whole thing!).

edit: I should point out that the old CRO at work was labeled PM3261, the handbook's supplied were for the PM3260 main frame and the PM3261 supplement !.
« Last Edit: November 24, 2015, 11:15:38 pm by lowimpedance »
The odd multimeter or 2 or 3 or 4...or........can't remember !.
 

Offline PlatinumX

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Re: Documentation for restoring a PM3261
« Reply #4 on: November 25, 2015, 08:54:38 am »
Wonderful!  Thanks so much, lowimpedance.  I'll try my best to document the repair and let you all know how it goes.
 

Offline PlatinumX

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Re: Documentation for restoring a PM3261
« Reply #5 on: November 26, 2015, 07:45:48 am »
Just took my first crack at it.  My board doesn't quite match the diagram and has quite a bit of rework - cut traces, additional components, etc.  I suspect it is from an early production run (date codes are all circa 1975).

I found the following:

Probed voltages in circuit and found that the +5V rail was at 0.81V while +6V rail was at 5.86V.  Measured about 319 ohms from +5 to ground, so I suspected a bad diode.  Took the board out and removed the diode (GR2401) and it tested good.  Took out C2406 and C2308 and tested capacitance and leakage resistance, tested good.  Put the diode and caps back in and re-installed delay board to do additional probing, and found +5V is now 4.92V and counter now turns on.

Tried to perform delay calibration per section 3.1 of lowimpedance's PM3261-c.pdf.  Found that the count knob push-pull had dirty contacts, which was leaving it in "fast" mode and couldn't hit the count speed spec (item 7).  Blew it out with compressed air and it now works much better.  Now meets spec at 15.5 seconds / 10 count.

My guess as to how this is supposed to work is it just delays the display by N trigger events (N being from 0-9999 as displayed on the counter).  This is similar to how the "Delay Time" knob works, but it's better because it's can scan through data(?)  There's a press release describing it here: http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=5183165.

However, I only get a trigger when the counter is 0 or 1.  Outside this range the "NOT TRIG'D" light comes on and sweep stops if displaying the delayed timebase, or the trace highlight goes away if displaying main TB.

I think I need to understand Fig 3.5 of PM3261-c.pdf more fully before continuing.
 

Offline PlatinumX

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Re: Documentation for restoring a PM3261
« Reply #6 on: November 28, 2015, 05:16:31 am »
@lowimpedance, could you do me a favor and get a high-DPI scan of Page 28, Fig. 3.1 as shown in the attachment?

It looks to me like the delay board is now working as expected, but it's not seeing trigger pulses from the delayed trigger time base.  It looks like they reworked in a transistor to generate the pulses, but it's not shown in the circuit diagrams I have and I suspect it's lost a wire.

I've shared all the documents I have here: https://drive.google.com/folderview?id=0B3jtpt2_4iKFSnY2VFN1Q2NlV0U&usp=sharing
 

Offline lowimpedance

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Re: Documentation for restoring a PM3261
« Reply #7 on: December 03, 2015, 11:56:41 pm »
Higher DPI scan of fig 3.1 as requested. (jpg) Hope it has enough resolution.
Forum limited to 1M per upload !! 
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