Fluke 3092 200Mhz power problem

[JohnMcGivern]

Hi Bill, well stripped back down and looks like V1019 and v1016 are now open fuse is ok.
Will have to buy the 2sk119 (now obsolete) and the BUW12A will get 3v Zener as well.
There is so much in parallel I keep chasing my tail. I was testing cathode side of the diodes that where downstream of the T1 the top 5v line appears shorted anyway thanks for your help Bill. I not to sure about tackling the outputs with no load don't have enough experience.
I'll be working on this next Xmas haha. Best place to break into lines. Should I remove one coil at a time on output lines and test for short?
Many thanks.

[factory]

Originally Posted by WME_bill

Philips / Fluke 3092.
It is a pity there is no explanation at all upon the over-voltage or temperature protection circuits, in the PM3092 manual or any of the other manuals which use similar circuits.

Quite how you get 102ohms across that snubbing capacitor V1291 on the +56v rail is a mystery as Factory says.
wme_bill

The 102Ω across C1291 can be explained by the fact that both the capacitor & centre tap of the transformer winding are grounded, with the 100Ω (100E) resistor & the resistance of the transformer winding being measured as 102Ω.
If the capacitor measured 102Ω out of circuit, then it's shorted.

The description of the protection circuits is on page 365 of the PM3082 pdf, the trouble is how to determine which part is causing the shutdown without causing damage, same with trying to measure ripple voltages on the supply rails if it shuts down before you get a chance.
The over-voltage & thermal protection uses the +10VRef supply as the reference to two of the LM339 comparators. The under-voltage section isn't very clear which traces cross or join on the diagram.
The powerfail circuit allows the processor to save data when mains falls below 80Vac, it also shuts down the EHT-convertor, but it doesn't shutdown the PSU.

David

[JohnMcGivern]

Factory I haven't desoldered anything yet and as you say I cannot check voltages as it shuts down. Would it be possible to use a dim bulb and variac I/T or would it still shutdown just a thought. Would I damage anything?

[factory]

Originally Posted by JohnMcGivern

Hi Bill, well stripped back down and looks like V1019 and v1016 are now open fuse is ok.
Will have to buy the 2sk119 (now obsolete) and the BUW12A will get 3v Zener as well.
There is so much in parallel I keep chasing my tail. I was testing cathode side of the diodes that where downstream of the T1 the top 5v line appears shorted anyway thanks for your help Bill. I not to sure about tackling the outputs with no load don't have enough experience.
I'll be working on this next Xmas haha. Best place to break into lines. Should I remove one coil at a time on output lines and test for short?
Many thanks.

Has the power supply stopped squealing?

The +5V and some of the other rails use paralleled diode pairs, it is possible for one of pair to short if they are not well matched, is the rail still shorted with the PSU removed? If it is remove & check the rectifier diode pair & capacitors for shorts, the 5V transformer winding should be very low resistance.

David

[factory]

Originally Posted by JohnMcGivern

Factory I haven't desoldered anything yet and as you say I cannot check voltages as it shuts down. Would it be possible to use a dim bulb and variac I/T or would it still shutdown just a thought. Would I damage anything?

I'm not sure if it would still shutdown with a dim bulb (lamp limiter) as there is that under-voltage protection circuit, I wouldn't use a variac as they don't limit the current.

You say you haven't desoldered anything, did you not desolder the electrolytics to test them for capacitance value? What test equipment do you have for testing these? I can't help thinking it would be best to try some new ones in the rails that trip the protection, these are the +5V, +12V and -12V.
Edit: or maybe not, looks a nightmare to repair if you get problems with the SMD parts; https://www.eevblog.com/forum/repair...-oscilloscope/

David

[JohnMcGivern]

Yes I found that thread on eevblog I will order new caps for the rails you suggested. I used an esr meter they all measured less than 0.5ohms meter said good caps but maybe breaking down with higher voltage. I'll make a list tomorrow for the components.
Cheers.

[6.3volts]

Originally Posted by JohnMcGivern

Hi Dave, I have a 30v 3A PSU. I am using an Isolation TR and Variac I also have a dim bulb setup. I will take my time to try to understand this setup.

Many thanks Dave.

Just a thought. Some isolation transformers have continuity through their input/output earths. This can be dangerous when scoping as the scope ground is likely to be earthed too. Consider removing the through earth. I expect lots do it and lots consider that to be a bad thing. I've done it for years with no consequences.

[JohnMcGivern]

6.3volts, there is no earth connection, thank you.

[JohnMcGivern]

Just forgot to mention all electros installed at the moment are Nippon I have been all over this board tested every cap to gnd but it will be staring me in the face just like when you are doing a crossword. Bought other Ics from other vendors for later repairs.. Just listening to Dire Straits scope seems good haha.

[factory]

I noticed that on the eevblog post, hopefully longer lasting & better quality than the Philips ones used in the older PM scopes.

David

[JohnMcGivern]

Yes factory, I spent hours yesterday trying to source caps all the same make but I could not get the values I needed.
I had to use 33uF instead of 27uF I hope this will be ok It is borderline 27+-20% if not I will have to use a different make.
Also everything was supposedly in stock, this morning I was told delivery would be 5days, after I bought everything. I spent all the time to ensure everything was in Stock wasted my time.

[JohnMcGivern]

Well gents some of the components arrived today. Bill could you suggest what I could use for different loads on different rails as the power supply is out of the case and where to apply them. Should I apply them to the appropriate pins on the 32pin connector block. Should I use a lamp limiter with I/T and variac for reduced voltage or will this make the under voltage protection kick in this is all quite new to me so please bear with me if I suggest something stupid, many thanks. All the Best Gents and go Safe.

[JohnMcGivern]

All the Best for the Festive Season everyone, go safe.

Put scope back together. Connected to I/T and Lamp Limiter.
Turn on bulb lit bright, turned off immediately.
More checking came across a bodge on processor board Section5.3-13 bottom left of page but depends which manual as they are not the greatest this Manual 3092. I have enclosed a picture hope you can see it.
The chip is optional the footprint is there but instead of the chip a 10uF 50v cap
bridges pins 8 and 3 this is shorted. I am still trying to trace where these pins go to not familiar with these drawings.

Kind regards, John.

[factory]

The optional circuit is a clock IC with the usual 32kHz clock crystal.

To me that would be a short between the +5V Bat (battery) rail and ground (secondary side of PSU), the short horizontal lines shown on the diagrams are all ground points connected together.
If there is a short on the +5V bat rail the battery should be flat, unless one of the two diodes (V1279/1280) went open circuit.

What is the power rating of the lamp fitted to your lamp limiter?

David

[JohnMcGivern]

It's only 60watt light bulb.

[factory]

Ah looking at the specs the power consumption without options is 60W (max 80W), you may need a higher wattage lamp.

David

[JohnMcGivern]

Yep I'll up it to 2x60watt can't buy 100watt or above here only 60.

[WME_bill]

Philips Fluke 3092.
Power Supply test loads. The manual on page 8.9 gives a full loading arrangement and also shows the current which should be taken from each rail. There is no need to go so elaborate just to confirm if the primary side is working correctly. Take say 500ma from the +12 and -!2 rails. A couple of 25 to 30 ohm resistors will be quite sufficient.
With the knowledge of the current drawn from each rail, an ohmeter test across the output feeds into the rest of the circuit should give an indication if any rail is shorted and will help locate where the failure is.

You are very bold changing all the capacitors.
I am always chary of doing mass works like that as the pocking about om boards and soldering and resoldering seems to create other problems.
Clearly your faults at this stage are more than poor smoothing. You are probably looking for a failed transistor or diode, a shorted capacitor or burnt out resistor. When the unit is working more or less is the time to start chasing partly failed components.
David "factory" makes good points on 16 Dec. You have not confirmed that you are unsoldering one side of the capacitors before trying to test them.
wme_bill

[JohnMcGivern]

Bil I haven't changed any caps at present I just bought power supply caps as there was only 20 on the board apart from the large smoothing caps. Found shorted cap see posts33/34. I am just learning electronics and not up to speed with a lot of the terminology not to mention troubleshooting. Regarding load resistors I am wary as I have never done this before. See post 25 re eevblog. Many thanks.

[JohnMcGivern]

Factory, added 2x60w lamp holders now have 180w lamp limiter.
Checked batteries voltage was 3.12v.
What could have caused 10uF 50v cap to short, is the voltage rating enough.
Schottky diodes v1279/80 there are two values to pick from 30mA and 130mA rating service manual doesn't say.