Muter BMR 95 rejuvenator repair log

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Oct 032016

Had this for a while now and its been fantastic.

There Is a calculation outlined in the manual around predicting the life expectancy of the tube and ive made a little spreadsheet up to deal with that.
The calculation relies on being able to set the G1 voltage on the pot.

I noticed when I first got this that when I adjusted the G1 pot it was pretty loose feeling and also the reading bounced around everywhere.
Fast forward a year and I’ve come to use this again. I was completely unable to get accurate steady results from the G1 this time so I went to check the pot and found readings like this

I tried cleaning it out with contact cleaner but its had its day.
I ordered a new 250k pot from CPC and it came a few days later

Fitting this gave me solid results from the G1.

One thing I recently noticed about this rejuvenator is it has a switch marked “Soft” and “Strong”. Id not really noticed anything wrong with this before but the BMR 95 doesn’t have this option normally. It is present on the BMR 2005 model though.
Looking at it inside it looks to be a factory mod. The same wiring was used and its all part of the same loom. All solder joints look factory as well. Its either a factory mod or a very well done aftermarket mod. Either way Im pretty sure this give me the functionality of the BMR 2005.

 Posted by at 9:33 am

HP10529A repair log

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Jun 112016

Got myself a new HP logic comparator which had a fault on it.
The fault was with pin 11 on the LED’s.

The schematics for this are available but its so small its pretty easy to trace out just by looking at it.
Using the scope I found all the outputs of the 74L04 hex inverter at location U4 were stuck at around 1.7v. I replaced with with a 74LS04.

While I was poking around I also found the zener diode CR3 had a dry joint so resoldered that too.
Now its all working.

(Ignore the sound, had kids TV playing on Netflix while doing this)

 Posted by at 2:17 pm

Polar Toneohm 850 repair log

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May 282016

Last week I bought on Ebay an untested Polar Toneohm 850 (picture from Internet) :
For the uninitiated this is a instrument that is able to locate quickly and accurately shorts on PCBs.Device is essentially an audible milliohmmeter which, indeed, produces a tone whose frequency is inversely proportional to the resistance measured across its probes.The more you get closer to the short  and so the lower will be the resistance, the higher will be the produced tone.This is very useful when you come across a PCB with a dead short or small resistance between VCC and GND, using a normal multimeter would have no effect since you will end up to measure always same resistance values due its accuracy (most if times of 0.1 ohm ) which is too coarse.

So, I bought this kind of equipment which arrived me a couple of days ago.When I saw the package, I immediately had a bad feeling :


The box was broken and, once opened, the case of the unit too:


But worst , the unit didn’t power on at all, it was competely dead while the seller clearly stated (sending me also a picture)  that, although untested, instrument turned on showing numbers on display.

Since I needed this piece of equipment I opted for repairing it instead of asking for a refund and send it back.

I opened the unit and PCB was in untouched state, no sign of damage or burn components.DSCN3328

First of all I went to check voltages on the various test points, I could only measure few Millivolts.Thanks to the user ‘Fraser’ (thanks again!) on EEVblog forum I got schematics of this specific model so I could start my troubleshooting more confident.Design of the unit is quite simple : the 220VAC ( unit came with 120VAC line selected so  had to change it accordingly to my country) reaches the main transformer ‘T1’ being reduced to 9VAC then it got rectified by a couple of bridges and then regulated by a 7805 and  couple of 78L05 providing power for all the logic :


Again, I was able to measure more or less +1V on the inputs of the tree voltage regulators so problem was upstream, specifically in the main transformer (‘T1’ on schematics) :


Said simply, a transformer is a device made of a primary winding  and one of more secondary windings.Windings are usually wound around very high permeability ferromagnetic cores.A varying current in the transformer’s primary winding creates a varying magnetic flux in the core which is transferred to the secondary windings by magnetic induction.

So, my problem was clearly located in the windings.I removed the transformer:


I went to check windings with my multimeter and none of them gave me resistance values, they were almost all opened due the shock received during shipping!But luckily they were interrupted just near the pins, see picture of primary ones for example :


A bit of ‘surgery’ was needed using some AWG30 wire to restore all connections (part in excess of wire was cut, obviously)


Once mounted the transformer and reassembled all the pieces, the unit came back to life fully working!


Video below shows a testing on an arcade board where a 100nF by-pass ceramic capacitor was intentionally shorted:

 Posted by at 10:43 pm

Fluke 90 repair log

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Aug 232015

I’ve come to the conclusion that I will probably never own the 6809 pod for the Fluke 9010. Accepting this fact led me to find a Fluke 90 6809 tester.
These things are a far cry away from the capabilities that the Fluke 9010 offers but they still offer some decent functionality.

I got one of these from the US quite recently and it was, as far as I could tell, unused. It was still in its wrapping and is in pristine condition.
Ive got a couple of games that use 6809 CPU’s to hand so thought I would give it a try out.

I first pulled Breywood out and clipped the test clip over the CPU but I got an “ERROR 4 UUT CPU BUS REQUEST FAIL”. This means that the /HALT signal cannot be driven.
Its at this point I found the “Getting Started” guide online.
This states that the /HALT line cannot be tied to VCC. Breywood does indeed have this pin tied directly to VCC (and not even via a resistor).
Thinking about it I probably caused this fault by not reading the manuals prior to using it.

Time to break this thing open.

The Fluke 90 needs to be able to drive the /HALT pin and it also does a check on startup that it can do this. If it cannot drive the pin then it flags up the fail message.
As you can see in the above picture there are a few discreet components for this section. Doing some quick poking around with the logic probe revealed that the emitter on one of the NPN transistor (towards the top on the picture) was dead. I removed the transistor and checked it out of circuit, sure enough it was dead.
I replaced both of these transistors just in case and tested.

Everything now seems to be working fine.
I’m really pleased with this unit. It has some nice features like being able to set breakpoints (if connected to a PC)

 Posted by at 4:39 pm

Fluke 68000 POD repair log

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Dec 292014

Whilst doing some testing for Guddler over on the UK-VAC forum I thought it would be a good time to look into why I sometimes get a POD timeout error.
Normally when I get this error pushing down on the black cable that connects it to the 9010 fixes it.
Here is the reason why
One of the crimps had worked its way loose.

I carefully bent the small bard out a little and refitted. Now the POD seems to be rock solid.