Blackstar 4503

[mendip_discovery]

So today I was asked to look at a Blackstar 4503. The readings are way off, and the readings seem to wander about a bit.

I tried a DC V 2 Null and it fails. I suspect it is because even with a short it wanders up and down.

It is for a customer, and they still use it and they need that as the software they use needs that meter.

I guess this is one from 1995 ish going by some date codes I have found.

I suspect 1 or more caps and maybe the battery as being part of the issue. Though the battery measures a healthy >2.5V so even though its puked up its still alive...for now.

[mendip_discovery]

More pics

[mendip_discovery]

last lot,

[TheNewLab]

replace battery. even though voltage measurement may tell it's good, visibly it is not. (issues, no or low current, and cap bleed shorting or opening circuit on traces  near or under battery) For Bulging caps, best to just replace. only a couple there, right?

[mendip_discovery]

I got a moment to play with the meter today.

After fighting with the board I managed to coax it from its comfy shell. I replaced 2 caps, 1 of which was on my worry list. This seems to have fixed a few things as most of the ranges now are a little more settled. After a NULL session all was good except for the 4V range which is a bit of a wandering thing. After powering on for 10 mins I could not do another auto zero as it gets stuck at the 4V range.

I think it's going to need a full recap, and I needed my solder sucker to get the battery out.

[edpalmer42]

I have a 4503 that's working okay, but the battery needs replacing.  I'm seriously thinking about replacing the 2V4 battery with a 3V6 battery.  The RAM chip's minimum spec for data retention is 2V0 and the circuit has a diode between the battery and the chip.  The 2V4 battery is too close to the edge even when fully charged.

Since you're looking at the same battery replacement, have you considered something like that?

Ed

[mendip_discovery]

I have already bought a Varta V150H 2.4V NiMH Button Rechargeable Battery 150mAh from RS. Ordered at 7pm lastnight in the office by the time I got back from my job I had to do today.

I took some more pics today just for the records. Though I suspect TiN is grinding his teeth at the standard of the photographs I have done already.

[AVGresponding]

When you've cleaned the board, clean it again. Then clean it again... this was the lesson from Specmaster's adventure with a 4503. That electrolyte gets everywhere, under ICs and up transistor legs, it's a real nuisance.

I got lucky with mine; the battery died without leaking, so I just had a CALErr and tOtErr (total loss of calibration data), which was easily sorted out once I bodged in a new battery (2x AAA Ni-MH LSD).

[mendip_discovery]

I'm a little concerned about the condition of the two things which look like boild sweets that I assume are caps. The ones near the craddock and the battery.

I dont think any of the electrolitic caps have leaked, just swollen a bit.

More pics and playing tomorrow. I am meant to be recouping overtime but I want to fix things. It makes me feel warm and fuzzy for the weekend. One day i will get my own 1281 fixed.

[Audiorepair]

The leaking battery has deposited corrosive liquid around a via next to the "Craddock" which looks like has a trace to this Craddock.

I would be hard wiring this via and its connections.

And I don't know what these "boiled sweets" are meant to be or why you might think they have a problem.

I think you might be referring to the polystyrene caps.  Its is unlikely these are faulty.


And I don't think we need any more pics for now.

[lowimpedance]

I'm a little concerned about the condition of the two things which look like boild sweets that I assume are caps. The ones near the craddock and the battery.

Those silver caps near the CADDOCK divider are indeed polystyrene and from the pic there does appear to be corrosion on the leg and pad of the one in the middle, I would replace that one at least.
As AVG noted the contamination must be fully removed, make a careful note of any affected component ,legs pads etc, and tracks.

[Specmaster]

When I got my 4503, I had very similar problems and the resistances ranges were useless, and it was all down to the battery leaking just like yours has. Personally I'd 100% replace the battery with the same, but I'd take it out of circuit first and don't worry about losing the calibration data, it is fairly easy but time-consuming to do a self calibration and adjustment via the front panel, just follow the instructions in the service manual. You don't need the equipment they tell you to use, all you need is another meter that you know is in spec and some reasonable stable voltage, resistance and current references, and then you can tweak the 4503 readings by following the instructions until you can get readings that match the known meters.

Once you have the battery removed, thoroughly scrub the board on both sides many times with some 70% Isopropyl and dry carefully. Repeat this many times especially in the area around the battery location and the corner quarter of the board where the Craddock precision resister network is located needs extra attention as this area is extremely high impedance as its the meter inputs section and any contamination in this area will screw the meter readings. Also, I'd do a full recap of the board as even though they don't look bad, they are the original caps and many of mine were found to be dry and way out of spec.

Those boiled sweet looking polyester caps and the resistor by the battery are showing badly compromised leads and solder joints, which mine did as well. I'd clean them up, de-solder them and check them, and either replace them or if they are OK and you can clean the legs up OK enough to be able to tin them. Pay particular attention to holes that the leads of the caps pass through and make sure that are clean and the via's, pads and connecting traces are not compromised and repair as needed. Only when you have cleaned the board loads of times, fit the replacement battery, and then test and the readings seem to be more stable, do a recalibration via the front panel and then hopefully you will have fixed the meter, they are worth the extra work.