Any solder-ists fancy a challenge?

[Haz87]

Well... if you're any good, I imagine its hardly a challenge.

I have an old 80's Ford Roof clock (VDO stamped on the actual board) that requires repair. The display won't power up at all and having opened it up and had a quick look, all seems in reasonably good nick (tracks all healthy etc) bar very one obvious issue:

At first I thought it was sitting in a socket, however after the gentlest of prying, I believe these are purely spacers....which is annoying as it means I can't just pop it out, have a look at the back for a part number and swap out.

As I right royally suck at soldering, I wondered if there was anyone on here who knows their way round electronics of this sort and fancy having a go at de-soldering, sourcing and replacing the display?
If of course you want to confirm it is absolutely the display, I'd rather that - but as crap as Ford can be, I don't think the black smoke came as standard so imagine it is indeed the fault.

Pic of the back so its clear what is being dealt with:

I'm based in Essex but don't mind shipping it to anyone who is qualified or indeed capable of this kind of thing.

Cheers
Harry

 

[Parm]

@ajlelectronics ?

 

[dan treg]

not sure if helps but as its multiple pins maybe use hot air station rather than physically desoldering each pin

 

[6ply]

not sure if helps but as its multiple pins maybe use hot air station rather than physically desoldering each pin

If it's through hole I'm not sure that would help. We use one of these at work.

https://cpc.farnell.com/duratool/d00672/desoldering-station-uk-eu-plug/dp/SD01384

 

[voipio]

Sourcing vacuum fluorescent displays can be a right pain. Many are just not made any more. CPC, for example, doesn't seem to stock any at all.

Can you see the cathode wires, the ones running horizontally across the display, glowing when the module is powered up? The glow is very faint, and will probably need a darkened room to see it.

 

[Misterg]

bar very one obvious issue:

Do you mean the 'stain' in the lower right corner of the display?

I think that's just the 'gettering' that is added to maintain the vacuum. If it's still shiny and vaguely metallic looking, it's probably OK.

 

[Haz87]

Sourcing vacuum fluorescent displays can be a right pain. Many are just not made any more. CPC, for example, doesn't seem to stock any at all.

Can you see the cathode wires, the ones running horizontally across the display, glowing when the module is powered up? The glow is very faint, and will probably need a darkened room to see it.

Just powered it up in darkness, and I can't see any sign of life/light at all from the display. Not even a faint glow

 

[Haz87]

Do you mean the 'stain' in the lower right corner of the display?

I think that's just the 'gettering' that is added to maintain the vacuum. If it's still shiny and vaguely metallic looking, it's probably OK.

Yes that's what I was referring to. I'd assumed the connection inside had catastrophically blown causing remnants of smoke on the glass.
It does look shiny-ish. Just to confirm, it's internal to the glass - assume this still aligns with what you're saying?

 

[Haz87]

Yes that's what I was referring to. I'd assumed the connection inside had catastrophically blown causing remnants of smoke on the glass.
It does look shiny-ish. Just to confirm, it's internal to the glass - assume this still aligns with what you're saying?

Just googled gettering so now know that's exactly what you were getting at.

Ok cool - well guess it's less likely to be the display outright at fault.
Shame I still suck at electronics to suss what's next

 

[dan treg]

i would be inclined to look at the capacitor and transistor driver circuit it may or may not be the actual display

 

[voipio]

The three identical value resistors at top right of the board in the first few images might well be voltage dropping resistors for the cathode filament. They're wired in series, and have the same value, of 22 Ohms, as far as I can tell. Measure the resistance of each one in turn with a multimeter, to check if they give the same reading. Those resistors can have a habit of going open circuit.

 

[Misterg]

I'd assumed the connection inside had catastrophically blown causing remnants of smoke on the glass.

You know what it is now - that's exactly how it's deposited. When the display is made, it's in there as a wire or pellet. After the glass envelope of the display is evacuated and sealed, it is heated enough to vaporise it (either by passing current through a dedicated electrode, or by induction heating) and it deposits on the inside of the glass.

'Flashing the getter'

 

[Alan Reynolds]

So did the panel actually smoke and what was occurring when you saw this? If the display filaments are intact, I would tend to eliminate the actual display. Sourcing a display could be difficult. I would look at the passive components first. If the IC on the back, under that black blob is the culprit, then there is no way of repairing the panel.
It might be possible to source an LED 12volt clock of the same display size and substitute that.
Have you checked for any voltages on the incoming leads?

 

[Haz87]

The three identical value resistors at top right of the board in the first few images might well be voltage dropping resistors for the cathode filament. They're wired in series, and have the same value, of 22 Ohms, as far as I can tell. Measure the resistance of each one in turn with a multimeter, to check if they give the same reading. Those resistors can have a habit of going open circuit.

Have just checked all 3, and all reading bang on 22Ohms

 

[Haz87]

So did the panel actually smoke and what was occurring when you saw this? If the display filaments are intact, I would tend to eliminate the actual display. Sourcing a display could be difficult. I would look at the passive components first. If the IC on the back, under that black blob is the culprit, then there is no way of repairing the panel.
It might be possible to source an LED 12volt clock of the same display size and substitute that.
Have you checked for any voltages on the incoming leads?

No smoke seen. Clocks been fitted to the car forever and at a glance noticed it had gone off.

The connector in the car is fine (fuse and wiring were the first things checked).
I'm testing on a bench direct to 12v now anyway rather than keep climbing in and out the car.
Actual wires to the board are fine too - registering voltage at the solder joints on the board, so they aren't problematic.

 

[voipio]

Have just checked all 3, and all reading bang on 22Ohms

OK. Now, looking at image #4 in the original post. Check that the resistance between the top right and bottom left of the group of tinned solder pads, to which these resistors are soldered, reads 66 Ohms. One of the joints appears to have been reflowed, so there could have been a problem there before.

 

[Haz87]

OK. Now, looking at image #4 in the original post. Check that the resistance between the top right and bottom left of the group of tinned solder pads, to which these resistors are soldered, reads 66 Ohms. One of the joints appears to have been reflowed, so there could have been a problem there before.

Yup, 66Ohms.

Whilst I was probing, I've also checked voltage across them (the resistors not pads) and each is dropping 3v.
Voltage at incoming lead is 12.7, voltage at first resistor in, is 11.7(so a volt being dropped beforehand) and final resistor out is 2.8v (which seems very low to me but the fact they are all equal suggests this is right..)

 

[voipio]

At least that seems to rule out those resistors as being the problem. It also suggests that, if these are filament voltage droppers, that around 135mA is passing through those resistors, so the filaments may be intact.