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[Kevin Wood]

Used to be OK, but I'm cautious about PCBs.  From what I can see, it's all been hand-soldered, so it should be possible.  (I don't actually mean hand-soldered, but it definitely hasn't been built using the techniques they use today - can't remember the right term.) 

Mind you, my shaky hands and deteriorated eyesight are going to slow me down a bit!   Definitely a kitchen table job.

Well, you could just change the diodes. Not sure what the existing ones are but something like a 1n5402 or better ought to do the job (Maplin code QL83E). Make sure you get them the same way round as the existing devices.

Kevin

[jereboam]

Used to be OK, but I'm cautious about PCBs.  From what I can see, it's all been hand-soldered, so it should be possible.  (I don't actually mean hand-soldered, but it definitely hasn't been built using the techniques they use today - can't remember the right term.) 

Mind you, my shaky hands and deteriorated eyesight are going to slow me down a bit!   Definitely a kitchen table job.

Well, you could just change the diodes. Not sure what the existing ones are but something like a 1n5402 or better ought to do the job (Maplin code QL83E). Make sure you get them the same way round as the existing devices.

Kevin

Right!  The lad has carefully sorted out the wiring (he even labelled the wires) and the beast is on the living room floor.  The next job is to clean it up, remove the base panel and clean up what's under there.  Then I can remove the two dodgy diodes and take them down to Maplins to see if they can match them.  If not, I'll just get the type you mentioned, the 1n5402.  According to the Maplin's website, Ipswich has 5 in stock, so I'll probably clean them out - it's a long time since I soldered anything onto a PCB, so I may incinerate the first one.  Hope I don't damage any other components.  I've got a solder sucker somewhere, so I think it might be sensible to have that on hand before I start, but I should be able to manage without.  I'll get the lad to assist. 

By the way, when you say "1n5402 or better", what does better mean?  The 1n5402 is rated at 200v but there are others with higher voltages.  Apart from that, it looks to me like "a diode is a diode is a diode".  OK, rectifier diodes.  I appreciate that there are other types.

[Kevin Wood]

Yep, I meant 200v PIV or better. Without knowing the amp in question I would guess the DC supply is no more than 50 or 60 volts and, as a rule of thumb, the diodes will see roughly double that so 100v might be a bit marginal, so next one up. Of course, if you end up with 800v devices it won't hurt.

I would be inclined to replace all 4 diodes while I'm there. The originals look like pretty puny devices.

Kevin

[jereboam]

Yep, I meant 200v PIV or better. Without knowing the amp in question I would guess the DC supply is no more than 50 or 60 volts and, as a rule of thumb, the diodes will see roughly double that so 100v might be a bit marginal, so next one up. Of course, if you end up with 800v devices it won't hurt.

I would be inclined to replace all 4 diodes while I'm there. The originals look like pretty puny devices.

Kevin

It's actually a dual-supply unit - you can run it off a 117v DC supply as well, I think.  At least, that's what it says in the manual - still got it after all this time - amazing.  The 1.5A fuse should be replaced with a 2A fuse if running on 117v, it says on the back.

Replacing all 4 diodes seems like a good idea - I was going to ask you about that.

Will let you know how I get on a bit later.

[Chris_H]

I'm with the capacitor argument.  There are some big electrolytics in there and they like to dry out over time.  Possible they have taken the diodes out so buy extras if you're replacing them first!

I would remove the capacitors and check them with the DMM.  Just don't keep the soldering iron on the copper tracks for too long or they'll lift.

[Kevin Wood]

I agree that any electrolytic that old would be a concern. If it were mine I'd probably be replacing them as a matter of course, TBH. At least, it's worth looking for any signs that the capacitor cans have started to bulge.

<squeamish look away now> I actually have an extension lead with a bulb holder wired in series for firing up devices like this after repair. Stick a 60w bulb in series with it and it limits the fault current so, if something else is wrong, you can investigate it without "letting the smoke out".

Kevin

[Debs.]

I agree that any electrolytic that old would be a concern. If it were mine I'd probably be replacing them as a matter of course, TBH. At least, it's worth looking for any signs that the capacitor cans have started to bulge.

<squeamish look away now> I actually have an extension lead with a bulb holder wired in series for firing up devices like this after repair. Stick a 60w bulb in series with it and it limits the fault current so, if something else is wrong, you can investigate it without "letting the smoke out".

Me too! .....a variac and an in-series lamp base (used with a variety of wattage lamps).

Sadly, I`ve had too much experience with 'smoke generators'.

[jereboam]

As I said, I'm going to clean Maplin out of diodes.  I'll replace the two duds, then test.  If all is OK, I'll replace the other two.  If it's not, then I've got spare diodes for attempt 2.

The big electrolytics all look good, and I've felt all round them - no lumps or bumps.  I wouldn't have the first idea how to test them anyway. 

Do I need to use your suggested light-bulb technique?  I haven't got smoke, there's no smell of burning anywhere and the major symptom is a blown fuse.   The fuses come in packets of 10 and I've got 9 left!

But it's all on hold for today - I'm trying to work out how to remove the headlamp unit from a Peugeot 205 - all the wiring seems to have fallen off the back and it's completely inaccessible because of the fuse box bracket.  And it's freezing and drizzling out there.  And the local garage aren't answering the phone.

[jereboam]

When I said freezing, I hadn't read the weather bulletin from our Snowdonia correspondent.

My duff headlamp and drizzle pale into insignificance compared with a busted radiator and 12" of snow!

Good luck out there!

[Chris_H]

As I said, I'm going to clean Maplin out of diodes.  I'll replace the two duds, then test.  If all is OK, I'll replace the other two.  If it's not, then I've got spare diodes for attempt 2.

The big electrolytics all look good, and I've felt all round them - no lumps or bumps.  I wouldn't have the first idea how to test them anyway. 

Do I need to use your suggested light-bulb technique?  I haven't got smoke, there's no smell of burning anywhere and the major symptom is a blown fuse.   The fuses come in packets of 10 and I've got 9 left!

But it's all on hold for today - I'm trying to work out how to remove the headlamp unit from a Peugeot 205 - all the wiring seems to have fallen off the back and it's completely inaccessible because of the fuse box bracket.  And it's freezing and drizzling out there.  And the local garage aren't answering the phone.

Faithful DMM on a lowish Ohms range.  Connect red lead to positive and black lead to negative (probably best to short capacitor to make sure it's discharged first).  DMM reading should start low and whizz up to very high Ohms or overload.  A lot of old analogue MMs put positive out on the black lead and vice versa but at that low voltage it probably wouldn't hurt a big fat cap like that.  If it sits at a steady low resistance reading then it's kapputt.

[I_want_an_Omega]

As I said, I'm going to clean Maplin out of diodes.  I'll replace the two duds, then test.  If all is OK, I'll replace the other two.  If it's not, then I've got spare diodes for attempt 2.

The big electrolytics all look good, and I've felt all round them - no lumps or bumps.  I wouldn't have the first idea how to test them anyway. 

Do I need to use your suggested light-bulb technique?  I haven't got smoke, there's no smell of burning anywhere and the major symptom is a blown fuse.   The fuses come in packets of 10 and I've got 9 left!

But it's all on hold for today - I'm trying to work out how to remove the headlamp unit from a Peugeot 205 - all the wiring seems to have fallen off the back and it's completely inaccessible because of the fuse box bracket.  And it's freezing and drizzling out there.  And the local garage aren't answering the phone.

Faithful DMM on a lowish Ohms range.  Connect red lead to positive and black lead to negative (probably best to short capacitor to make sure it's discharged first).  DMM reading should start low and whizz up to very high Ohms or overload.  A lot of old analogue MMs put positive out on the black lead and vice versa but at that low voltage it probably wouldn't hurt a big fat cap like that.  If it sits at a steady low resistance reading then it's kapputt.

Agreed, but unless the capacitor is isolated from the rest of the circuitry you will get misleading results. Disconnecting the wire(s) from one terminal on the cap will be ok to give access to both terminals for this test to be of the capacitor only - which is whats needed. You can resolder it back on afterwards.

HTH

[jereboam]

OK.  I've removed 2 diodes, a section of PCB track and a chunk of my index finger.

Only one of the diodes survived.  When I said at the start that the boards looked like they had been soldered by hand, I think I may have been absolutely spot on.  All the component leads have been passed through the board and bent over before the solder has been applied.  They are an absolute pain to remove.  Years ago, I replaced my chisel shaped soldering iron with a more delicate pointed one.  It's absolutely useless for this sort of job - it takes forever to transfer enough heat to melt the solder boulders holding the components in place. 

And to make it worse, I can't find my thin-nosed pliers.  I have 3 pairs.  They've all gone.  I had to go next door and borrow some from my neighbour.  I'll have to do a small re-equip when I go to  Maplins tomorrow.   And heaven knows where the solder sucker has gone.  Found the box and the spare nozzle, but the tool iself has gone awol. 

And all the bl**dy lights just went out...

Back soon.

[jereboam]

Lights on again.  It was the new bulb I put in the light fitting in the hall last week.  Wife complained it was too bright, but it was exactly the same bulb as the other two in the fitting.

So, as I was saying before I was so rudely interrupted, the two dud diodes are out.  One has "IR5A" on it and the other "IR5B".  Do these numbers signify anything to anyone?  Google reveals nothing.

Do I still replace them with 1N502s?

[Chris_H]

OK.  I've removed 2 diodes, a section of PCB track and a chunk of my index finger.

Only one of the diodes survived.  When I said at the start that the boards looked like they had been soldered by hand, I think I may have been absolutely spot on.  All the component leads have been passed through the board and bent over before the solder has been applied.  They are an absolute pain to remove.  Years ago, I replaced my chisel shaped soldering iron with a more delicate pointed one.  It's absolutely useless for this sort of job - it takes forever to transfer enough heat to melt the solder boulders holding the components in place. 

And to make it worse, I can't find my thin-nosed pliers.  I have 3 pairs.  They've all gone.  I had to go next door and borrow some from my neighbour.  I'll have to do a small re-equip when I go to  Maplins tomorrow.   And heaven knows where the solder sucker has gone.  Found the box and the spare nozzle, but the tool iself has gone awol. 

And all the bl**dy lights just went out...

Back soon.

That was how I was taught to mount components for flow soldering before automatic insertion machines came along!

If you know a component is duff then cut the lead on the non-solder side and the remnant will fall out when you melt the solder.

What voltage is printed on the fattest capacitor in the middle of the board? [edit](Have found out by Googling that it is 2200uF 50V so you shouldn't need wonder-diodes)  BTW the IRxA/B are probably circuit references on the board? not component part no.[/edit]

[Andy B]

I'm impressed with this thread.
Help and advise on electrickery repair & diagnosis from afar!