That took a bit of finding, I wasn't sure which came first the 51 or 52. Anyway 1N5251B is a 22V 500mW zener diode, a pack of 5 for £1.50 that should last a while.
I'll email you a shopping list later.
Do we need a replacement for D93?
Please remove D87 and have a look at it if you think it's faulty.
We also need R91 and R93 is there anything else?
So you guessed right about D91, but glad we’ve been able to check.
D93 is OK , 6.7v and I. D87 gives a voltage both ways. However, I think it’s identical to D91 – I can see the 52, so will have a spare anyway. (I need to take a few days off, and avoid getting soldering kit out again, so a good time to do it would be while waiting for components to arrive.)
My only thoughts are C93 next to the burnt out resistors and C88 across the board, next to D87, which was bent over. Are these caps? If so C88 passes the increasing resistance test. C93 registers a resistance for a split second then goes straight to OL. If you think there might be a problem I’d prefer to order a replacement now, even if it turns out to be a waste of money. It, and C88, are marked:
E
471
I’ve checked all the resistors and diodes and caps on the hot side of the board, but not the blue jobs near the mains supply, nor IC81 or PC41. I assumed that nothing would have got through to the cold side.
Ah, just noticed another brown two legged feller near PC41. It show OL. It’s markings are:
B, possibly with a + to the right of the B or just a black spot
102
Is there anything else I should check?
New components have been ordered, so there will be a delay of at least a few days. In fact, for one resistor, they're only promising delivery on April 10th.
New components have arrived, though looks too nice to be indoors, so maybe Monday before I get round to thing.
Stroker, do you want me to install everything, including IC91?
I agree it's way too nice to be indoors! I would recommend leaving IC91 out for the time being and replace everything else. Then power on with the mainboard disconnected and check the standby supplies, that is everything apart from the main 5V and 3V3. I'd do it this way just in case we have missed something and we have another incident although I think this is unlikely.
If all is ok fit IC91 but do not use the link on R95/98 anymore. I recently found that Q101 on the motherboard (next to the power connector where we found the fuses) is used to supply 5VS to the P/S connection on the power supply board, the collector and emitter of Q101 effectively connect 5VS to P/S so you should be able to short these together to turn on the main supplies. So I suggest you use a piece of solid wire to short 5VS and P/S in the connector on the PSU. Initially power on with the motherboard disconnected just in case.
You haven't said if you have received your high power (100W?) soldering iron yet. If/when you do I want you to touch up the joints on the 15 pin connector on the motherboard, use plenty of flux and add more solder if needed. Keep the iron on each joint long enough to get the solder to flow freely, I cannot emphasis this enough we need really good solid connections on here. Having said that do not go mad and leave the iron on way too long as you risk overheating the board, the low voltage pins like 5V and 3V3 will need more heat than the likes of FL- and FL+
If you are worried about this solder one or two joints and post a pic so I can see before you do the others. I am hoping that these bad joints are the real reason we cannot get the box to power up properly, bad power supplies to the motherboard circuitry may not be sufficient to be passed on to the front panel and prevent the display and switches from working.
OK, back to work Stroker! Monday promises to be a bit of a dull day. Actually, I didn’t order a 100w iron, but I did find my old one, so I do have two 30w ones and four bits. If you think 100w is essential for the connector on the motherboard I’ll get one. Or perhaps try with what I’ve got and take some pics. Another novice question, what is the technique? Do I apply some flux to the joint, melt it, then melt the solder and expect to see it fill the hole? Sorry – basic question!
I gave you quite a few things to do in the last post, I did this because I thought we may be too busy enjoying the weather to be posting messages. So I wasn't really expecting you to do it all on the same day.
I suggest you concentrate on the the PSU to begin with although if you find you have the time try soldering the FL+ and FL- end of the 15 pin connector on the main board. These I expect to not be so heavy as the 5V and 3V3 pins and so should be easier to solder and my thinking is that if the FL supplies are used on the display you may produce signs of life (this is probably just wishful thinking).
When you come to the 5V and 3V3 pins I am not sure how heavy the power tracks in the board will be. So don't expect these to heat up quickly when you apply the soldering iron, it may take 30 seconds or more before you see any sign of the solder melting. If the tracks are really heavy you may find that the iron cannot supply enough heat to raise the temperature enough, you will have to suck it and see.
I am not an expert at soldering but I remember being told by a soldering trainer that you should heat the joint first and apply solder once it has heated up. However in practice I tend to put a little fresh solder on the iron first then heat the joint and add more solder (if needed) when I see the old solder melting freely. Using flux should also help to spread the heat and in any case shouldn't do any harm.
I'll try to explain why a badly soldered joint is such a big deal on power supply connections. For example you have a 5V supply connected through a bad joint which adds 0.1 ohms into the supply path and the current along the path is 5A, there will be a voltage drop across the bad joint of 0.5V (ohms law V=I*R) so only 4.5V will arrive at the load. Most 5V devices only work reliably down to 4.75V so 4.5V is not enough for them to work properly.
did you recive my pm requesting which account you wanted deleting as ive had no reply
I'm sorry DCG but I have made no such request and have not received any pm from you. Do you have your wires crossed?
that wasn't directed at you m8
Some good news. We have the expected voltages at the output end of the PSU, albeit the +8v came in at 7.1v. +5VS is the normal 5.1V. As expected, no +5v nor +3VS and no P/S.
At R98 and R95, I’m getting 1.3v. On re-checking, I find I’m not getting reliable continuity between the cold end of R91 and the hot end of R98, so will try re-soldering that. I’m getting 113.6v/108v at either end of R91 and 403v/332c across R92 near the transformers. Is that OK? If you’re happy, shall I go ahead and fit IC91? Or do we need to get 22v to R98 (which is what we had before)?
I think we need the 22V for IC91 to work. Double check you have D91 the right way around and check the diode next to it is not shorted (was this replaced?). You should have continuity between R91 and R98 as you say - I think I need a pic of the underside of the board covering R98 to D91 and IC91. If you have a high voltage on R91 it could damage C92 - what voltage rating is C92? C92 could get very hot and even explode!!!!!!!!!!!!!!!!
IMG_5014.jpgIMG_5017.jpgIMG_4669.jpg
Actually I am getting continuity between R91 and R98, and I always checked for continuity between each pin I fitted (not the solder) and a distant point on the same track before trimming the pin. However this particular doesn’t always show up with continuity.
D91 and D93 are Ok, and D91 pointing same way as before. D93 was not replaced. Pic attached.
A pic of the underside in all its horror, together with approx the same area some weeks ago. The fact is I had a lot of problems getting solder hot enough to free the folded over part of the pin, and even to resolder yesterday. I’d get a small blob near the hole, but the next thing I knew I had a little ball bearing running around the boar – in fact just spotted a tiny one from the photo that I hadn’t cleared. I have a hotter iron on order and should be here in a day or two. I hope the damage is repairable.
C92 is 50v 22µF. So I’ve done something serious to let 100v get to it. I should have mentioned that there is no voltage at R93 next to R91. Could the two faults be connected?
Yes you are right it is a bit of a horror picture - the only option is to do some serious patching up. Please remove R91 and R93 clear solder from their holes and take another pic so I can formulate a plan - I am assuming you have more replacements for these resistors. I will probably need to show you the next step using a pic - I wonder if I will be able to post it?
Sorry, I forgot to say you should be sitting down with someone at hand with a cold sponge to mop your forehead before looking at my pics.
Looks like my new soldering iron arrives Thursday (from my normal electrical wholesaler). So, best wait until then to minimise further damage. And yes I have plenty of those resistors - ordered two of each before realsiing they came in packs of ten!
Thanks for, in the cir***stances, a measured response.
I would not have thought you would need a high power iron to work on the PSU board. I hope we can patch this up although it won't be pretty when we've finished. I am still hoping to see the box work but if was a cat it would be really short of lives by now. By the way the PSU board is only single sided (tracks on one side only and no internal ones) and does not have plated through holes and so solder will not be drawn into the holes. The cause of your difficult in soldering is due to damaged tracks and missing pads - nothing to solder to - the one leg of R91, for instance is surrounded by fibreglass and not copper.
I've got things to do tomorrow so do not expect quick replies.
IMG_5020.jpg
Pic attacheIMG_5020.jpgd.IMG_5020.jpg
Thanks I need to think about this.
I am beginning to think your soldering iron bit could be a problem - does solder stick to it? The first time you use a new bit you need to apply solder to it as it warms up so that you coat just the tip with solder this is very important otherwise you will struggle to solder with it. You need to keep the tip coated with solder at all times and remove excess solder and crap with a wet sponge (or just flick it off into a bin). If you have a spare bit perhaps it may be worth changing it. Modern bits are coated with iron and you are not meant to file them because you will remove the coating. If it is your only bit or if you are not worried about it's lifespan you can file the end down to the copper and then coat it with solder as it warms up. I will have to leave you to decide what's best.
Ah, that explains a few things. Yes, solder has been sticking to the tip. Will try the treatment before the next job. That’s assuming you think a repair can be done – fingers crossed.
Try this link - if I am allowed to post it - Moderators this is just a link to soldering tips.
_http://www.instructables.com/id/Soldering-101%3A-Lesson-1%3A-Tin-the-Tip/
Last edited by cosworth4x4; 19-04-2017 at 09:08 PM.
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