Radios - Troubleshooting and Repair

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WRDendy
Can tell where the 480 was built
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Radios - Troubleshooting and Repair

Post by WRDendy » Tue Nov 01, 2022 4:51 pm

This is more of a blog post than a structured how-to manual, but nonetheless I hope that you will find it interesting, and with luck it might serve as a helpful staring point for others with radio problems in the future.

A few weeks ago DCWalker handed me a cardboard box containing a radio that he couldn't get up and running in a car - I think he may have said that he had got as far as getting the security LED to light up but no further, but the first rule of fault finding is to forget any prior information, lest it send you down the wrong path! To use a car analogy, a customer comes in complaining that every time they turn left onto their driveway they get a clunking sound, and they think it's definitely something to do with the steering. You then spend half a day pulling the rack apart to no avail, before someone comes over and points out that one of the drop links is loose.

Anyway, here's what was in the box:

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It's a Volvo VC963, which, as with many Volvo radios of the time, is a re-branded Philips model, specifically a DC632. Not a huge amount of information about either models online, and at this point I decided not to spend any time looking for schematics or other details until I had an idea about what I was dealing with.

I made up a test harness allowing me to supply 12V to the permanent and switched power lines (as well as a ground connection), and speakers to the front two channels, but before turning it on I decided to have a quick look inside just to check if there was anything obviously wrong, or that might be damaged by applying power (and yes, I'd checked the fuse by this point :D ).

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Yep, that's definitely a radio alright. But what's that brown stain on the board under the heatsink? Enhance!

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Ok, here's problem number one. Looks like two big capacitors have leaked electrolyte everywhere. This isn't to say the whole thing wouldn't work, it really depends what they are there for (in this case I think they're on the input, judging from my tracing of the circuit), but they might cause things to behave strangely, which would confuse any other troubleshooting efforts. Also aside from anything else, the electrolyte is corrosive and could be causing damage to the traces on the board under the spill.

This, by the way, is a problem that I suspect a lot of older radios either already have (although they may still work), or will have in the future. Electrolytic capacitors have a finite lifespan, capacitors from the late 90s and early 2000s particularly so (see also: Capacitor Plague).

With all that said, better to change them immediately before proceeding any further. Flipping the radio over reveals this on the bottom:

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And that's just a corner. Lots of things going on. Plenty to go wrong. After some poking and measuring I determined that these were the things to desolder:

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Note the SMD cap soldered between the legs of the lower through-hole cap. At first I thought this was a re-work, but after removing it I could see pads for it. It's almost definitely fine and doesn't have any polarity so I just put it to one side for re-use.

I removed the solder using plenty of flux and some wick, then pulled the caps out from the top:

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Actually not too bad, although there's some corrosion on the leg of the diode half way up, and the traces under the ooze are a bit unknown.

Here are the capacitors:

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Black ones are originals, blue ones are replacements. The originals are Nichicons, so clearly this comes from an era when manufacturers cared about the quality of their products. That was a long time ago. Matching caps for replacement is fairly easy - same (or very similar) capacitance (in this case 2200uf), and the same or greater voltage rating. I happened to have an exact match so in they went:

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Haven't cleaned up the spillage on the board yet

And back on underneath:

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Spot the new solder vs the old.

Had a go at cleaning the old electrolyte off the board using various combinations of isopropyl alcohol, contact cleaner and flux cleaner, agitating it with a fibreglass pencil. Here's an in-progress shot:

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I didn't go much further than that. As you can see, the traces are all fine (I suspect it's a coated board) and I was worried about causing further damage. As an aside those black diodes caught me out - I thought they were Schottkys and I couldn't buzz them through, so I assumed they were damaged and removed them. Turned out that they were axial rectifiers and I had the meter set wrong, so back in they went!

At this point I decided to apply some power and see what happened. Could it be that two blown power caps were all that was wrong with this thing? Of course not! :lol: With power connected the radio still wouldn't respond to the power button, although the security LED was blinking intermittently and irregularly. Could it be that those two caps were bad then the others were on their way out as well? Might as well replace them all just in case!

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That's better - all the blue caps are new ones (same rules apply, i.e. same capacitance but some of the replacements have higher voltage ratings. Think of it as an upgrade :D ). There's one original black one in there that I didn't have a spare on hand for, but I desoldered and removed it, tested it (it was fine), and re-fitted it. Much easier to do that than to test it in-circuit. There was also a mystery ceramic (I think) cap (right in the middle in the picture above) which I couldn't identify, so again I did the remove, test and re-fit routine. Here's a picture of it removed if anyone has any ideas:

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Anyway, with a full complement of new capacitors I still couldn't get it to switch on, but at least I had eliminated them as problems, and probably significantly extended the lifespan of the radio by fitting new ones.

At this point I decided to make sure that the power button was actually doing something. The front panel has various connections onto the main board, but it didn't take long to identify the right connector and the right pins by poking around with a multimeter:

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Once I'd found them I got a pin on that connector being pulled to ground every time I pushed the power button, so I could safely assume that it was working (or at least doing something). I thought it would be worth checking the removable panel on the front as well:

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It occurred to me that there might be more to this than meets the eye, after all the radio could be absolutely fine, but if this doesn't work then it will never turn on, much like a car that's absolutely fine but immobilized. Two screws later:

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...and that's all there is. Just some LEDs, switches and some pogo pins. No exciting cryptographic ICs, nothing at all. Presumably the security extends to it being there or it not being there, so any buttons would work on any radio. Not very interesting for us, but I suppose it only had to be a vague deterrent to persuade the yobbo to break the window of the next car down instead of yours. In any case, clearly not the problem we're looking for.

I still had the radio connected to power, and I noticed that the intermittent-ness of the security LED seemed to vary as I moved it around the bench to make space for things. This made me suspicious - could it be that there was a loose connection or a dry joint somewhere? I started going over the board in detail and sure enough some of the solder joints looked a bit off. I assume if you've made it this far through without getting bored then you've probably also read my speedo repair guide, which covers dry joints. These were similar, but most of the joints in question were about a quarter of the size of the joints on the cluster, so it really was a case of going over every single joint just in case, as I really couldn't tell which were good and which were not in some cases:

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Above you can see a few of the worst ones. I haven't highlighted them on purpose, see how many you can spot!

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Adding plenty of flux is key to making life easy here. This is an old board with old solder, and the flux really helps to cut through the impurities and get the joint flowing nicely.

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Above we see even more carnage - bare in mind that there is some magnification going on here, but to anyone who's repaired an instrument cluster this will probably be a familiar sight.

Finally I turned my attention to the various ICs. These would have been done by a pick and place machine and a wave oven (probably) so had very little solder on the joints. We're talking millimetre-if-you're-lucky gaps between terminals here, so the technique is to drench the whole area with flux:

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Then make sure the iron is clean, add a very small amount of solder, and then 'drag' across the legs to re-flow the joints. Not as hard as it sounds, but I'd suggest practicing on something else that's really broken first if you haven't done much SMD rework before:

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Finally, cover the whole work area in isopropyl alcohol or flux cleaner:

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And clean up with a brush (get an ESD-safe one for bonus points. I am at least doing this on an ESD mat!):

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Most flux is at least slightly corrosive (even if it claims to be 'no-clean'), so it's worth getting it all off if you want the thing in question to last.

All that done I re-connected the power, and...

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Success!! It powered on and off reliably, and recieved radio nicely. Whether or not it would have worked if I hadn't replaced the caps we will never know, but I can say that it will carry on working for a lot longer with the new caps installed.

Since I had the radio open I thought I might as well check the tape mechanism.

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It made noise but there was definitely some wow and flutter going on with the test tape, and insertion and ejection was a bit lethargic. Four screws and two cables liberated the mechanism from the chassis:

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And four more screws on the underside of the mech...

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...Revealed the belt:

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Much like any other rubber, tape belts wear out and should be replaced. Luckily this one wasn't too bad as I didn't have a spare, but I did lubricate all the moving parts and springs whilst it was open.

Whilst access is available it's also worth cleaning the playback head:

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Once again some isopropyl alcohol and something to wipe it off does the trick:

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Re-fitting is then of course the opposite of removal, although now is a good time to consider the much less cluttered top side of the board whilst the tape mech is out:

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It's beyond the scope of this post, but down there are all the things we would want to play with were we to decide to add an aux-in or bluetooth option to this radio...

Finally, with the whole thing re-assembled, working, but with the covers off, let's see if we can work out why it failed. Switch to thermal vision!

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Bottom on the left, top on the right. After being on for just a couple of minutes it's starting to get quite hot, and no surprises that the hottest areas corresponded exactly with where I found the most dry joints and failed components. On the top we can see the heatsink very effectively moving the heat up and away from the amp chips and creating an oven for the power caps, and underneath we can see the ICs glowing away nicely. Shame that it had to be working to get those pictures as it would have saved quite a lot of time, but nice to see what's going on anyway!

Whilst the heat was probably a major contributing factor to the failure of the radio, I wouldn't classify it as a bad design. The temperatures are all well within spec for the components on the board, and I'd imagine that no-one expected it to still be in use a quarter of a century later. Of course the temperatures are nowhere near high enough to melt solder, but the repeated heating and cooling (imagine driving home on a winter's night, phat beatz pumping, then turning off and letting it go from 60+ degrees to zero or below, repeatedly, for decades) would be enough for joints to go dry, components work themselves loose, and capacitors to loose their guts everywhere. Similar story to the instrument cluster really, and as I said further up something that I suspect will start happening more as the electronic items in these cars continue to age. Much like everything else on a 480 though, nothing that can't be fixed, within reason.

Anyway, thanks for reading along, and let's hope this radio continues to give many more years of high-quality auditory service!

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Last edited by WRDendy on Tue Nov 01, 2022 5:22 pm, edited 1 time in total.
Formerly known as 'Jaster'
Current: '94 GT & '88 ES
Former: '89 ES

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dcwalker
480 Is my middle name
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Joined: Sun Sep 16, 2012 12:30 pm
Location: York

Re: Radios - Troubleshooting and Repair

Post by dcwalker » Tue Nov 01, 2022 5:19 pm

Will, that is a very interesting read with which I just about kept up - instrument cluster re-soldering I can and have successfully done many times now, but I wouldn't know where to start on there. Which is why, of course, I passed it to you :lol:

It's clearly been a labour of love, and I really do appreciate your efforts with it. It'll probably outlive the 460 it comes out of now!

David
Current: 1994 480 GT, 1996 460 CD & 1997 440 LE with lots of optional extras
Previous: Celebration 331 (re-homed with Richard S), Celebration 467 (returned to Martin Mc); Celebration 346 (re-homed with Alan480); Celebration 269 (scrapped abandoned project), Celebration 73 (sold on after 6 years), 1992 ES, 1988 ES - and numerous other non-480 Volvos!

jifflemon
480 Is my middle name
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Re: Radios - Troubleshooting and Repair

Post by jifflemon » Tue Nov 01, 2022 8:33 pm

Absolutely bloody fascinating!

I love when people take the time to document stuff like this; I may never actually do it, but having something like this as a starting point would make it much less daunting.

10/10 will read again!

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MisterH
480 Is my middle name
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Joined: Sat Nov 24, 2018 6:15 pm
Location: Stockbridge

Re: Radios - Troubleshooting and Repair

Post by MisterH » Wed Nov 02, 2022 2:53 pm

I am a sucker for vintage audio - the only issue is that I have no idea how to go about maintaining stuff, so I just have to hope that I know people who can fix them, and that parts are available for my units. While I will probably refrain from prying open my rare Decks for now, I will definitely be referring to this at some point!
Current Jobs to do (23/1/22):
Fix Central Locking
Fix drivers side speaker
Annoying Scratching Squeak
Water leaks
Complete Front O/S rebuild

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Jay-Kay-Em
Can tell where the 480 was built
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Re: Radios - Troubleshooting and Repair

Post by Jay-Kay-Em » Fri Nov 04, 2022 7:34 pm

Amazing post and a great read.

It's quite inspiring and keeps me going that people invest the time, skill and knowledge into something that anyone else would throw away. Love that.

I'll also be fitting my dream 1997 Kenwood head unit (oneday!)
Jay-Kay-Em
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