Kenwood KA-4040R - faulty channel (fixed)

Almost exactly 10 years ago I picked up this Kenwood KA-4040R Amplifier.

I'd put a "Wanted" ad on our local Freecycle page - I fancied a go at fixing a broken amplifier - so I specifically asked for something that was broken. So, this amp was given to me along with the CD player and Tuner (all separates). The fault on the amp was that one channel was not working. At this stage I knew nothing at all about how amps work (and pretty much still don't), but I set to work with the only relevant tools that I had - a multi-meter and an ESR meter for checking capacitors. Within a short while I had found what I thought was a dead capacitor. Having de-soldered it and checked it again, it seemed to be fine. So I reinstalled it and the amp worked! Easy fix, and the amp ran fine for the next ten years, right up until a couple of weeks ago. The left channel started playing up again. This coincided with a lot of scratchy interference when adjusting the volume, and a quiet "thudding" sound on the left channel. This thudding was louder on certain inputs (CD, Tuner, Aux, Phono), but not really noticeable on the second tape input. As I was mulling this over something in the amp went "pop". I unplugged it all and removed the cover. This is what I saw:

This is a 3300uf 6.3v capacitor on the "EQ" board which has spilled its guts into the amp.

I bought a couple of replacements and fitted them but I was not hopeful that this, and cleaning up all the cap juice, would sort the issue.

I was right - with the new caps fitted there was clearly some sort of current leak as there was a very rapid thudding on all inputs and within about 30 seconds of switch-on the speaker protection relay fired. On a positive note, the left channel did now have audio, albeit quiet and drowned out by the thudding. I did some more checks. I found that about half of the diodes which appear to serve the input connections had fried. So I replaced them, along with some transistors that I'd had a hunch about.

The original diodes are no longer available but the consensus on the internet was that IN4148 diodes would serve as a suitable replacement. I managed to find some new-old stock transistors so replaced like-for-like.

And whilst I had it in bits, I took the front panel apart and cleaned all the pots with some Super 10.

So, 28 diodes (I replaced them all...) and four transistors later, and a liberal dose of switch cleaner, I now have a fully functioning amplifier again. Cost - less than £10 to fix. I am extremely pleased ;) But I am now toying with replacing all the caps in the amp - they are 27 years old and are unlikely to be in the best of shape. I like the amp and it would be a shame if it got wrecked by a failing cap.


More soon, no doubt...


D.

Hammer time...

Just a quick one. Today is Father's Day and this was the gift from my boy.

Love it!

More soon, no doubt....

D.

Nitecore D4 charger fault (fixed)

I bought this Nitecore D4 charger from Fasttech nearly four years ago. I use it for charging my collection of Samsung 18650 batteries. I use it everyday.

In the past few days though my charger has been misbehaving. It doesn't appear to have been charging properly, especially when loaded with cells. The screen was also flickering and the information on the display was random nonsense. Oh dear...

Naturally, I had to open it up. This is the charger with the back removed:

Nothing out of place there, although I note some heat damage around the diode #10 (on the left of the picture). I thought I'd better lift the PCB out. Since I wasn't sure whether I could lift it out with the battery holders attached, I desoldered the four springs and earth wires, and decoupled them. I then removed the three screws from the bottom edge of the board and gently teased the board out. On the way, and as soon as I could get my fingers in the gap, I disconnected the power for the screen LED. This is what I saw next:

Yep, a faulty capacitor on the power supply side. I decided (and hoped) that that was likely to be the cause of the problem. I desoldered the faulty cap. It's a 1000uf 16v. I cannot tell what brand it is:

I had a look through my box of electronic goodies and found this, which I think is a Panasonic:

So I soldered it in....

And then I re-assembled. This was a bit of a faff, really. The LED screen sits in a plastic holder. The plastic holder sits loose in the case but if it's not in exactly the right place, the screen display will not work. I found this out only after my first attempt at reassembly. Indeed, getting the screen in the right place so that it would work took longer than the actual repair. Anyway, here it is back together. I've resoldered the springs and earth wires:

And here is my Nitecore  D4 working well again:

Happy days!

Here's a link to Fasttech in case you want to buy one: Nitecore.

More soon, no doubt....



D

ESP DVR-EZ - "no HDD" error

A friend asked me to take a look at this DVR which she has in her shop and which is supposed to record the images from four cameras that are dotted about the place. The problem was that it wasn't recording anything. Once I'd hooked it up to a monitor, I could see a message on the screen - "no HDD". Since there was no suggestion that the HDD had been removed, I disconnected all the cables and opened the DVR up. There was indeed a HDD in there but rather than wondering whether there was a fault with that, I could immediately see blown capacitors on the power supply for the HDD. Here are some photos of the DVR and internals:

And here are the two blown capacitors:

The values are 1000uf 16v. The smaller capacitors (470uf 25v) situated nearby were fine. So, I replaced the faulty caps with some new ones from CPC. Here they are:

Before reassembling everything I also checked the state of the HDD. It worked fine despite its age, although to test it at all I had to dig out an old IDE to USB connector. Yes, remember IDE HDDs?

I'll update this post once I've been able to check whether the new caps have resolved the issue. And for my own benefit, here is the relevant user manual for the DVR.

More soon, no doubt....


D

LG 32LD490: dead then alive

Seems like a while since I last put a post up on here. Over the past few years I've posted something about my Mondeo when sorting it ready for its MOT each October. Unfortunately, over the past 12 months the rot had got the better of it and it fatally failed its last MOT. It's now scrapped and has been replaced with a Mk7.5 Fiesta ST Line. I've got some plans for that next Spring and no doubt will be making some posts on here about that.

Anyway, on to tonight's project. I was asked to look at this LG TV.

I'm not sure how old it is but when powered up presented with a solid red stand-by light. The TV was otherwise dead, though, and could not be switched on. First thoughts were the caps on the power board but they all looked OK. The ones I could get to with my ESR meter were fine. I also checked the diodes on the power board which were all good. Finally, appropriate voltages were present at the connection to the main board.

I therefore turned my attention to the main board, in particular the BGA chips. In this TV, the two chips both have fairly large heatsinks so I wondered whether a little hot air reflow might help things.

In order to do that I had to remove the heatsinks which were on with sticky tape and hot-melt glue. The heatsinks came off easily enough with some warm air blown over them. I then ran some liquid flux under each chip and warmed them both to 200c for about five minutes.

Before refitting the heatsinks I checked whether the TV worked. On pressing the "on" button I could see that the LED backlight was now working and the standby light was now blue.

That was good enough for me. I cleaned the sticky tape from the back of the heatsinks and refitted them. Instead of more sticky tape I used some proper thermal paste and more hot glue to hold them in place.

And the TV now works. It's been on for a couple of hours playing some recorded TV programmes from a USB stick. Sorted ;)

More soon, no doubt....

D