Clarion APA Series Amplifiers
Clarion produced the APA line of car stereo amplifiers for many years. They are actually quite nice units, with good sound. There was a collaboration with McIntosh for some of the electronics, which gives it a nice leg up in audio quality. All of these amplifiers seem to suffer from similar issues, but at least they all use similar parts. I was unable to find any schematics or technical information on these amplifiers other than how to install them, so the troubleshooting is a bit rudimentary.
The ground planes involved on these boards are absolute units and you will need both a strong (80+ W) soldering iron and a hot air gun to really be able to sufficiently work on these boards. Recommended is also a power supply that provide 12 V DC at up to 5 A.
All work done here has been done on the APA 4200G and the APA 4400G, but from looking at old board pictures online, it seems many in the same family share a lot of characteristics, designs, and components.
Common Issues[edit | edit source]
- Doesn't turn on.
Doesn't turn on[edit | edit source]
There are a few things that this could be. First off: Check the damn fuse. The second thing to check is to see if the two power input terminals are shorted (i.e. 12 V and GND are shorted). If this is the case, then it's likely one of the filter caps on the inside died. These are humongous capacitors (10000 μF), and hard to find a replacement for. This thing runs hot, so it makes sense to see the filter caps dry out and die, but it also means you should take some serious care in selecting a replacement part. Because of the huge ground planes, it's really a headache to pull parts so it's recommended to just head up one leg of the cap and try to pull it clear of the via. That way, you don't have to remove the whole component but you can still effectively remove it from the circuit.
If you find that there is not a short between the supplies, but the amp is still dragging the supplies, it's likely an issue with the input stage of the power supply. From the input terminals, the power is filtered with a few large capacitors and then gated into the rest of the amp through a series of NDP6060 MOSFETs. The APA4200G uses four of these and the APA4400G uses six. There seems to be two root issues at play with this part of the circuit.
- Something happens (old age, thermal shock, overcurrent, etc) and one of the MOSFETs fails. As all the MOSFETs are in parallel to balance the load, this causes more load to fall onto the others, driving them to become worn out and fail quicker.
- The additional heat (These are heavily heatsinked parts) causes the plastic isolator rings on the screws holding the MOSFETs to the heatsink melts, causing the tab of the chip (12 V) to short to the heatsink, which is chassis ground (0 V).
So, it's a two-part failure. The best way to isolate what is happening here is to measure between drain and source on the MOSFETs with your meter from the underside of the board Make sure you're on the power supply side of the board and not the output amp side (just the side closest to where you would hook up the power connections). You should measure something like 0.1–2 Ω if this really is the failure mechanism you're seeing on your board. Then, just remove the screws from the MOSFETs that hold it to the heatsink an check the resistance again. If you still have a short, then you have a few bad ICs. They are all connected in parallel so I think you will have a hard time finding out which ones are broken if there is not any obvious failure. It's best to just remove them all and probe them out of circuit, and keep the good ones.
If you find that the short goes away when you remove the heatsink screws, this means that the plastic isolators have failed and either broke or became conductive (dielectric breakdown). This is actually not the worst case scenario and can easily be remedied. Just use some thin (not the good stuff!!) heatshrink around the head and the top 1–2 mm of the screw to create a DIY isolator. Make sure that the rubber is cooled down and doesn't catch on the hole in the MOSFET when reinserting it, otherwise you'll just get a short again.
Removing the NDP6060s[edit | edit source]
These chips are difficult to remove. A way to remove them is:
- Remove the screw holding the chip to the heatsink.
- Grab the tab of the IC with some pliers.
- Use hot air on the non-component side of the board directly over the through holes for the MOSFET, and continually exert pulling force from the other side.
- Clean the holes with solder braid. Make sure you do a good job, it is very difficult to reinsert the new chips if all the through holes are not perfectly cleared.
Typical Operating Conditions[edit | edit source]
When everything is working as it should, it was found that the 4200G pulls about 1.2 A at standby with no signal (any gain) and about 1.5 A with signal at 1.2 V gain. The 4400G pulls about 1.8 A idle and 2 A at 1.2 V gain with signal. Both of them pull ≈5 A from cold start for just a few milliseconds, but if your supply can't provide this, the amp will not start.