{"id":1749,"date":"2014-10-21T20:20:39","date_gmt":"2014-10-21T20:20:39","guid":{"rendered":"http:\/\/www.richardmudhar.com\/?p=1749"},"modified":"2014-10-21T20:21:35","modified_gmt":"2014-10-21T20:21:35","slug":"fixing-a-maplin-eap450-car-amplifier","status":"publish","type":"post","link":"https:\/\/www.richardmudhar.com\/blog\/2014\/10\/fixing-a-maplin-eap450-car-amplifier\/","title":{"rendered":"Fixing a Maplin EAP450 Car amplifier"},"content":{"rendered":"

This amplifier is used for parties at The Oak Tree<\/a> where we have no power on site – a 12V leisure battery is good for about 7 hours. I\u2019d noticed one of the pots getting scratchy so one of the four channels was low. This is a four-channel amplifier, and I use it bridged 2×2 as my speakers are 8 ohm. The amp works but I\u2019m losing power, experience tells me this sort of fault doesn\u2019t fix itself.<\/p>\n

The go-to site for car audio tech is Basic Car Audio Electronics<\/a> so if you\u2019ve blown your amplifier and are looking to fix it then that\u2019s a good place to start. The tl;dr version is it\u2019s probably not worth your while, get a new one. The trouble with blowing the amp is not only do you have to find and change the blown part, but also establish the rest of the parts are okay. I\u2019m just fixing a passive part in an otherwise normally functioning amplifier. It\u2019s probably still not worth my time but it\u2019s criminal to junk the amp for the sake of \u00a32 worth of parts.<\/p>\n

I did get a meter on one section of the pot and established that it is intermittent and ratty. So I didn\u2019t need the schematic. It\u2019s nice to have, though, but knowing Maplin I figure it\u2019s probably not worth calling them up and asking them to send a PDF or a dead-tree version through the post. I\u2019m still sore about the way they washed their hands of a portable TV that failed after 15 months. On investigation it has clearly not worked right and been incompetently hand-repaired at the factory leading to the screen failure.<\/p>\n

Inspection of the circuit board and a bit of Googling turns up some leads. I observe the circuit board is marked APA-450 Rev 2 and Googling APA-450 tells me that Clarion used to make one of these<\/a>, and the control panel looks suspiciously similar. So now I know what a Maplin EAP450 is – presumably they bought the rights to rebadge this discontinued Clarion amp in a different housing. Or perhaps there\u2019s some noname Chinese company in Shenzhen hawking their production line to whoever will pay \ud83d\ude42<\/p>\n

I got the service manual and schematic from those nice guys at Elektrotanya<\/a> and established that the part numbers tally with the board.<\/p>\n

plan A – changing the pot<\/h2>\n

Ebay was my friend in sourcing the pot, as it happens also from China. One of the great things about Ebay is the variety – it\u2019s important to get the length of the splined shaft right so it doesn\u2019t stick out too far and this is a slightly oddball length. A 6mm spline shaft is close enough.<\/p>\n

\"Pots
Pots showing different pitch<\/figcaption><\/figure>\n

 <\/p>\n

I got that right, but I was caught out by the pitch of the pins being smaller than normal. I\u2019d already dismantled the amp before I spotted that. D\u2019oh.<\/p>\n

Take a photo before you dismantle the amp<\/h3>\n

You can\u2019t have too many decent photos of the gear before<\/em> you take it apart . Once I had taken out the screws I got to see the PCB – it\u2019s clearly not the finest reflow job I\u2019ve ever seen<\/p>\n

\"Maplin<\/a>
Maplin EAP-450 circuit board<\/figcaption><\/figure>\n

 <\/p>\n

plan B – fix the original pot<\/h2>\n

Time for Plan B – dismantle the offending wafer of the pot.<\/p>\n

 <\/p>\n

\"Closeup<\/a>
Closeup of wafer<\/figcaption><\/figure>\n

By carefully bending the tabs I could get the wafer out and look for the problem – there\u2019s a faint patch of shiny something not right at the top left of this, which I cleaned off with some isopropyl alcohol. Plan C was going to be replace this pot and the other one with two fixed resistors per wafer. There\u2019s no real need for this sort of control on a power amp. Ideally I want to line the amp up for full-scale output at +4dBu – there\u2019s far too much gain and it needs pulling well back. the line level input sensitivity is specified as 200mV to 6V<\/p>\n

final test – success<\/h2>\n

 <\/p>\n

\"output<\/a>
output at full scale<\/figcaption><\/figure>\n

This is the amplifier at just over 40V p-p showing the two bridge amplifier outputs which are out of phase (I am too cheap to get the probes to set the read out right, so it shows 1\/10 of the real sensitivity)<\/p>\n

\"clipping<\/a>
clipping simultaneously<\/figcaption><\/figure>\n

 <\/p>\n

and the final trace shows both bridged sides going into clipping at the same time.<\/p>\n","protected":false},"excerpt":{"rendered":"

This amplifier is used for parties at The Oak Tree where we have no power on site – a 12V leisure battery is good for about 7 hours. I\u2019d noticed one of the pots getting scratchy so one of the four channels was low. This is a four-channel amplifier, and I use it bridged 2×2 … Continue reading “Fixing a Maplin EAP450 Car amplifier”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":1755,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[57],"tags":[277,276,278],"class_list":["post-1749","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-electronics","tag-eap450","tag-maplin","tag-repair"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"https:\/\/i0.wp.com\/www.richardmudhar.com\/blog\/wp-content\/uploads\/2014\/10\/1407_eap-board_P7170144.jpg?fit=640%2C480&ssl=1","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p5aOO7-sd","jetpack_likes_enabled":true,"_links":{"self":[{"href":"https:\/\/www.richardmudhar.com\/blog\/wp-json\/wp\/v2\/posts\/1749","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.richardmudhar.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.richardmudhar.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.richardmudhar.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.richardmudhar.com\/blog\/wp-json\/wp\/v2\/comments?post=1749"}],"version-history":[{"count":2,"href":"https:\/\/www.richardmudhar.com\/blog\/wp-json\/wp\/v2\/posts\/1749\/revisions"}],"predecessor-version":[{"id":1757,"href":"https:\/\/www.richardmudhar.com\/blog\/wp-json\/wp\/v2\/posts\/1749\/revisions\/1757"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.richardmudhar.com\/blog\/wp-json\/wp\/v2\/media\/1755"}],"wp:attachment":[{"href":"https:\/\/www.richardmudhar.com\/blog\/wp-json\/wp\/v2\/media?parent=1749"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.richardmudhar.com\/blog\/wp-json\/wp\/v2\/categories?post=1749"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.richardmudhar.com\/blog\/wp-json\/wp\/v2\/tags?post=1749"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}