{"id":319,"date":"2018-12-14T23:30:11","date_gmt":"2018-12-14T13:30:11","guid":{"rendered":"https:\/\/blog.hegars.com\/?p=319"},"modified":"2020-08-08T22:12:34","modified_gmt":"2020-08-08T12:12:34","slug":"roland-p-55-and-sc-55-partnership","status":"publish","type":"post","link":"https:\/\/blog.hegars.com\/?p=319","title":{"rendered":"Roland P-55 repair and its relationship to the SC-55"},"content":{"rendered":"\n

I acquired a P-55 from ebay that wasn’t working, <\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

Problem: No power to P-55<\/h2>\n\n\n\n

There was a dead short across the power pin (after blowing the transformer a few time before putting a meter across it) These Roland devices have reversed Negative Collar power inputs so its easy to blow if you just plug what ever supply you have laying around.<\/p>\n\n\n\n

\"\"
BZZZRT…..<\/figcaption><\/figure>\n\n\n\n
\"\"
Replaced Fuse. AC250V T3.15A, Nice and basic full bridge rectifier setup<\/figcaption><\/figure>\n\n\n\n

L78MR05 Linear Regulator with reset generator, removed and tested , I acquired some “new” ones from a spurious supplier and i wasn’t keen on using it, luckily the original one tested fine once removed from the board.

The 78MR05 is a 7805 with a circuit to hold a reset line active high\/low until the power line is stable that is fed to the uC.<\/p>\n\n\n\n

\"\"
My fear that the L78MR05 was DOA<\/figcaption><\/figure>\n\n\n\n
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Power section removed and cleaned <\/figcaption><\/figure>\n\n\n\n
\"\"<\/figure>\n\n\n\n

<\/p>\n\n\n\n

FAULT<\/p>\n\n\n\n

Input diode D1 turned out to be blown causing the short circuit, D1 is the first device inline to the power input. This is probably due to blown from a mispolarity.

I replaced D1 with a 1N4007 (700V RMS reverse) total over kill but I need to use a lesser diode like a 1N4001 (35V RMS reverse) this is all I had on hand at the time I will have to replace at a later date with a more appropriate diode. The original D1 looks like some sort of zener, there were no identifying marks.<\/p>\n\n\n\n

D1 turns out to be a 1SR35-100 silicon rectifier diode
<\/p>\n\n\n\n

\"\"
All back into the right spots<\/figcaption><\/figure>\n\n\n\n
\"\"
Its Alive!!!
<\/figcaption><\/figure>\n\n\n\n

How does it sound?<\/h2>\n\n\n\n

the Patches that the P-55 supports sound so much better that the equivalent patch on the SC-55<\/p>\n\n\n\n

The SC-55 relationship to the P-55<\/h2>\n\n\n\n

When the P-55 is connected to the SC-55 via the MIDI THRU port and the appropriate settings are input to mute the SC-55 Patches, the P-55 takes over the piano patches of the SC-55 giving a higher quality result.<\/p>\n\n\n\n

\"\"
`<\/figcaption><\/figure>\n\n\n\n

SNR Issues<\/h2>\n\n\n\n

issues of sound quality, work in progress<\/p>\n\n\n\n

Mask Rom <\/h2>\n\n\n\n

Wave ROMS<\/h3>\n\n\n\n

SHARP LH537<\/p>\n\n\n\n

https:\/\/snescentral.com\/chips.php?chiptype=MASKROM<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

I acquired a P-55 from ebay that wasn’t working, Problem: No power to P-55 There was a dead short across the power pin (after blowing the transformer a few time before putting a meter across it) These Roland devices have reversed Negative Collar power inputs so its easy to blow if you just plug what […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"site-container-style":"default","site-container-layout":"default","site-sidebar-layout":"default","disable-article-header":"default","disable-site-header":"default","disable-site-footer":"default","disable-content-area-spacing":"default","footnotes":""},"categories":[1],"tags":[],"_links":{"self":[{"href":"https:\/\/blog.hegars.com\/index.php?rest_route=\/wp\/v2\/posts\/319"}],"collection":[{"href":"https:\/\/blog.hegars.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blog.hegars.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blog.hegars.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/blog.hegars.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=319"}],"version-history":[{"count":28,"href":"https:\/\/blog.hegars.com\/index.php?rest_route=\/wp\/v2\/posts\/319\/revisions"}],"predecessor-version":[{"id":1294,"href":"https:\/\/blog.hegars.com\/index.php?rest_route=\/wp\/v2\/posts\/319\/revisions\/1294"}],"wp:attachment":[{"href":"https:\/\/blog.hegars.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=319"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blog.hegars.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=319"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blog.hegars.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=319"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}