Technics EX35 Amp and Powersupply Replacement - Page 1
Forum section: electronics / projects

author: tbullock
author_rank: Newbie
timestamp: September 10, 2019, 06:06:29 am
content: Heyo,So first off I'm a new user to this forum as well as inexperienced with electronics and I wanted to share a project that I'm taking on with a group of nerds that might be able to give me useful feedback from time to time, hopefully some of you might find this interesting too. I own an older Technics digital organ, specifically the EX35 which was built in the early 90s. At some point over the last several years the organ became inaudible unless you pressed your ear closely to the speaker. So presumably something had died on the amplifier circuit, unfortunately just fixing whichever component was broken on this board is no longer really plausible.The Amp circuit board shares a PCB with the power supply for the organ and when I took the circuit board out for repair I managed to drop the PCB and break sizable chunk off, breaking completely through several traces and lifting others in the process.Unfortunately the machine is so far out of production nobody I can reach seems to be able to find parts for the machine so I'm kind of left with either repairing the PCB or potentially building a new amp/power supply from scratch. I've decided that building a new PCB and learning the requisite electronics skills is within scope for me so that's why I've decided to do. I'm not particularly concerned with parts or time cost here since this is being done strictly at the hobby level.So some more information.I do have a scan of the service manual of an equivalent machine (the EX25) which was a contemporary paired down variant of my organ. I've checked the schematic for the amplifier and it appears to be effectively identical to my existing circuit board (https://drive.google.com/open?id=1f77hB25Zf2Y-GpWfPzsY3qVCt8TnQD8V)So far I've decided to take the following plan with the replacement project:1. Redraw the amp/power supply circuit into modern CAD tool (I've chosen kicad)2. Make a part list for each component and check for either modern equivalents or if the older components are still being produced just use those3. Draw a new layout, keeping the existing physical foot print (due to mechanical constraints)- I plan on using through hole components for everything so that I can more easily re-assemble the final product myself4.5. Profit?currently I'm redrawing the schematic and learning some basics of kicadAnyway, that's my project, thoughts?

author: tbullock
author_rank: Newbie
timestamp: September 10, 2019, 10:26:04 am
content: I think the first thing that I could use help with is identifying some componentsFor starters the diodes comprising the 2 rectifier circuits and a few transistors- Diodes 1 and 2 are labeled with 0201 and on the schematic are identified as SVDGERA1502Y- Diodes 3 - 10 are labeled with SV304 and on the schematic are identified as SVDGS320-15 and MA165TA5, despite the different part numbers these have the same physical part on the circuit board.- Transistor 1-3, 5, 6 and 11 are all physically identified with 301 04G and identified as 2SC2320LFG on the schematicI've not been able to find datasheets or any particularly specific information about these parts, I feel like I'm probably too inexperienced to recognize any potentially generic components here and feel like someone is just going to rattle off some generic part numbers that I can look up. Hope that's the caseThanks for any help people can send my wayI've included some photos of the parts in question

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 10, 2019, 01:01:14 pm
content: I suggest just finding a ready made PSU that outputs 5V and +-15V, then getting an amplifier module to go with it.