Pioneer M-73 amplifier from the 1970 era - Looking for schematics and info - Page 1
Forum section: electronics / repair

author: AndersJ
author_rank: Frequent Contributor
timestamp: March 29, 2021, 05:45:13 pm
content: A friend of mine is trying to repair a Pioneer M73 amplifier from the 1970's, not the 1990's model.He tells me he is stuck, since it easily oscillates and/or gets instable.Does anyone have:* Insights into possible difficulties with the older M-73?* Schematics or other service information?* Any clues to why the 2SK389 dual FET easily and often fails

author: drussell
author_rank: Super Contributor
timestamp: March 29, 2021, 07:06:20 pm
content: I don't see any links to the 1977-1980 model M-73 manuals, only that it was supposedly a Japanese-market-only model and the schematic is supposedlysimilarto the SPEC-4, but it is physically smaller (and only rated 85 W/channel instead of 150?) and the board layout is different...Itmighthelp with tracing the basic circuitry, though...Pioneer SPEC-4 Stereo Amplifier Service Manual(File is slightly too large to post directly to the forum.)https://audio-database.com/PIONEER-EXCLUSIVE/amp/m-73-e.html(This does list the input voltage spec as 100V.)

author: floobydust
author_rank: Super Contributor
timestamp: March 29, 2021, 08:19:24 pm
content: 2SK389 you can get from Linear Systems. They've re-released 2020-01-21 theirLSK389to even lower noise en = 1.3nV/√Hz.These parts have no overload or ESD protection in most circuits and get damaged from connecting RCA jacks.Given the amplifier's age, it will need to be re-capped first. You can sketch a schematic too, I do that using pics of the top and bottom side of the pcb.

author: coromonadalix
author_rank: Super Contributor
timestamp: March 29, 2021, 10:50:47 pm
content: from 1992 to 1996 ?? not sure of the similaritieshttps://www.hifiengine.com/manual_library/pioneer/m-73.shtmlRegister its free ...

author: drussell
author_rank: Super Contributor
timestamp: March 29, 2021, 11:04:06 pm
content: Quote from: coromonadalix on March 29, 2021, 10:50:47 pmThe service manual for the 1990 model is readily available, but that is not the unit the OP is looking for, which was made from 1977-1980.I also have that version mirrored here:Pioneer M-73 (1990 version) Stereo Amplifier Service Manual(Yes, Pioneer likes to re-use identical model numbers for completely different products.)

author: drussell
author_rank: Super Contributor
timestamp: March 29, 2021, 11:16:55 pm
content: Additional data points from the compiled Pioneer model number database, for reference:

author: drussell
author_rank: Super Contributor
timestamp: March 29, 2021, 11:53:15 pm
content: Oh, and here is a copy of the SPEC-4 (M-75) service manual with more readable schematics:Pioneer SPEC-4 Stereo Amplifier Service Manual w/readable schematics

author: floobydust
author_rank: Super Contributor
timestamp: March 30, 2021, 02:32:19 am
content: Pioneer did the same with theA5,the newer one is just a cost improvement, circuit is totally different, no dual JFETs- just to cash in on the old model number fans I guess.

author: AndersJ
author_rank: Frequent Contributor
timestamp: March 30, 2021, 06:08:10 am
content: The saturn-tech links seem to be broken.Perhaps it is a temporary issue.

author: drussell
author_rank: Super Contributor
timestamp: March 30, 2021, 01:22:28 pm
content: Quote from: AndersJ on March 30, 2021, 06:08:10 amTry them now...That server is multi-homed and the main address on the fiber wasn't routing properly, apparently...