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Old 24th August 2010, 12:56 AM   #1
mdynac is offline mdynac  United States
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Default Marantz 115b

i am in the process of recapping, etc my 115b.

the P400 power supply now has all lytics, save the audio coupling caps, changed, along with the reference zener H404.

the P150 AM radio lytics were changed.

and 2 power supply caps on the P300 MPX board.

has anyone ever worked on or modded these tuners ?

i have several questions.

i need the specs or datasheet for the following two components:

20A90M detector diodes

CFS107M ceramic filter


any help would be appreciated.

so far what i have done has made a significant improvement.
the power supply being the biggest.















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Old 30th August 2010, 11:23 PM   #2
mdynac is offline mdynac  United States
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okay i just finished recapping the P200 fm if board, it just keeps getting bettter and better sounding.

i have questions about the ratio detector diodes, aren't there any rf gurus out there????
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Old 1st September 2010, 05:08 PM   #3
kevinkr is offline kevinkr  United States
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Leave the diodes alone unless defective. There are all sorts of parameters you need to take into account and using the wrong diode will adversely affect the balance and ultimate AM rejection of your ratio detector. Nothing to be gained performance-wise unless bad. (unlikely) Replacing those diodes would necessitate a realignment of that transformer.

WRT to the ceramic filter it may be possible to replace it with something better, (more symmetrical skirts, better selectivity, improved group delay characteristics, etc. might be possible) a question to ask over at the fmtuners listserv. Again I would expect to have to perform a full realignment. Filter replacement is probably best left to one of the pros.
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Old 1st September 2010, 08:46 PM   #4
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Quote:
Originally Posted by kevinkr View Post
Filter replacement is probably best left to one of the pros.
Agreed.

It may not be a bad idea to test the old filters, as they do age and may go bad, but testing them requires at least a sweep generator and scope, even better a network analyzer (plus a little homebrew adapter PCB with BNC connectors, matching resistors and a filter socket).

How many filters does this thing have? If it's like 8, they're probably single-element ceramics (long out of production), in case of 4 they'd be more conventional 2-element types. The latter could be swapped for modern-day 280 kHz types with (usually) far less insertion loss or whatever else is deemed appropriate, but again an IF realignment is likely to be due.

I'd say the next best thing to perform after replacing all those aging electrolytics would be a complete realignment, especially if sensitivity seems low or uneven and dial readout is inaccurate. However, a full realignment requires at least a low-distortion FM generator, which generally is not something the average tech will have. RF alignment, however, can be performed reasonably well even by ear, provided some experience and the required alignment tools are present.
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Old 2nd September 2010, 12:35 AM   #5
mdynac is offline mdynac  United States
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thx much for the replies.

as for the ratio detector diodes, i will leave them be, i was just curious about the specs of those items. sooner or later i'm gonna need some.....
just that the newer schottky diodes with low Vf and excellent group delays may blow away the older germanium( i think) ones.
i just wanted to compare specs. but some where on this planet i will find the datasheet for the 20A90M diodes.

i sat in front of a network analyzer for 3 years at my last job, but i no longer have access to one. i do have a tek 465b sope, FG504 40 Mhz fun gen, PG508 pulse gen, DC510 counter
i did not think that any of these items would help me too much in aligning an FM stereo tuner......but i may be wrong. if you have a method of testing ceramic filters with the above test equipment, i would appreciate a test set up so i can attempt to do it myself.

i have been an electronic tech for 30 yrs, but although i did component level radar repair in the Navy, i have not touched anything RF in like 20 years except for the last work i did at 800 - 900 Mhz analog cell phone stuff.

there are only 3 ceramic filters in the if strip. the part numbers are in the first post.
they have CES (probably the manufacturer) on each part they are 3 lead, red with a white dot. the schematic looks like they are dual element, thats all i know about them. again, it would be great to get some data on these older components.

thanks in advance

mac
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