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Sencore SG165 - AM/FM Analyzer - Repair

The thickness of the 400 hz signal is the 19khz MPX signal superimposed upon the 400 Hz L and 400 Hz R signal.
 
Ragwire said:
Nice work!
(How is it you got probes when you bought the SG? Isn't including factory probes with any instrument you sell in violation of some federal law?)
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everything is a violation of some state, federal, or local law now these days
 
OK hooking up the L channel is at a higher frequency in the RF versus the R channel. L channel is pretty distorted.
 
OK hooking up the L channel is at a higher frequency in the RF versus the R channel. L channel is pretty distorted. OK at 108Mhz adjusted both the antenna trimmers and RF trimmers on both the L and R channels. The R channel has much more noise. OK now going back to 88 Mhz both L and R channels track with sine waves at the same frequency.
 
OK I noticed that I have not checked every single passive on the MPX board, as there are many resistors I have not checked, and perhaps that is the reason why the inductors and transformers do not tune properly.
 
MarantzRefrb said:
Thanks! I hadn't heard that the probes would cause any problems (especially with the law), they're a pretty simple circuit, and are being reproduced on eBay right now. If you search Sencore SG165 on eBay, the repro probe kit should be the first thing that comes up.

This SG165 being so complete, is was what made me buy it, despite the seller disclosing the entire FM RF was blown out.
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Just trying for a post on this subject. I recently bought SG165 from ebay seller. Repaied the power supply problems and have moved on to fact of missing FM rf not working. I have read through this 2 year posting and can possibly fix mine now. My instrument is marked Run 11. I think I have a direction to go will up date as I move through R/R. Thanks for the help here.
 
Have two scopes, Tek 2445 and Rigol DS2202A. The tek is 150 meg. H, and Rigol is 200 meg Hertz. Recently purchased new freq counter, BK PRECISION 1803D becausemy other digital counter would not lock on to freq I was working with on SG-165. The 1803D works great for fm and am. I have a copy for SG-165 with all its charming undersized schematics. Been making note of Sencore booboos from this thread. Just order the noted NTE transistors for rf board from NTE online. So now the disassembly of board from cabinet and clawing my way through circuit.
 
I've encountered the same thing with a counter on a couple of SG165s. It seems that many generic signal counters have a minimum signal threshold for reliable operation, and that is above the normal signal amplitude of what some of these alignment units can produce, even when they are working properly. The 'scope is your better bet.
 
Watthour said:
I've encountered the same thing with a counter on a couple of SG165s. It seems that many generic signal counters have a minimum signal threshold for reliable operation, and that is above the normal signal amplitude of what some of these alignment units can produce, even when they are working properly. The 'scope is your better bet.
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I keep looking for the ultimate "fix itself" tool/instrument, just haven't found it yet!
 
Jdmccor said:
I keep looking for the ultimate "fix itself" tool/instrument, just haven't found it yet!
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I do like the minisa spectrum analyzer, and adapt it with a 30 inch coiled wire acting as an antenna and I can then pickup
rf over 100khz. but a scope with 150Mhz bandwidth is also very very useful
 
backmd said:
Why thank you Kent! So with the Sencore SG165, I am now open for business for alignments.
Resume
In high school took electricity for one year with a gifted Navy radioman, what an excellent teacher
In high school took electronics for one year with that same gifted Navy radioman, still an excellent teacher, very lucky to have him
Had the opportunity to get a class D radiotelephone license, do not know if it is current
Completed a bachelors in bioengineering at the University of Illinois wonderful teachers here
Worked at Motorola as an intern in the crystals division in Schaumburg IL
In my fifties worked on four NRI tube radios starting with AM alignments using a 455Hz sine wave generator made by Knight kit
In my middle fifties to early 60s worked on many tuners;
Adcom GFT-2 4 electrolytic replaced on 6-6-15; replaced fuse with ¼ amp slow blow SB
Adcom GFT-555
Adcom GFT-555
Carver TX11
Dynaco AF6
Dynaco FM3 aligned on 11-4-20 stereophile class B has PEC upgrades and 4 capacitor
upgrades uses diode matrix and LC IF
Dynaco FM3 aligned on 11-7-20 stereophile class B has PEC upgrades and 4 capacitor
upgrades uses diode matrix and LC IF
Dynaco FM3
Dynaco FM5 modified chip MPX
Dynaco FM5 stock
Kenwood KT5500 stock new light bulbs times 3
Kenwood KT5500 stock new light bulbs times 1 wired in series!
Kenwood KT7500 bulbs, OPA2604, AD823, then OPA627BP, polypropylenes Schottkeys, bypassed 75us switch
Knight KG795 has 4 gangs and LCIF and diode matrix MPX
KLH 18 WB uses diode matrix and LC IF stereophile class B
KLH 18 WB uses diode matrix and LC IF stereophile class B
Needed meter surgery and meter face is upside down, gluing veneer
Mcintosh MR71 needed MPX work (lots) and silicon rectifiers and 6BM4A stereophile class A uses diode matrix and LC IF
Optonica ST3636 5 gang tuner
Philips AH6731 needed adjustment of center tune meter number 7 on fm tuner info
LC IF but chip MPX
Pioneer TX8100 aligned in 2008 WB black cabinet
Pioneer TX9100 modified polypropylenes WB swap cabinet; now walnut cabinet
Pioneer TX9800 feet replaced modified with Schottkys and 2 polypropylenes SB
Pioneer TX-9500 stock WB
Revox B760 needed a transistor and capacitor for power supply, meter transplant, alignment, 3 watt lamp, 4 24 volt lamps, 2 CA3053 can ICs, ceramic cap,
painted grey, toggle switch repair LCIF chip MPX number 8 on fm tuner info
Sansui TU-555 WB uses diode matrix and LC IF
Sansui TU-317 just moved tuning cap a little and it unseized
Sansui TU-517 highly modified with polypropylenes and Schottkeys
Sansui TU-717 modified polypropylenes 90 v Schottkys
Sansui TU-717 stock repaired with zener diode
Sansui TU-717 stock with hazy plastic two new transistors bad EC junction in small signal transistor
Scott LT112B broadcast monitor tuner sleeper uses diode matrix and LC IF
Scott LT112B broadcast monitor tuner sleeper uses diode matrix and LC IF
Tivoli Audio Model Two Stereophile class D 2007
Tivoli Audio Model One Stereophile class D 2014
In 2020 bought 10 tube tuners and 3 transistor tuners from facebook marketplace fixed them up and sold all but the venerable Scott LT112B because that is a great keeper tuner

So give me your tuners to work on for alignments! with bad RF sections, bad IF sections, bad discriminators, bad MPX sections, bad audio sections. I have a Sencore SG165 signal generator for MPX alignments, a Tektronix 150mhz four channel scope, several other Knight and Eico signal generators, Radioshack and B and K frequency counters, Sencore cricket transistor testers, RCA senior voltohmyst VTVM for discriminator alignments, Fluke multimeters. B and K capacitance meter, Tiny SA spectrum analyzer. I just enjoy this as a hobby and will help others on Audiokarma, now that I may be qualified.
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Gotta thank my lucky stars, I am repairing part time professionally now. I really really enjoy it!
 
I love a mystery ; so after 40+ years in electronics/electrical and mechanical refrigeration I look forward to sitting at bench and tearing down old instruments. Just got back to working on my SG-165 because of other projects. So am diving into the fm rf problem. Checking all the transistors now and found one ,#310 I believe installed as npn when the print says pnp. Also noticed there is no tr319 on print but I have one on my board. So another mystery, will remove tomorrow and check thetransistor with a meter properly. I bought a Sencore #26 transistor tester about 6 weeks ago and just finished cleaning it up, works fine. More later.
 
mrk229 said:
While ideally it would be great to have a 75 ohm match, the 100 ohm solution should be good enough. The idea is to keep a fairly constant ohmic value (impedance) as you go from one end to the other.

View attachment 2021879

This is from the SG165 schematic. Look at what happens to each element at the shaft is turned. Full clockwise R10A is bypassed but R10B is full resistance.
Go counterclockwise and you get the opposite effect. In the full CCW position, R10B is a short to ground so no output.
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I have an SG165 that is in need of the 75-ohm L-pad, it now has a 75-ohm pot installed that was replaced before me. Has anyone come up with a viable way to create the L-pad?
 
If you still have your original L-PAD: I rebuilt mine with parts from newer Clarostat pots. Need a heatgun to separate these.
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