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Restoring SX-3800, my first - a little background and a couple questions

Discussion in 'Pioneer Audio' started by John Hale, Feb 28, 2017.

  1. John Hale

    John Hale Member

    My first post with substance (hopefully). If you wanna skip the back story go to "XXXXXXXXX" below. about me I am not an EE or a lifetime electronics guy. I am however a Civil engineer and a lifetime audiophile. About 1.5 yrs ago My Meridian G68 made the magic smoke from the power supply. I knew I didn't have the money to replace the unit outright so, decided to learn and repair it myself..... and so it starts. Quite a benchful of test gear and self learning later here I am. I did manage to install a linear power supply to the Meridian and recap all the rest of my gear and happily all running again. When I look at my bench full of gear I probably could have purchased a new unit and then some but what fun would that be. So I decided to check out some of the gear from my youth that I lusted after and could never have. So first e-bay purchase a Pioneer SX-3800, next a Marantz 2265B, and bought locally (i live in Germany) a Technics SA-600. The SX-3800 arrived first so it is on the chopping block right now-- looking back maybe should have started with one of the others but I'm waste deep in it now.

    I have been reading and learning from this forum and know ya'll appreciate the "how did you get there" part of a restoration. here goes:
    The unit was powered up in the e-bay photos and was described as having "no Sound". looking ai saw that the back jumpers were not installed , I figured maybe somebody just doesn't know about that and I may get lucky.
    SO when it arrived I powered it up (knowing somebody recently did and I used my BK 1653 to bring it up slowly and limit current). Good news nothing blew up (yet). All functions seemed to be intact. so hooked up dummy load, Oscilliscope , Keithly 2015 to check initial operation. DC offset was R = -2.8mv, L=8.7mV (not Teabag, i thought). Started dinking around with a 1K HZ, 150 mV input -- THD wasn't to bad from pre amp section. so ran it through amp section one weak channel -- then got the smoke. I QUickly shut down.. I wasn't all that concerned since my plan was overhaul but didn't powerit up anymore and immersed myself in disassempling and cleaning (lots of pics for my reference for reassbly) SOrry so long folks I'll get to the point. WIth what I read on here and the great tips and advise I tackle the power supply board first. Tested ALL components with legs lifted or removed from circuit. RE-capped, Re-diode, Re-transistered the whole board with info learned from this forum (Thank You!)
    Now I'm working on the Amp Board (GWH 139-A) got the capps OK but I didn't find a transistor list. I pieced together info for 6 transistors in the middle of the board and 8 diodes but could use some help figuring the others specifically:

    Q102,Q101 - C1775
    Q110,Q105 - C1915
    Q122,Q121 - A904
    Q124, Q123 - C1914
    Q115, Q116 - A905
    Q111,Q112 - A750
    Q113, Q114 - C1400
    Q117, Q118 - A750
    Q125, Q126 - C2275
    Q127, Q128 - A985 (A1011 was what was installed) (drivers - hfe really varies between the two sides)

    Sorry so long winded. I haven't tested any of the rework yet (I know this is a mistake but the thing was SOOO grungy and I knew I was going through it all) so it is all disassembled. Plus I like working on one board at a time on the bench with wrestling with the whole unit.

    BTW - I desoldered the pin headers with wires attached thinking it would keep things in order - Wrong ! many of the plastic holders just disintegrated. I tried looking pin headers up and can find many but they specify Pitch (which I think id the pin dia.) but I don't see in the specs pin spacing-- most of what I measure is about 5mm except the header from the transformer which is about 9-10mm spacing -- is the spacing standard?

    Thanks so much for your help already and look forward to the future! Hope I did this right......


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  2. markthefixer

    markthefixer On Hiatus, dealing with Dad's estate full time Subscriber

    edit - Welcome to the Pioneer Audio Forum and silver face ownership. I have a lot of respect for civil engineers, an EE can fudge it a bit, but the CE has to get it right the ONLY time it's done or BAD THINGS HAPPEN.

    I believe I posted a list for the sx-3900, and while the "q" numbers may not be one to one, IIAC the PART numbers and circuit positions ARE. The amp and it's pc board are almost identical to the 3800, with one having 4 output transistors, while the other has 8 output transistors. The Power amps for the SX-D5000 is pretty much IDENTICAL to the SX-3800, while the D7000 and SX-3900 have the same amp card. There was one "bobble" in all these boards with parts of the protection circuit.
    So look at the SX-3800, SX-3900, SX-D5000 and SX-D7000 threads for AWH-097 parts.

    You have tackled a NSA amp circuit, a most unforgiving beast, that has to be 100% right on before power is applied - or not only with the original damage reoccur, but more will be done. This is not to discourage you, but rather to CAUTION you. Slow and steady with a LOT of patience will win the race.

    I can go on and on about the amp (kind of an expert) but I'll drop hints for further research into my posts.
    1. the power transistor sockets crack, there is a replacement scheme. A GOOD one.
    2. certain transistors run HOT, they have a THICKER center (collector) lead, BUT to meet their power dissipation specs, that center lead MUST be soldered to 1 square inch of copper foil on the board. Pioneer DIDN'T. Thus those transistors sort of unsolder themselves. I replace with to-126 case transistors which can shed the heat AND can accept a heat sink.
    3. sometimes on these units Pioneer went LIGHT on the wave solder, leading to solder joints that crack under normal thermal operating stress over time. A 100% hand resoldering of ALL the joints is recommended. You can check the apparently GOOD looking BAD joints by trying to move the lead - a good joint wont, these will.
    4. after a fault ALL NEW SILICON is STRONGLY recommended, including EVERY diode but the thermal bias diodes.
    5. (even I do this) you need to do 100% component testing - especially the resistors - and the resistors must be tested with one leg disconnected.

    You see, when something blows in the amp, a LOT of parts are RACING towards destruction, and the winners smoke, and the second place finishers turn up when you THINK it's fixed, and it blows up again.

    I'm EXPERIENCED with these things, and I have had blow ups where shrapnel from exploded transistors went flying past my nose.

    Once you get them running, they (the NSA amps: the sx-3800 & SX-3900) have the lowest distortion amps of most of the silverface, and they DO tend to be robust once their Achilles heels are corrected (cracked sockets, light solder and crystallized overheated solder joints)

    I love to get to these things while they are running - I STILL find all of the above, but they havn't yet damaged it and correcting the problems is a whole lot more fun (I do do a few preemptive replacements of certain amp transistors for longevity - and I have enough of them out there that I would hear about a re-occurrence of the problems.)
    Last edited: Mar 1, 2017
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  3. zebulon1

    zebulon1 Building a new bench. Finally! Subscriber

    Las Vegas Nevada
    I would like to try to repair one of these (SX-3800) some day.

    I had some time this morning.
    This is combination of past posts from MTF cira. 2010.
    I know for sure there are some obsolete part numbers but alternates can be found.

    Pioneer SX-3800:
    gwe-133 c3 cea 470m 25L 47uf 25v 647-UPW1V470MED 47 35
    gwe-133 c4 cea 470m 25L 47uf 25v 647-UPW1V470MED 47 35
    gwe-133 c12 cea 221m 16L 220uf 16v 647-UPW1V221MPD 220 35
    gwe-133 c30 cea 101m 10L 100uf 10v 647-UPW1A101MDD 100 10
    gwe-133 c33 cea 100m 50L 10uf 50v 647-UPW1H100MDD 10 50
    gwe-133 c36 cea 101m 25L 100uf 25v 647-UPW1V101MPD1TD 100 35
    gwe-133 c43 cea 100m 50L 10uf 50v 647-UPW1H100MDD 10 50
    gwe-133 c51 cea 471m 16L 470uf 16v 647-UPW1E471MPD 470 16
    gwe-133 c54 cea 331m 10L 330uf 10v 647-UPW1A331MPD 330 10
    gwe-133 c63 ceanl 2r2m 50 2.2uf 50v 647-UKL1H2R2KDDANA 2.2 50
    gwe-133 c64 ceanl 2r2m 50 2.2uf 50v 647-UKL1H2R2KDDANA 2.2 50
    gwe-133 c65 ceanl 010m 50 1uf 50v 647-UKL1H010KDDANA 1 50
    gwe-133 c66 ceanl 010m 50 1uf 50v 647-UKL1H010KDDANA 1 50
    gwe-133 c69 cea 100m 50L 10uf 50v 647-UPW1H100MDD 10 50
    gwe-133 c70 ceanl 010m 50 1uf 50v 647-UKL1H010KDDANA 1 50
    gwe-133 c71 ceanl 010m 50 1uf 50v 647-UKL1H010KDDANA 1 50
    gwe-133 c72 cea 010m 50L 1uf 50v 647-UPW1H010MDD 1 50
    gwe-133 c73 cea 220m 25L 22uf 50v 647-UPW1V220MDD 22 35
    gwe-133 c76 cea 101m 10L 100uf 10v 647-UPW1A101MDD 100 10
    gwe-133 c77 cea 101m 10L 100uf 10v 647-UPW1A101MDD 100 10
    gwe-133 c78 cea 470m 25L 47uf 25v 647-UPW1V470MED 47 35
    gwe-133 c79 cea 3r3m 50L 3.3uf 50v 647-UPW1H3R3MDD 3.3 50
    gwe-133 c80 cea 470m 10L 47uf 10v 647-UPW1V470MED 47 35
    gwe-133 c83 cea 101m 25L 100uf 25v 647-UPW1V101MPD1TD 100 35
    gwe-133 c84 cea 101m 25L 100uf 25v 647-UPW1V101MPD1TD 100 35
    gwe-133 c85 cea 471m 16L 470uf 16v 647-UPW1E471MPD 470 16
    gwe-133 c97 cea 4r7m 50L 4.7uf 50v 647-UPW1H4R7MDD 4.7 50
    gwe-133 c98 cea 3r3m 50L 3.3uf 50v 647-UPW1H3R3MDD 3.3 50
    gwe-133 c103 ceanl r22m 50 0.22uf 50v 667-ECQ-V1H224JL2 0.22 50


    amplifier transistors:

    Q101 Q102 2sc1775 ecb 90v 50ma .3w 200mhz 400-1200 hfe

    Q103 Q104 2sa979 dual transistor 100v 50ma .2w unkmhz 250-800hfe
    Q105 Q106 2sc2291 dual transistor 100v .1a .2w 100mhz 250-1200 hfe

    Q107 Q108 2sa750 ecb 50v 50ma .25w 100mhz 450 hfe
    Q111 Q112 2sa750
    Q117 Q118 2sa750
    Q109 Q110 2sc1915 bce 120v 50ma .80w 200mhz 150-800 hfe
    Q113 Q114 2sc1400 ecb 100v 50ma .25w 100mhz 500 hfe
    Q119 Q120 2sc1400
    Q115 Q116 2sa905 bce 120v 50ma .80w 200mhz 150-800 hfe
    Q121 Q122 2sa904 bce 90v 50ma .25w 150mhz 250-1200 hfe
    Q123 Q124 2sc1914 bce 90v 50ma .25w 150mhz 250-1200 hfe

    Q135 Q136 2sa985 bce 120v 1.5a 25w 180mhz 150 hfe
    Q133 Q134 2sc2275 bce 120v 1.5a 25w 200mhz 150 hfe

    Q125 Q126 2sc2575 bce 50v .2a .3w 200mhz 90-800 hfe
    Q137 Q138 2sc2575
    Q139 2sa1100 bce 50v .2a .3w 200mhz 90-500 hfe
    Q140 2sc1384 ecb 60v 1a .75w 200mhz 160 hfe


    Q101 Q102 - KSC1845
    . . . .
    Q107 Q108 Q111 Q112 Q117 Q118 - KSA992
    Q109 Q110 - KSC2310
    Q113 Q114 Q119 Q120 - KSC1845
    Q115 Q116 - KSA910
    Q121 Q122 - KSA910
    Q123 Q124 - KSC2310

    Q133 Q134 - KSC2073
    Q135 Q136 - KSA940

    Q125 Q126 Q137 Q138 - KSC2383YBU
    Q139 2sa1100 - KSA1013
    Q140 - ZTX1056A edit, use KSC2073

    Fairchild transistors from mouser.com, parts numbers:

    512-KSA992FBU (low noise)to-92 ecb 120v .05a .5w 100mhz 150-800hfe $0.05 ea
    512-KSC1845UBU (low noise)to-92 ecb 120v .05a .5w 100mhz 150-800hfe $0.05 ea

    start edit 9/12/2010 replacements
    512-KSA910YSHTA to-92 ecb 150v .05a .8w 100mhz 40-240hfe $0.07 ea Q115, Q116, Q121, Q122 9/12/2010 obsoleted
    512-KSC2310YBU to-92 ecb 150v .05a .8w 100mhz 40-240hfe $0.11 ea Q109, Q110, Q123, Q124 9/12/2010 large to-92 discontinued
    these (ksa910/ksc2310) ran hot...

    edit 9/12/2010 possible ksa910/ksc2310 replacements
    512-KSA1013YBU to-92L ecb 160v 1a .9w 50mhz 160-320hfe $0.17 (R=60-120, O=100/200, Y=160/320)
    512-KSC2383YBU to-92L ecb 160v 1a .9w 50mhz 160-320hfe $0.17
    512-KSA1220AYS to-126 ecb 120/a160 1.2a 20w 155mhz 35-320hfe $0.39 (R=60-120, O=100/200, Y=160/320)
    512-KSC2690AYS to-126 ecb 120/a160 1.2a 20w 155mhz 35-320hfe $0.40
    512-KSA1381es x to-126 ecb 300v .1a 1.2/7w 150mhz 40-320hfe $0.27 ea
    512-KSC3503estu to-126 ecb 300v .1a 1.2/7w 150mhz 40-320hfe $0.28 ea

    original transistors:
    2sa985/a pnp to-220 bce 120v/150v 1.5a 25w 180mhz 35-320hfe orig 180mhz nsa driver
    2sc2275/a npn to-220 bce 120v/150v 1.5a 25w 200mhz 35-320hfe orig 200mhz nsa driver

    757-2SA1930(Q,M) pnp to-220 bce 180v 2a 20w 200mhz 50-320hfe 200mhz nsa driver
    757-2SC5171(Q,M) npn to-220 bce 180v 2a 20w 200mhz 50-320hfe 200mhz nsa driver
    old and slow:
    512-KSA940TU_Q pnp to-220 bce 150v 1.5a 25w 4mhz 40-140hfe $0.54 Q135, Q136
    512-KSC2073TU npn to-220 bce 150v 1.5a 25w 4mhz 40-140hfe $0.54 Q133, Q134

    9/12/2010 end possible replacements

    and this one from zetex
    522-ZTX1056A NPN TO-92E ebc 150v 3a 1w (Vce(sat)=0.3v @ 3a) 120mhz 30-1200 hfe editt no longer available, use:
    512-KSC2690AYS to-126 ecb 120/a160 1.2a 20w 155mhz 35-320hfe $0.40

    This applies to the sx-3800, sx-d5000 (both with allowances for q numbers), sx-3900 and the sx-d7000.

    There is a minor difference in the protection circuit, the Q139 2sa1100 WAS 2sc2575 in the older circuits, but in later models of the 3800 and 3900 and in all D5000 & D7000 units, the polarity of the protection voltage from the power supply (-25v) was reversed (to +25v), and the circuit rewired.
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  4. John Hale

    John Hale Member

    Awesome and Awsome! Thank You both! Exactly what I needed. Mark - yes sir to all of that. I have read many of your posts, I am not to savvy on searching these thread (thus the reason I couldn't find your list) but it makes me read a whole lot of stuff. I have paid attention and yes I have tested EVERY component thus far. Which, I guess cuts down by half of how many solder joints are left to be retouched. Zebuion1 thanks so much will get busy checking my stock and putting together an order. I failed to mention earlier that yes one output transistor was shorted. I have got the SANKENS (C2921,SA1215 both sides) from Digikey. good news - seems like a good physical fit, bad news - one set does not come with mica (or any) isolators and finding this shape is a problem. I may have to order others just to get the isolators. Of other good news interest upon inspection of the output connectors, they seem to be in good shape and not brittle or burned in any way.

    I really am thankful for your help-- I know you guys are experts , I'm sure also it is a long slow road (that's for you Mark) to completion.
  5. markthefixer

    markthefixer On Hiatus, dealing with Dad's estate full time Subscriber

    My doctor was waffling about something a few years back, and I made a comment about something in the past he didn't know. That IMMEDIATELY switched him over from waffling, to INSISTENT upon a particular course of action.

    A blown output transistor on the four mentioned models does exactly the same for me -
    four mouser 651-1757022 output transistor connectors will only be 11 bucks, REPLACE THEM.
    Probably less than the replacement transistors when it pops again. Not IF, - WHEN.

    I also think I know where you will find loose solder joints on that board. No less burned resistors.
    You probably also lost some emitter resistors, the dual square ceramic ones 2 x 0.47 ohms.
    You are lucky it didn't use the protection system to leapfrog into the other channel.
  6. KingBubba

    KingBubba "Too Much Stuff" Subscriber

    Brooksville, Fl.
    I attempted to do the Deoxit cleaning to the switches and pots on mine. The aux switch would have to be cycled many time to listen for a short time. The selector switches run through the frame with a long plastic angled piece that applies the action to the actual switches in the back or the receiver. Taking the long plastic pieces out is no problem, but OMG, putting them back in is true hell. Somewhere in the process of returning my plastic rods to their original places, I apparently botched something up. When I fired the receiver up on the dim bulb, it immediately started having the smell of magic smoke. Somehow I killed my great receiver, just trying to do a cleaning. I will never enter one of those ever again and mine sits in the garage dead and collecting dust. I am still broken hearted even though this happened 7 years ago.

    I bring this up as a warning about the process of putting the 3800 back together. It is a dangerous game. Maybe MTF or one of the others might have suggestions on how to avoid the troubles you will soon encounter with the selector switches. Good luck on a great receiver with some great blue flouroscan.


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  7. John Hale

    John Hale Member

    Point Taken on the connectors I did replace some toasty resistors already - I think MTF you have mentioned these before. 220 ohm ones and another I don't recall the value right now. They had surounded a film cap, which I have replace all four Like capps on the board. Also the ones between the driver trasistors. I did test the emitter resisters- they seem to check out fine- and no evidence of excessive heat. Still awaiting my transistor shippment. I appreciate everybody chimming in -- Good caution on the plastic switch pieces - I've got them all out.
  8. John Hale

    John Hale Member

    Oh I almost forgot-- While I am getting connectors can ya'll provide any info on Pin headers? Based on the fragile nature of these I think I want to do a wholesale replacement of those as well. to re-iterate my hang-up - it the pin header specs it provides a Pitch (I assume to be pin Dia or thickness) but I don;t see the pin spacing anywhere in data sheets. Most on the unit seem to be about 5mm pin spacing except the power one that is about 9-10mm

    Thank You
  9. John Hale

    John Hale Member

    Wondering if I should be concerned--- I got the transistors ,as outlined above and as I'm checking to match and confirm pin outs I'm seeing differences between them and the in place originals. I guess I would expect that new would be higher hfe than the old but the opposite is the case in almost all cases thus far. for example
    Q109,Q110 OLD hfe 433,435 new hfe 216,216 C1915 vs KSC2383
    Q121,Q122 OLD hfe 363,400 new 247,272 A904 vs KSA 1013YBU
    Q123,Q124 OLD 506,521 new 216,216 C1914 vs KSC 2383YTA

    Or should I just be concerned with matching the best I can between both sides?

  10. USMC Spike

    USMC Spike Active Member

    Tejas, North Central
    Hi John,

    Just thought I'd add my .02 cents to what I've found from markthefixer (MTF). Besides the high complements
    he receives here, I also am a student, went back to school to learn some EE Technology and get another degree
    in it, and as a mature student. So, after going through DC, AC, and currently solid state devices...Virtually everything that MTF has been preaching here and warning us how to go about researching and fixing these things, along with what is important, and in what order, on the data sheets is exactly the same thing my profs have told me or are telling me in class.

    One example, seems obvious but I guess not. Don't listen to those who tell you how to install the transistors,
    ALWAYS look at the data sheet and check them for yourself. Verify the pin configuration and the parameters.
    Double check them on the source documents too.

    It's essentially about being self reliant, being a student of the electronic's art, and learning it's always best to take
    the time to do the proper research before we go digging into anything...how ever simple, to verify from the data sheet and schematics, then taking proper care and good practice to implement it.


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  11. John Hale

    John Hale Member

    Thanks Spike! I think I am tracking with the message. At the moment - I have halted work on the Amp board awaiting some sage advice on the question above concerning transistor wholesale transistor replacement. I test every component. Especially transistors for the reasons you state above -- that is what prompted me to start asking about Hfe values of new transistors vs what I had measure on the originals. I used to think you could just match up the shape But I know better now and put them on the chineseum transistor testr to double and triple check pin outs, etc.

    I am now trying to trouble shoot the pwr supply board. The voltages I am checking do not necessarily match up with what is specified so, I'm ensuring I track all this down completly before hooking anything to it.
    I go pretty slow (and like to think methodically) but sometimes I just have to walk away and think about things overnight (or whatever). I really appreciate the dialogue and great participation of this group!

    Spike if USMC spike stands for what I think ,maybe I should have a call sign USAF John


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  12. John Hale

    John Hale Member

    In troubleshooting the power supply - I was not getting expected voltages very early in the system. like D 204,201,206. Not much between this point and the tramnsformer. D 204 -109V (-62.5), D201 +30 (+62.5), D206 +34 (21). I pulled the fusses and measures AC input Pin 1 50, Pin 2 50, Pin 3 1-2 V, Pin 4 13, Pin 5 1-2V. I tested with Oscilliscope and it revealed that when fusses in place I was geting (you guessed it) -30V DC on pin 3 and -12V DC on pin 5-- accounting for the discrepancy at the diodes. IS there supposed to be a DC offset returning to the transformer windings? any clues are appreciated. No other circuitry is attached to the pwr supply board other than the tranformer inputs and two grounds (pins 19 and 33).
  13. John Hale

    John Hale Member

    Sorry meant to say +12V on pin 5
  14. markthefixer

    markthefixer On Hiatus, dealing with Dad's estate full time Subscriber

    When an older power supply blows, or I do a restoration, it gets all new silicon and electrolytic capacitors, it's far more costly to it's reputation to be constantly removing it from service and opening it up to chase some transistor that was damaged but hadn't died in the initial failure compared to the time and wear and tear of reopening it again and again - I'm AT the board, so I FIX it so I don't have to go back again and again for for some pocket change transistor.

    pay close attention

    pins 4 and 5 AC are floating with respect to ground, thus paying attention to WHERE you place your ground probe is critical. Use pin 19 or chassis.
    Also THAT circuit is a DOUBLER, an 8vac winding making closer to 20 (depending upon the load - look up floating voltage doubler).

    Don;t be too concerned what you read at the caps - as long as the 2.2 ohm series resistors are OK, use the collector voltages of Q201 (+62) Q206 (-62), Q209 (about 20) & Q210 same (about 20). The 2.2 ohm resistors are intended to act like fuses, thus the 1/4 watt rating and the exclamation point in a triangle symbol. I laid in a stock of them long long ago. The service manual code also reveals these to be "flameproof" resistors - which is usually a varnish covering that resists flames shooting out, just allowing copious quantities of magic smoke.

    The +47v supply is the master supply, all others need it to work. it is set by d207(14v), with feedback element q203 controlling series pass element q201. R208 and R209 provide the feedback voltage (14.6) that will be regulated to 0.6v GREATER than the D207 (14v) reference voltage. The regulator needs to be turned on / powered up (startup) at q203 collector. This is a critical point because noise and hum WILL be passed along to the regulated voltage. In earlier models Pioneer used a Resistor / capacitor filter with the capacitor as big as the main storage cap: c203 at 220uf. This was a bit awkward so they changed it to a constant current circuit, which would REJECT the garbage. R206 and Q202 are a constant current regulator.

    The +32v supply is a simple proportional regulator Q204, set by the voltage divider R214, R215, and subtract 0.6v for the output voltage and a skosh more for base current. The -32v with Q208 is the same thing in the opposite polarity, while it is tapped off a rather interesting voltage divider: R211, R212, R213.

    The -47v supply is a MIRROR regulator. Again Q206 is the constant current startup supply, while Q205 is the series pass element controlled by the Q207 feedback element. BUT THIS CIRCUIT uses a ZERO VOLT reference. The Q207 emitter is grounded, thus it will want to maintain it's base at -0.6v. The voltage divider: R211, R212, R213.is arranged so that at +47v and -47v the junction between R213 and R212 is at -0.6v.
    R213 is 8200 ohms, while the total of 8000 ohms is achieved by R212 5600 ohms and R211 2400 ohms.

    If that isn't obfuscated enough, the +14v from D207 is used to drive driver Q211 and pass element Q209 in a Darlington configuration, FINALLY nailing down the floating pins 4 and 5 AC to a damn GROUND!! The 14v cost in this circuit is 2 x 0.6v leaving 12.8v

    Finally, the 5.5v from Q210 pass element is another proportional divider of R226 620 ohms and R225 560 ohms reading pin 16, which comes in from the function switch board with switching and diode steering logic. I suspect it's for the frequency display.

    There are other tricks, like for the Flouroscan Frequency Display, feeding a few volts AC to the heaters with a negative DC bias voltage impressed (D213 -32 +17.7 = -14.3v)

    Now go back and reread this a few times, it's one of my infamous information dumps, and it did take quite a while to put together to my satisfaction.
    Hope your brains didn't melt and run out of your ears!!!
    Last edited: Mar 8, 2017
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  15. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Glen Burnie Md.
    Now THIS is the kind of POST I remember from 8-9 years ago. HEADY DAY's back then.
  16. zebulon1

    zebulon1 Building a new bench. Finally! Subscriber

    Las Vegas Nevada
    That's an understatement


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  17. John Hale

    John Hale Member

    Thank You, SIr - My brain is not melting but it will take some time to digest and test. Did I say thank you yet? What is "floating voltage" (ha just kidding). I better get to work figuring this out. I know it takes time and effort to put something like that together -- but new guys like me would probably throw in the towel without it!

    Much appreciated and VERY impressive
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  18. quaddriver

    quaddriver 120 What's per channel Subscriber

    Its like watching the original 'White Christmas' with Bing....Its fricken art.

    We still gotta figure out a way to hook a 1Tb drive to MTF and do a data dump! I got the boys in R&D workin on it...
  19. John Hale

    John Hale Member

    Well folks - While I still am digesting MTF's info. I went ahead and did some measuring. Three 2.2 Ohm resistors are intact and spec. All Collectors referenced to chassis ground.
    Q201 (+62) Measured +40.7V DC with 8.7 V AC @ 5.7 Hz frequency
    Q206 (-62) Measured -37V DC With 1.8V AC @ 6.5Hz Frequency
    Q209 (about 20) Measured +42.9V DC
    Q210 same (about 20). Measured 2.3 V DC with 10V AC @ 6.5 Hz Frequency. However, once powered down it settles to a nice DC voltage of about 25V (I am assuming from Caps)

    Addionally, Q 210 measures -1.75V DC at the emitter

    While not very close to spec value, most seem in the neighborhood (other than the AC) except for Q210. I,ve been tracing through schematics and components on the board but I cannot work it out yet. As I have said before, All electrolitics replaced, Double checked polarity, all diodes replaced, all transistors replaced (double checked pin outs) all remaining resistors all tested and pass with one leg pulled.

    I'm not sure if there is some interaction that needs to take place with other boards. At this point I only have it connected to input power and two grounds (pin 19 and 33). Well it was kind of a frustrating day, so I'll walk away overnight. ANy help is sure appreciated.

    Thank You
  20. markthefixer

    markthefixer On Hiatus, dealing with Dad's estate full time Subscriber

    Q201 collector(The TAB!!) at +40.7v is low. Q206 collector is correspondingly low. These are RAW DC voltages fresh off the storage capacitors. They are WAYYY too low.
    They need 62v to make their regulated 47 volts at the output!!

    Are you on a DBT? Either remove it entirely, or tell me what wattage bulb you are using so I can tell you how much to increase it.

    Measure AC volts between pins 1(red) and 3(black) , and pins 2(red) and 3(black).
    Then check the fuses FU2 and FU3. REMOVE them for an ohms check.

    It looks to me like half your power is missing. Sometimes one of two fuses being blown does that.
    Other times a diode (d201 - D204) has popped, but that causes just one polarity to be lower voltage.

    Once you get further along:
    The junction of D207 cathode and q203 emitter MUST be at +14v referenced to a chassis ground.

    And what's with this 5.7hz frequency? It's meaningless as far as I can tell.

    How did you measure the 8.7 V AC part of it.
    What is the make and model of your DMM?
    Do you know if it has a blocking capacitor for AC readings that have a DC voltage present?

    Guys I am NOT yet "back". In fact my BIGGEST time crunch of the year is approaching quickly and I am striving mightily to make it.
    As such, I cannot continue to devote the time levels I have recently burned here.
    ANYBODY is welcome to use the information I posted (it was posted as a road map to help GUIDE this repair if all new silicon wasn't implemented)
    to help along on this repair. My toes are NOT nor will be being stepped on.
    Overundr1 likes this.

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