Pioneer Tuner/Amp repair [FIXED] - Page 1
Forum section: electronics / repair

author: on4top
author_rank: Regular Contributor
timestamp: December 27, 2016, 01:35:11 am
content: Go a pioneer tuner/amp from a friend with no audio output .Display lights up fine / tuner ect .. just no sound .My first observation was "protection relay is not turning on"The protection relay seems driven by a DC Detection circuit .Further investigation seemed that -19V is present on 2 final transistors their Emitor .. Q3 & Q1 .Q2 & Q4 no dc voltage on Emittor ( wich is ok )I desoldered all final transistors en checked them .. all fine .But still on the Emitor connection on the PCB .. stil -19V where Q3 & Q1 use to be soldered on .Checked most components on the amp section of the pcb .. emitor resistors / drive transitors / diodes nu luck yet finding a short transistor or capacitor ?Service manual / schematic -http://www.kallhovde.com/pioneer/tricomp/Audio/SX/SX-1300_2300_ARP1477.pdf

author: KhronX
author_rank: Frequent Contributor
timestamp: December 27, 2016, 01:44:04 am
content: If one channel is ok, you can take comparative voltage readings between the two channels ("good" vs. "bad").If you've got a negative DC voltage on the output, that would indicate that Q511 and/or Q507 are (nearly) fully on, and pulling the output toward the negative rail.

author: richnormand
author_rank: Unknown
timestamp: December 27, 2016, 02:05:33 am
content: Do I assume both channels are same?There is an overload circuit in the output amp, triggered, does it shut down both channels?Voltage at collector of output trans?Main PSU voltages OK to amp section. Look for the big caps and ensure voltage is OKMultifunction switch OK?R534 and R533 OK?Any "hiss" on the output, or any voltage offset or a "thump" when turning on?If you have a scope can you follow the audio from either the tape or phono input? In particular for audio output from the buffer stage.SP switch assembly OK?

author: KhronX
author_rank: Frequent Contributor
timestamp: December 27, 2016, 02:14:11 am
content: If you had read the OP a bit more carefully, and taken a peek at the linked schematic (hint: page 7, middle-bottom), you'll get an easy answer to most of your questions1) The -19v is present on only ONE of the amp's two channels (Q1 and Q3 are the output transistors of the bad channel); no DC on channel two (Q2 & Q4)2) See schematic (hint: yes, both channels go through two contacts of the same relay)3) Voltages likely ok, but waiting for confirmation4) Switches unknown5) Since the relay's open (due to the protection circuitry getting triggered from the -19v on one of the outputs) i'm preeeeeeeeetty sure there's no hissEdit due to edit: Good question about the emitter resistors...The amps are AC-coupled (through C501 and C502), so whatever's causing that huge DC offset is most definitely restricted to the power amp section itself.Quote from: richnormand on December 27, 2016, 02:05:33 am

author: on4top
author_rank: Regular Contributor
timestamp: December 27, 2016, 01:26:12 pm
content: Thanks for all reactions !Tonight i do some more checking .. i would like to find 1 part i can remove so voltage is gone on output .Then 1 channel should work ( relay should switch on when no DC is present on output )

author: KhronX
author_rank: Frequent Contributor
timestamp: December 27, 2016, 02:00:10 pm
content: Well, if you don't care whether the bad channel gets fixed or not, the only part you'd need to remove is the resistor going from the bad output, to the DC detection circuitry - in this case, R557 (10k).

author: mzacharias
author_rank: Frequent Contributor
timestamp: December 27, 2016, 02:01:10 pm
content: At a glance - I would check IC601, a 78M12 regulator, since you seem to be missing an offsetting positive bias on both channels. Been repairing audio > 35 years.

author: KhronX
author_rank: Frequent Contributor
timestamp: December 27, 2016, 02:20:44 pm
content: The odd thing is, unless i've horribly misunderstood something, that -19v offset is present at only ONE of the two amplifiers' output.That kinda makes me doubt the actual issue is common to both channels. But i stand to be corrected, of courseQuote from: mzacharias on December 27, 2016, 02:01:10 pm

author: mzacharias
author_rank: Frequent Contributor
timestamp: December 27, 2016, 03:18:53 pm
content: Quote from: KhronX on December 27, 2016, 02:20:44 pmSorry - mis-read your post. Funny thing is - I had a whole list of stuff pertaining to one channel, then ash-canned it when I read your post to mean both channels malfunctioning.In addition to basic checking transistors, I would check for bad resistors, such as R520 and R522, and if they are good, measure the voltage drop across them in operation. Voltage readings are key to determining which part of the amp circuit is malfunctioning. For example, if Q505 or 506 showed an abnormally high voltage reading across the emitter-base junction, then either that junction is reverse-biased somehow or the junction is open. Likewise - the voltage readings emitter-base of each output transistor may point to which 1/2 of the circuit is malfunctioning (the positive or negative half, that is).

author: on4top
author_rank: Regular Contributor
timestamp: December 27, 2016, 09:02:10 pm
content: Quote from: KhronX on December 27, 2016, 02:00:10 pmRemove R558 ( 10K ) en yes now relay is working and we have sound on the "Right Channel"Seems the -19V is on Q2 & Q4 and not Q3 & Q1 ... messed up in previous post .R557 is stil in place so no DC on the Right channel with Q3 & Q1 i soldered back in place now .Voltage over R519 = 0,5 volt R521 = 0,7 volt / R522 = 0,7 volt R520 = 0,50 volt ..78M12 is also ok .. 1st thing i checked when i opened :-)

author: oldway
author_rank: Super Contributor
timestamp: December 27, 2016, 09:42:14 pm
content: Check if you don't have a NEGATIVE input voltage on R559.....in this case, C501 would be reverse biased and will leak for sure, applying a negative input voltage to Q501.All the amplifier would than be OK and this could explain the -19V on the emitters of Q1 and Q3 with all the components checked as OK.

author: on4top
author_rank: Regular Contributor
timestamp: December 27, 2016, 10:14:23 pm
content: i have 0,9 volt on both Resistors on the pin connected to C 501 & 502 ( r559 & r560 )on the other side of resistor i have 6,8 volt ( measured to gnd )ps : C501 is the working side for now .. C502 is the bad side of the amp .als since i removed the resistor en the relay works . voltage on emittors has going up to -29V ...R515 has only 0,05 volt across ..R516 has 24,5 V across !! ( non working side )Q501 & Q515 have an emitor/collector voltage of +/- 45 voltQ502 & Q516 have an emitor/collector voltage of +/- 30 volt .

author: mzacharias
author_rank: Frequent Contributor
timestamp: December 28, 2016, 05:38:23 pm
content: can we get some voltage readings across critical resistors such as R520(R519) R521(R522) R563(R564) etc?

author: on4top
author_rank: Regular Contributor
timestamp: December 28, 2016, 07:40:31 pm
content: R520 = 0,60VR519 = 0,56VR521 = 0,84VR522 = 0,89VR563 = 0,934 VR564 = 0,33 V

author: mzacharias
author_rank: Frequent Contributor
timestamp: December 28, 2016, 10:42:41 pm
content: I would suggest replacing the differential transistor pair on the input portion of that channel.For confirmation, you can swap the pairs from one channel to the other. If the symptom moves to the other channel, diagnosis is confirmed.

author: on4top
author_rank: Regular Contributor
timestamp: December 28, 2016, 11:58:00 pm
content: Q501 & Q515 swap with Q502 & 516 right ?

author: mzacharias
author_rank: Frequent Contributor
timestamp: December 29, 2016, 04:44:54 pm
content: Quote from: on4top on December 28, 2016, 11:58:00 pmYes - that's them.

author: on4top
author_rank: Regular Contributor
timestamp: December 29, 2016, 05:03:04 pm
content: done this .. no change .working channel still works .did the same for Q510/Q512 with Q511/Q09.so all these transistors are fine .

author: mzacharias
author_rank: Frequent Contributor
timestamp: December 29, 2016, 11:12:42 pm
content: Well then try Q505, 506, 507, 508. Next up would be other less likely higher value resistors. There is also a low frequency rolloff capacitor C511 / C512, if I have not already suggested. Leakage here can cause offsets but usually full rail or drifting around in value.

author: on4top
author_rank: Regular Contributor
timestamp: December 30, 2016, 01:36:41 am
content: swapping Q507 & Q508 i think did the trick ..Left channel now seems to work ..have to unsollder r557 now.. ( to override dc protection ) DC voltage is now on the Right channel ... with Q507 removedr558 is back in place .. so dc is gone on the left channel now ..now source a 2SC2705 or equivalent ...

author: KhronX
author_rank: Frequent Contributor
timestamp: December 30, 2016, 01:47:13 am
content: http://www.ebay.co.uk/sch/i.html?_from=R40&_sacat=0&_nkw=2SC2705&LH_PrefLoc=3&_sop=15and/orhttp://www.ebay.de/sch/i.html?_from=R40&_sacat=0&_nkw=2SC2705&LH_PrefLoc=3&_sop=15&_clu=2&_fcid=70&_localstpos&_stpos&gbr=1

author: on4top
author_rank: Regular Contributor
timestamp: December 30, 2016, 01:49:02 am
content: yep that will probably the simpelstaltough i hate waiting .. want this thing of my workbench before 2017thanks for al the hints ... now i'm thinking why it's gone bad .. AND when i test on transitor tested it seems ok ..

author: mzacharias
author_rank: Frequent Contributor
timestamp: December 30, 2016, 01:58:01 am
content: Wish I'd thought exactly of this sooner - I've seen many 2705's and 1145's bad, often noisy, often causing offsets. I used to buy them 10 to 20 at a time.

author: on4top
author_rank: Regular Contributor
timestamp: December 30, 2016, 02:02:04 am
content: Yep i probably wil buy some spares and replace them in both channels .Transitor tester did say some higher values i compared both of them .. so must me some difference ..Not easy the find the bad one ... shorts are easyer

author: KhronX
author_rank: Frequent Contributor
timestamp: December 30, 2016, 10:29:04 am
content: Perhaps some BD139's might be easier to find locally? They should be "close enough", and are some of the most widespread "medium power" NPN's in Europe, i thinkOr maybe MJE340's...

author: on4top
author_rank: Regular Contributor
timestamp: December 30, 2016, 11:18:17 am
content: i got bd249 .. but that's tooo beefybd139 i should find in someones junk box

author: KhronX
author_rank: Frequent Contributor
timestamp: December 30, 2016, 11:37:50 am
content: To be on the safe side (and i'm a bit "OCD" about symmetry), i'd replace both of them (ie. on both channels).Since mzacharias said they often fail, might as well save yourself some headaches down the line

author: on4top
author_rank: Regular Contributor
timestamp: December 30, 2016, 11:39:02 am
content: yep that is the plan ..wil order some now .. just want a proof of concept now en see both channels workingwill have to wait until next week ..

author: mzacharias
author_rank: Frequent Contributor
timestamp: December 30, 2016, 02:06:57 pm
content: Late '90s Pioneer stereo and surround receivers were rife with the things. Noisy channels, protection issues, etc. Due to difficulty for access to replace them, it was standard to replace all of them in a given unit. A five-channel model might get 20 transistors replaced in total, mainly to prevent re-do's and similar future problems. Seems the transistors were somewhat "stressed" over time by circuit voltage etc. I asked our Pioneer service rep if there was any recommended upgrades - there were none. Guess they just "didn't care" to re-engineer or research proper substitutes.

author: KhronX
author_rank: Frequent Contributor
timestamp: December 30, 2016, 02:40:01 pm
content: Even though those long TO92 package are rated for 1W usually, it's still a bit of a stretch, in VAS duties. TO126-packaged ones are more usually seen (in more "proper" designs)

author: on4top
author_rank: Regular Contributor
timestamp: December 31, 2016, 04:14:56 pm
content: seems i was lucky yesterday ..local electronics store had 2 pairs of them on stock .. 2,40euro a piece ..swapped them yesterday night ..https://www.youtube.com/watch?v=8iUOQ0PnjG8&feature=youtu.beNow stress testing ...Thanks everyone here on eevbog forum for your input ! I learned a lot with this repair ..Happy new year !

author: mzacharias
author_rank: Frequent Contributor
timestamp: December 31, 2016, 08:21:21 pm
content: Quote from: KhronX on December 30, 2016, 02:40:01 pmGlad that worked out for you!