I hate to say these power booster things did not have the best of sound when new out of the box. Does it have line level inputs or meant to be driven by a non-bridged car radio?
The MOSPEC output transistor sticks out like a sore thumb in the middle of its Hitachi siblings...
they all run somewhat equal as output goes except the far right set that read 8 v on one side and 7 v on the other... That set sticks out at this point. I look for uniformity in my meter readings so them 2 on the end there.... I THINK I am having a degraded single channel INPUT side.... Both channels work, one is slightly distorted and somewhat weaker than the other side. EQ sliders appear to operate OK on both sides. Not TOO concerned in regards to FULL BLOWN LONG RUN operation at this point.... just getting it operating again and LEARN from this experience.... then on to something else. THANKS for chiming in! BDBD/2022
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ONLY speaker level COMMON GROUND 5 watt input, NO RCA level inputs, yeah... I am 63 years old and I was an early (1973) adopter of them little BOXES for yer stereo... LONG ago they were all that was available so... as SPEAKERS back then, 10 watts made em MOVE.... efficient. So systems were louder than folks get, back in them daze. This particular one is a MUNTZ. I in my decades of car stereo experience have only seen ONE other MUNTZ EQ, a different model with a METER on its front face. RARE RELIC from the MADMAN..... I used to work at MUNTZ ELECTRONICS here in Honolulu, mid/late 80's... 13 cars a day.... days... It WILL OPERATE and SOUND GOOD... I dont give up. BDBD/2022
the Turtle won the race.... I have nothing BUT time Perry.... waiting for the Grim Reaper here so... no rush, instead an EXERCISE... I will use my Degree for this schematic, exercise my brain and learn from doing so. Perhaps a pencil drawing would help me compartmentalize this layout, I get that. My PENCIL WORK in Art Class was among the worst. In a BOX of HAMMERS, I am the SLEDGE. BIG... hands... THAT BEING SAID, I purchased a CLASS D "SPL GORILLA 2400 watt" amplifier... 35 bucks on ebay, It hits PROTECTION upon power up and my LIGHTBULB lights up so.... NEXT!!!!.... I start to apply what I have learned from your SITE on something more along them lines. Thanks again for your inspiration... FUN FUN FUN...BDBD/2022
upon first examination it appears that BOTH rectifiers died as well as a SINGLE output transistor. So far thats what my meter tells me. The MAIN POWER INPUT is not shorted, no BEEP when i checked for that. I am sure once ya POWER IT UP, them power inputs will short as they LIT my headlight nice and bright. Time to buy some more Transistor stuffs.... Keep ya posted, BDBD/2022
Ahhhh maybe rectifiers are OK... I get a short BEEP but no real short to the center leg on either outer legs, which do short as you mention as a result of the transformer they are attached to. OK... rectifiers appear to be OK, ONE output transistor is surely bad and I am probing the POWER SUPPLY transistors and some seem to have a short between the center leg and one outer leg. Only a couple, the rest are NOT shorting between any legs. I will triple check your SITE and recheck them transistors a few more times before I warm up the soldering iron. Hope its only transistors..LOL... BDBD/2022
Likely 3 bad output transistors... the HOT side of the amp it appears as theres a temperature heat switch on that side but not on the other. I will pull these and see what I can find online... ONE QUESTION... do I change all 3 OR all 6.... Hmmmmm..... BOTH SIDES. One side appears fine, other side has some shorted transistors for sure. OK.... BDBD/2022
Of course, you have to replace all transistors that are actually defective. Replacing the others may be a gamble. Sometimes, the newer transistors (even the same part number) are not exact matches and can cause problems. I'd suggest replacing only the defective and then, after it's working perfectly, you can replace the others.
ahhhhhhh maybe just ONE output transistor... I PULLED the OBVIOUS bad one and then tested them others and NOW they are OK... no shorts. I BET this cheapo amp has a mismatched transistor set from the factory. Thats what makes better products is that MATCHING of components. CHEAPO.... they toss whatever they have in there and if it passes the test its out the door.... Premature blow up, like a ticking time bomb. WELL who am I to bump heads with them TECHS...LOL...... SO I gonna order ONE FB31N200 transistor and install it in that spot and see if it powers up.... if it does then check for HEAT.... no heat.... HAPPY AMP.... OR... buy a whole set of 6... These are sorta difficult to remove from the board I have found REALLY just want to get this thing to operate.... CHEAPO Learning Experience.. Uggggg.... Just another day.... BDBD/2022
Thank You for your advice Perry... I hope only ONE transistor will do it.... Will keep yas posted. WAITING for even MORE capicitors in the mail in regards to the MUNTZ EQ. Soon it will WORK!!!! Determined here.... BDBD/2022
I cannot figure out the Mylar Capacitors in there, they say "YAMATO", 50k and theres a .1
Cant seem to find a conversion chart that equates to these new Caps I bought. Uggggggggg..... I want to change out them caps but cant figure out what to replace em with.
Fun Fun Fun.... BDBD/2022
Cant seem to find a conversion chart that equates to these new Caps I bought. Uggggggggg..... I want to change out them caps but cant figure out what to replace em with.
Fun Fun Fun.... BDBD/2022
The '50' may be a voltage rating. The 'k' could mean 10% tolerance. The '0.1' could be 0.1uf.
Hmmmmm interesting... These YAMATO caps are the SAME VALUE as them other ones I replaced already, but THEY had the NUMBERS on them. These YAMATO caps I have found are used a lot in guitars etc. Perhaps these YAMATO caps are "audio grade"... I wonder WHY they used "generic" caps near the output transistors (them ones with visible cracks) and these YAMATO caps in the pre amp stage. There must be a reason. WELL, i replaced all them YAMATO caps, 2 did not even register on my meter.... two are close to spec, i changed all 4. Seemed to make a SMALL difference BUT theres still a detectable DISTORTION on one channel. SEEMS to be working better upon startup but soon degrades.... I have CERAMIC caps on order so they will be next. That would be ALL the caps replaced with newer ones. MY FIRST total RECAP.... transistor swaps... One of these days It will work fine on both channels. SOON. Keep yas posted. BDBD/2022
ALRIGHT...... Managed to replace ALL the capacitors. Each and every time I changed something there was IMPROVEMENT in sound BUT... STILL one side DISTORTED.... Ugggggggg..... Maybe RESISTORS?.... I went and checked all them resistors and they all seem to measure OK.... Hmmmmmm SO... PROBE A MANIA. ... as it turns out a POWER TRANSISTOR was showing a strange reading in comparison to them others so.... MORE TESTING.... I THINK I FOUND IT... Transistor SEEMED to be working IN CIRCUIT but upon removing power there was a OPEN LUG... Not that obvious BUT upon REMOVAL I found it to be BAD. Bad transistor right next to that one that was OBVIOUSLY blown. SO... ORDER another transistor and HOPE for RELIEF........ I been at this MUNTZ now for over a month..... GREAT LEARNING EXPERIENCE. I am getting much better at soldering etc. Cant Wait till the transistor arrives and see...... I HOPE i can finally get this EQ to operate and sound good..... I have the GORILLA Class D amp transistor on its way tomorrow so.... More to do. I WILL get this done. BDBD/2022
so.... I have perhaps a solid WEEK of TOIL invested... about 50 bucks for the EQ and PARTS... Guessing I should start the BIDDING at $2500.00... LOL.... I gonna BE RICH fixing amplifiers!!!! YeeeeeHaaaaa..... Uggggggggg..... This RELIC might even SELL for that amount. Hey Mr MUNTZ JET owner.... LOOKY what I HAVE.... a real working MUNTZ EQUALIZER AMPLIFIER from 1977, all new CAPS and transistor upgrades and FULLY OPERATIONAL in 2022..... ONLY $2500.00 including taxes and shipping. I seriously think I have OVER a week of toil in this... "learning experience". SOON... IT LIVES!!!!!!! BDBD/2022
Don't hear that name often, I'm restoring a 1966 Muntz round screen color tv set at the moment. Chassis is RCA, but the cabinet was pure madman Muntz. No screws, just scrap wood held together entirely with glue lol.
Screws are EXPENSIVE... HERE, use this can of GLUE... EVEN THE CABINETS were "Muntzed"...LOL Great story...