Restoring & modding a Marantz 3800

To begin, you need to pull the following components:

Part #s Q211 & 212, C233, 234, 237 & 238, and R253 & 254. You also need to remove C239 and 241. Replace those two bypass caps with some .22uf Panasonic ECQ films. (Digikey part # P4667-ND) Since the voltage being supplied to the chip was only around 16.8 volts in my unit, i didn't replace the voltage dropping resistors (R267 & 268). But if in your 3800 you are getting much more than 17 V supplied, you should probably increase the value of these resistors. (The existing value is 10 ohms, so going up to as little as 47 ohms might be all it'd take.) I have been told it is not advisable to let an op-amp run very close to it's max operating voltage, if possible. Next, pull the fourteen pin chip socket and replace it with the eight pin socket.

Now the jumpers. Again, i made mine from leftover leads trimmed from the new capacitors.

Pins to jump are as follows:
Pin 5 to pin 3 via the empty pad for R253. This jumper must have heat shrink on it since it is so close to the new socket base. I put heat shrink on most of the other jumpers as well, but only this one must have it i feel.
Pin 6 to pin 2 via the empty pad of C237
Pin 7 to pin 4 via the empty pad of C233
Pin 8 to pin 12 via the empty pad for C238
Pin 9 to pin 11 via the empty pad for R254.

The jumpers are flush with the board and are bent/angled a bit to not interfere with each other and the new chip socket. None cross over. Picture one shows the emptied PCB, picture two shows the jumpers installed and picture three shows the new IC socket installed. Once everything is in place and cleaned up, power up and test to see of the right voltage is on the correct pin locations. If you put everything together right, it should be. If all is well, power down, instal the new op-amp and power back up. Pictures four & five show the 2134 in place and how everything looks. Now you are ready to calibrate.
 

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Section 7: Calibration and preliminary tests

My first observations of the rebuilt 3800 with the new pre amp IC, were now very promising. It showed no instability that i could test for with the limits of my signal generator. (Up to 600khz.) It also handled a 1khz square wave with no overshoot or ringing, only starting to develop a step when i passed 2/3 full volume. (Input was .5V on that square wave. By the way, don't do this with an amp or you'll cook it.) All the pots and sliders were also dead quiet now. Absolutely no drop outs through their full range. Switching from tape 1 to 2, or through the various Dolby settings was also quiet and no longer intermittent. I went through all the function tests as outlined through the service manual, and confirmed everything to be working at, or within expected ranges. There really isn't much that a user can adjust in the 3800, except for the Dolby VU meter and test tone levels. Finding the service manual's description to not be that clear, i asked Catrafter for his method. Below is the procedure he told me to use:

To set the 400Hz tone gen:
Set the controls as per 3B (page 2-8) in service manual.
Turn the unit on.
Connect an AC voltmeter to one of the tape out jacks on the rear panel.
Set the Dolby switch to Record 1 and press the 400Hz switch in.
Adjust R702 for 580 mV, which is .580 Volts on the meter.
R702 is the lower pot accessible through a hole behind the power switch when looking in the right side of the unit.

Leave the Dolby switch in Rec. 1 and the 400Hz switch in.
Connect a set of RCA jumpers from Tape 2 out to Tape 1 in. Set the source switch to Tape 1, set Play level pots to midrange (12 0'clock).
Adjust R706 (above R702) through the top hole for 0 dB on the meter. Done!


After finishing up the Dolby calibration, i connected a tuner to the unit and left it running for a day to allow the new parts some burn in time. No issues with parts getting hot were found during this test either. (The voltage regulator will get warm of course.) I ran some more tests with sine wave inputs and according to my scope, what i put in is what i got out. Very clean signals. After this, i decided to button the unit up and put it back in the rig for some listening tests. But first i needed to finish cleaning all the exterior parts. I used Windex on the faceplate and buttons/knobs, and then gave all aluminum parts a good polishing with Meguiers Cleaner Wax. I also glued back in three of the grommets that protect the buttons from grinding against the metal faceplate. One of these was missing, and i thank Aker Robisme again, for sending me a replacement. I also replaced the worn out protective felt that keeps dust out of the sliders. Being unable to find felt thin enough for the job, i got a hold of some bias tape from the fabric store and used that instead. I cut it to fit and contact cemented it down on top of the existing felt. (pic 1 shows the left side glued in and the right side still original.)

With an exacto knife, i slid through the opening of the slots to cut a path through the new fabric for the sliders. I also put a new piece of double-sided tape over the VU meter wires and stuck a new piece of foam on. After that, i put all the buttons back on and bolted the faceplate into place. (pic 2) Attach the knobs and screw the main cover back on and it is done. (pic 3)
 

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Section 8: Listening tests

I'm not very good at describing stuff like this, but i'll give it a try. My initial reaction to the new sound of my 3800 was WOW. Most noticeable to me was the absolutely silent background. Previously it always had a hissy noise floor, a bit like listening to a blank cassette tape. But now, even at max volume, there is silence. I just kept rotating the volume pot listening for static or other issues, none. None from the balance slider, none from the tone sliders, just beautiful silence. (I’m still in love with that fact.) First music input was from the CD player, very nice. I did feel the bass was a bit weak, but then i pushed the loudness switch in, and it was much better. Switching it in did not add any boomyness i could detect. I'd say the loudness was doing exactly what it's supposed to, make things sound equal but not exaggerated. (In case anyone is wondering, i was listening with headphones.) Overall the music sounded unhindered and clear. The high frequencies were no longer fuzzy and indistinct. Good sound stage presentation as well. I found i could hear little sounds i had not noticed before, like the horn players breathing in, or a chair creaking. I used to keep the tone sliders in that smiley face shape, but at no point during my tests did i feel the need to do this. When i did, it just sounded exaggerated, but not any better. So for the first time, i am running my rig with the tone controls flat. Input from the cassette deck and reel to reel was also clear and very good sounding. Switching between tape decks was smooth and produced no pops or intermittent channels. All Dolby selections were also quiet. What about the phono section? Initially i hooked up the only working table i had, a crappy plastic RCA unit. I could immediately tell i was listening to a low end piece. It was bad enough that i cut short that test, until i could get the Technics hooked up. Once i got it in place, MUCH better. It was just as clear and nice as any of the other inputs i tried. Only a faint bit of hiss when the volume is cranked all the way to max.

It's been about two months now, (as of Dec. 2012) since i finished this project. I'm no music analyst or audiophile, but to me it is wonderful sounding. I feel it does what a pre amp is supposed to, control the sound but not hinder it. While my memory of the old is certainly not perfect, i can definitely tell a big difference was made after the restoration. Everything just sounds better now, even the tuner. I am curious to know how much of the difference in sound lies in what i did, or how the unit is supposed to sound to begin with. However, i'm not too inclined to buy another just to know this. I've got plenty of other projects awaiting my attention. But one thing i do know, as new pieces come in, and my system continues to improve, i think this 3800 will be hanging around for a while. And even if i do surpass it, i don't think i'll be letting it go, just in case. Of course, purists may cry bloody murder after reading what i have done. But to twist what JG Wentworth says, "It's your stuff, use it as you see fit!"

I hope this thread proves useful to someone. I am glad to finally be able to give back to a great community that has given so much to me. Without you guys, this unit would probably be sitting in a closet dead. Thanks again to all the Akers who have helped me in this process. Good day all and happy listening!

P.S. Enjoy the pics of the finished unit hanging out in my rig.
 

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Very nice job! I have a 3600 preamp that I really like. Its original but still sounds good with no noise. I had it checked out a few months ago thinking it had a problem that turned out to be the amp. All tests came back within specs for the most part. However the highs are starting to role off a bit now. I'm currently using my 3200. My wife was cleaning and my 3600 wound up with a 3 inch scratch across the face. I'm currently looking for a new face plate. When I find one I'll do a complete referb. On it. Thanks for sharing. Again, nice work!
 
Amazing restoration and write up. Thanks for sharing the journey. The silver dip trick alone was worth the read. AK continues to amaze me with the depth of knowledge presented.
:thmbsp:
 
WOW! . . . . outstanding, detailed work . . . all the things I would like to do for my 3250 pre . . . I have done some R&R work on gear before, most recently the power switches on the NAD 2140, 3140, 4020A which are Alps units; a pain to get apart but after doing one, the others were ez . . . but I dunno 'bout a complete redo as done here; my confidence just ain't there yet! . . . mebbe the wrong forum, but would this be a $500 job at a shop? . . .
 
Thanks for the compliments guys. Anyone else who has reworked one of these, feel free to post your experiences and tips. I'd like to see what you did.
 
I acquired one of these 3800's, a 3300 preamp, a 4000 quad preamp, the quad adapter, an Advent 100 Dolby noise reduction unit and a late 60's sitar a few years ago. I am finally about to hook it up and see how it does. I am planning on using this as my main unit in my stereo. Your information is awesome, although I hope, at least for now, not to need it. I will post again after I have my system hooked up.
 
Bringing this thread back-- my 3800's UA749PC I believe is the problem. I took a gambke and spent $10 on one of the Korean IC's listed on eBay. Has anyone else had any experience with them? Hoping it's not junk. Be so much easier to plug a new one in rather than go thru the above steps.
 
I am in the process of restoring a 3800 myself and purchased 2 of that chip though Little Diode (Ebay).
I haven't gotten around to finishing the 3800 as the weather has been great but when it turns and I finish up I will let you know how it works,.
 
I got my UA749PC today from China (actually it's stamped from Korea), installed it and it appears to work! I am still experiencing an output issue - the left channel is not as loud as the right. I just fixed that exact problem on my Marantz 3300 Preamp. Capacitor C412. An electrolytic 2.2MFD, 40V was shorted on the TIMES TEN board. So, I'll start there after I check & clean all board contacts/plug ins.
 
That's great news that it works.
I will finish up with my 3800 this weekend as the weather is suppose to be a dud.

But then something I didn't expect to happen did:<) .
Just acquired unexpectedly 510m / 3800 / 150 ,soooo...
Now I have (2) 3800s LOL.
Looks like I will have to part with one as well as a 510 and a 120b also in my "collection" LOL.

It a sickness I know LOL


I got my UA749PC today from China (actually it's stamped from Korea), installed it and it appears to work! I am still experiencing an output issue - the left channel is not as loud as the right. I just fixed that exact problem on my Marantz 3300 Preamp. Capacitor C412. An electrolytic 2.2MFD, 40V was shorted on the TIMES TEN board. So, I'll start there after I check & clean all board contacts/plug ins.
 
Appreciate the skill, knowledge and effort put into this restoration. Will serve 3800 owners well into the future who want to tackle this intimidating piece.
 
Just got my 3800 buttoned up.
The ua749pc chip works perfectly
Recapped the whole unit as well.
I will say it took some time to get though it as I took my time.
I have to thank all the techs that contribute to this wonderful forum.
I have gained a tremendous amount of knowledge hanging around here.
All I can say is wow what a great preamp. A very precise and open sound stage. The unit was a local purchase in pristine condition cosmetically and is a keeper.
 
The 3800's Service Manual is rather poor in comparison to the 3300. I'm experiencing heavy distortion & lower output volume on the left channel. Also when the 400Hz tone button is depressed I get serious motorboating. ( I think that's the correct term) The right is performing perfectly. In the 3300 manual in the Trouble Analysis section, it gives specific parts to check for the specific problem. It also differentiates between Left & Right w/ parentheses. Wonder why this was not done for the 3800? I did print out an 18" x 24" of the Preamp Schematic & am going to go through the Times Ten Amplifier and the 400Hz tone Oscillator for my first suspects. Any guidance is much appreciated.

EDIT: I stand corrected - NOTE 5 - Odd numbers for Left.
 
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