Another stereo.

Recently was offered this hi-fi by a work colleague. Garage clear-out, it had been sat in there for years.

Marantz MR1155

It’s a Marantz MR1155, from the early malaise years of cost-cutting and design setbacks. It also didn’t work. Power was applied before I got it, and apparently it went click and made a bit of a crackle.
Sure enough, it would power up and come out of protect, but not much else happened. Evidently the protect circuit was not detecting a particular problem so that was kinda okayish.

dust werewolves

With the lid removed, the contents of the device appeared to be mostly lint. Yuk. That has to be the worst hifi I’ve owned yet in terms of dirt.

clean

Thankfully it all cleaned up nicely.

stripped down faceplate

Pulled the front off after work, removed all the buttons (they had gone green and fusty) and brought it all home to clean up. Judicious application of drill and polishing mop got it looking respectable again.

shiny

Not perfect by any means but definitely better.

lid

Cleaned up and put the lid back on. Fairly respectable.

in bits again

Brought it all home and started to poke about. Pulled up the manual off HifiEngine and set about looking for the cause of no audio. Powered it up, the main amp voltages were pretty much in spec, but the FM/AM/Phono/Preamp board was dead, with hardly any voltage. Bypassed the preamp board and fed the power amp board directly- presto, greeted with slightly clipped but definitely OK audio. The expensive amplifier modules are still OK.

caps

Ordered the full replacement of electrolytic caps to shotgun all the boards. Over the course of a couple days I replaced everything. Still no voltages, so I replaced the transistors that control the voltage and protect circuit.. nothing much. Further troubleshooting found the 14V Zener to be almost a dead short over 0.3V so I went to desolder it and it cracked into 2 pieces. With it removed, bringing up the variac got the voltages to rise. There’s the problem then. Ordered a couple 14V Zeners and whilst in town stopped at Radio Shack and picked up a couple 12V ones to see if that would get it to come to life:

alive!

Sure enough. Not very good but operational. Went to tune the FM because it was not working very well at all post e-cap replacement. Broke the discriminator tuning slug (even using a fiberglass tool of the correct size) so pulled that out and took it to bits. Ordered a couple replacement cores, so need to wait until it’s all back together before readjusting.

10.7MHz transformer

Go figure. It had to break..

Reflective! Also, frosty.

Bought a mirror from a gentleman in Canada.

mirror

Bottom one (old) being held up. Sunshine and humidity made all the silver fall off. The new one looks new by comparison.

Also moved the car and mowed because the grass is growing fast this season.

grass

That’s 4 days’ worth of grass growing around here.

frozen

Also the new heater element arrived for the freezer. Not a day too soon, it was beginning to freeze up. That again was 4 days’ of ice.

Brake bias valve

I finally decided to disregard the service manual and remove the brake safety/bias valve assembly as bleeding the brakes resulted in the pedal becoming solid halfway down its travel and not really doing much. Bought an open ended ring spanner (flare nut wrench) and some PlusGas releasing agent. Sprayed it all up and let it sit before attacking it with the wrench.

wrench

After a while it was all undone.

valve gone

Offending item out. It’s not very big, but it’s milled from a chunk of aluminum.

grubby

Looking into it showed that it was kinda grubby. Undid the safety shuttle valve assembly.

end cap

Yeah, that’s meant to be very clean inside there. It wasn’t.

shuttle valve

The shuttle valve end. It was firmly stuck in position, that’ll be why the brakes didn’t want to bleed properly, then.

piston

Had to hammer it out. It was covered in crusty, solidified old brake fluid. Cleaned it up. Surprisingly the seals are still good.

shuttle done

With the shuttle valve cleaned out, I undid the bias valve assemblies, which were similarly dirty but at least not stuck (too much) and cleaned them out.

all clean

Reassembled it all and put it back in the car. I now need to bleed the system. Hopefully now it’ll be good.

Speaker grille redux

Finally, I added another coat of stain to the grille face of the speaker that I rebuilt.

drying grille

Sat on the cardboard box in the back of the truck to dry in the sunshine. Plank of plywood next to it for the PSU project I’ve been building.

Once the stain had soaked in it got buffed off and left in the sun a while, then I gave it a coat of Tung oil and let that set.

cloth

Measured and cut the cloth. Stretched and stapled it into place on the spacers.

fixed grille

Added the badge back on and put it in place. Looks sharp!

Multi-cap can

Had a bit of spare time and inclination today so I took all the connections off the back of the McIntosh after labeling the wires. That’s a task in itself.
Removed the old multi-cap can. Took to the base of it with the Dremel. I had wanted to retain the original look of the capacitor as the top of it sticks through the chassis. The old brown heat marks show the point where it shows. The Dremel cut is well below the visible line.

dermelled

Mallory’s finest. Still in surprisingly good physical shape.

can dissected

Cleaned the dregs of tar out of the case after softening it a bit in boiling water.

tarpit

Removed the old capacitor wad. Four new caps to fit inside. It would appear Nichicon listened to the classic audio crowd because these are common values and voltages the the era, designed to fit inside old cans easily.

new bits

Fitted the caps all in place. They fit nicely. Actually over the spec of the originals on voltage and temperature. They should last.

newcaps

Had to drill the base to pull the leads through. Kept the original markings intact.

square triangle semicircle

Glued back together it looks nice. Gave it a bit of a buff up with a bit of metal polish.

restuffed

Looks neat back in the chassis. Sitting listening to it now and it’s running happily.

Much more brakes

grunge

Mmmmm.

Weather today was nice enough and I had the day off so I set up on the ramps and pulled my brakes to bits.

pot of gold

Old stuff to come out wasn’t horrible but I’ve certainly seen better.

master cylinder

New master cylinder.

clean fluid

New fluid. Certainly better than the old. Tried vacuum bleeding the system but ended up with an infinite supply of bubbles and not much fluid so called SWMBO in to shove on the pedal a bit.

Net result is brakes, but I did notice that the back section of the reservoir would never empty when bleeding, only the front. Pedal is better and the brakes are fairly sharp but now it feels like you hit the sliding shuttle inside the master cylinder and it’ll go no further. I think the bias valve is stuck one way and only working the system on half of the, er, system. The other half of the system then just making pressure against the valve and it going nowhere.

I’ll have to get a split-O 12mm to try and get that undone- 6 pipes that have never been undone that are steel into aluminium. That bodes.

I might try and source a replacement first.. not sure if it’s a Bendix part or Renault or none of the above.

Square one. I hate brakes.

Matchmaking

I recapped an old Dell power supply, as it has some useful voltages (-12, +12, +5, +3.3) and was more than enough powerful (160W) for most of the projects I do. Added a small load to the +5 rail and the voltages stabilised, that’s the light bulb.. spent a bit of time and built up matching circuit on Veroboard.

messy

Initial testing was good, so tidied things up a little.

board

Set about measuring transistors to see the Vbe of each. Matching at 72F to within 2mV.

measuring

Did 100 of them, they are surprisingly close (all within about 5mV) so I have more matched and/or similar pairs than I thought! That’s good, means all the transistors installed can be identical.

McIntosh recap

Along with the parts for the Marantz, I bought a set of parts to make a transistor matching circuit. I bought 100 of each NPN and PNP silicon to match up accurately, as that’s what the spec calls for on the amplifier boards.

recap preamp

I recapped the preamp boards first. All ultra-low impedance capacitors, as per the original spec, though these are aluminum rather than tantalum.

regulator

Redid the regulator/phase-shift board.

compare

As a comparison, I put the power amp boards side by side, the left one done, the right one yet to be.

power amps done

As if by magic, the power amp boards are recapped. I bought some very tall and thin caps to restuff the multi-cap (4 capacitors in one can) because it growls a bit on power-up. I want to keep the appearance of the original can because it’s a prominent feature of the top of the case when you look at the chassis. It’s polished aluminum. That’s up next. I’m going to save up and get the main filter caps at a later date because they are rather expensive ($25 each).

AM Stereo

Back in 2013 I picked up as part of a package deal a Marantz SR840 receiver. I got it for nothing because “it didn’t work” and “if you feel like you want to fix it, go for it”.

sr840

Sure thing! The above picture is from after a thorough clean. It was grimy and horrible. Powered up but didn’t do much more than blink lights and show it was tuning to a radio station.
I’d had a bit of a dig about, found by bypassing the preamp and feeding the power amp it would make fairly acceptable noises. The preamp did not put out but the radio board had output. It was very one-sided when probed with my oscilloscope, and sounded distorted.
I tried to poke about for voltages but without a schematic I hit a dead end. I hunted about for a service manual but found none. It got shelved.

I was thinking about it the other day, and decided to go on the search again for a service manual. In 2014 someone put up a good scanned copy for sale at Analog Alley for $16. Fifteen minutes of work later I determined the cause- no -15V on the preamplifier.

schematic

I ordered some bits and bobs. There’s a small regulator chip for the +15 rail, I’m guessing there was no -15V integrated regulator available at the time so a PNP transistor, bleed resistor, couple of capacitors and a Zener diode formed a -15V regulated supply.

R443

I managed to make one of the resistors smoke up accidentally on the radio board when I disconnected the -15V supply to see if it would come up with no load.

new resistor

Replaced that, bought some new parts.

broken bits

Removed the power regulator circuit and replaced it with new. The 100uF capacitor had gone short circuit and had taken the Zener and transistor with it. The resistor was a bit high due to the current draw so was replaced also.

new

All the new bits in on the board. The entire chassis is packed quite tightly.

alive

Net result was to be presented with stereo FM! It worked for about fifteen minutes then overheated a capacitor in the power supply… the display and LED’s went all funny then it shut off. It came back up a short while later after it had cooled off, so it just needs all the electrolytic caps replacing. It’s kinda worth it for the stereo AM.. the tuner on it is actually pretty good. It’s being buttoned up for now, but I’m happy in the knowledge there’s nothing drastically wrong with it.

1866 for 6100

I bought a new set of #1866 bulbs for the McIntosh, as most of them had burned that illuminated the front panel.

panel off

The old foam surround going around the buttons had dried out and was turning to dust.

vacuum

Too the vacuum cleaner to it, it all just disintegrated and fell off.

peel

That left just the original sticky backing, which peeled off.

foam

A new length of foam that I’d bought for things like this came into play.

new foam

Created a new surround for the buttons following the original pattern.

hot

The original bulbs run quite hot. The speaker ones were not even brightness, so I fought for half an hour getting them out.

nice

All buttoned up, new bulbs fitted. I think once I get a new face for it, the incandescents will be replaced by LED equivalents. This is mostly just a hold-over because it was annoying me not being lit up.