Category Archives: Marantz MR1155

Redux of the last few months.

It’s been a slow few months with little to report. I’ve lost faith in a few things, with a couple problems and issues with projects that had me baffled and I kinda lost interest in them.

However, things have picked up a little and I’ve gone back to the troubled projects or made some headway.

I bought some replacement tuning slugs for the Marantz receiver. They aren’t 100% the same permeability but they are the correct screw thread.

slugs

Replaced them in the transformer after carefully breaking the old ones up and getting them out of the core. Now I know what they feel like, the old ones were broken before I even started- the lack of decent radio reception certainly points to that.

radio waves

I got all set up and the thing refused to tune well. I could get a couple of strong local stations but the tuning meter and tune indicator would not light up, and those are partially controlled by the transformer. I connected my oscilloscope to the input side of the transformer to check the waveform was not distorted and all of a sudden, LOUD radio, strong signal! Uh.. yeah ok. Reflowed the solder, no effect.. touched the oscilloscope probe to the transformer again gently, and bingo. Strong signal. Touched my finger to it.. improvement. Okay, so it’s a capacitance issue. Experimented and ended up with a 10pF ceramic cap across the terminals to bolster the transformer. Now the selectivity and sensitivity are great. It’s right now the best radio I have in the house for FM stereo.

Carried on with it but now it keeps tripping out into protect. I’ve troubleshot the protect circuit, one of the other boards must have a leaky cap on it somewhere. I need to pull the boards power supplies off one by one and see what fixes it.

Next up, refinished the floors at the house. Edging strip all done in the kitchen:

kitchen skirting board

Finished up in the utility room, flooring strip and the paneling done:

utility room door

Finished up the cabinet around the water heater:

water heater

Pulled the stove to bits and thoroughly cleaned it, the glass particularly was vile.

stove

Finished the floor edge strip in the living room, split the flooring between the two rooms where it was buckling and added a divider to allow for expansion.

living room floor

Rented a floor sanding machine and sanded the floors back, as previously they had looked OK, but having painted the walls and tidied up they were the least well-finished parts of the room.

floor sander

Solid cypress flooring. Smelled real nice when lain bare.

floor stripped

A few coats of polyurethane clear varnish later:

shiny

Looking much better. Also, picked up a nice Holophane light fitting on clearance for $4 at Home Depot. Fitted an LED light to it that has 4 segments inside, looks rather like a standard light bulb:

light fitting

Been troubleshooting the brakes on the car for a while. Stumbled across a post on a Ford Explorer forum with the same symptoms as mine. Turned out to be a faulty brake booster servo. I’m going to vacuum test mine this afternoon, have my MityVac for the purpose (shown here with brake bleeding catch-can fitted):

MityVac

Also picked up a GTE Palco payphone, which has gone into service here at the house, with the requirement for coin removed.

GTE Palco payphone

I repaired a little Realistic PA amplifier that got struck by lightning, and built a cardboard speaker to test it with.

amp and speaker

Also cleaned out and got fixed up the Kerosene lantern, for hurricane use.

kero lantern

That’s about it for now.

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..