Luxman R1500 refurbishment September, 2022
This R-1500 is for sale in the Netherlands, fixed price 500 Euros, cash and Local Pickup as I do NOT ship,I only answer if you provide your phone number also, see the moving mail address on my main page.
Gemakshalve is deze pagina verder in het Engels geschreven.
This page is written using English language only.
This Luxman R1500 was sold to me years ago as "does not receive, after being repaired and recapped".
Apart from it being dirty, there was no sound and indeed no reception.
It was decided, to do a rebuild using separate steps, so everything could be tested in a working unit.
The Luxman R1500 power supply
The power supply card PB758 was to be refurbished first.
It did appear to have a defective Zener diode, supplying the 12 Volts for the tuner circuits.
Apparently, it was repaired before, and while 12 Volts zener was used, apparently it clamped the voltage to some five volts instead of twelve.
Also the protection circuit is on this regulator card, apart from other new parts, the relay used did get a socket.
The card discoloring indicated the power circuit series pass transistor went hot in the past, so a ceramic heat conducting washer was abused and added as a "heatsink".
The rectified voltage for the preamp supply also feeds a big resistor, supplying some 20 Volts additionally to the PB758 board where it is further feeding a resistor going to the said Zener diode.
As this source was to be used for LED scale lighting, the circuit was modified.
The 3300µF and 1500µF smoothing capacitors were both replaced by scavenged newer 6800µF ones, and the diodes by a more sturdy round bridge rectifier.
The big resistor was replaced by a little circuit including two power transistors which were used as attachment of it
This circuit supplies the tuner voltage AND the LED lighting, it consumes some additional 120 milliamps / 5 watts total including LED lighting.
The original lamp wiring from the transformer is not in use anymore, saving 18 watts of lamp power, leaving a 13 Watts power usage benefit.
The two big smoothing capacitors were replaced by 10000 microfarad ones
As the rectifier diodes were 3 Amp ones, the mounting strips carrying them, including "snubber capacitors", were replaced by a single (30 Amps) rectifier carrying a snubber capacitors circuit card.
The power amplifier boards PB760
The power ampl modules were taken out and bench tested using a +/- 35V power supply. One was good the other one had some 5% distortion.
- the distortion
- both had a unknown-brand npn driver TO66 transistor
- one ever had a 47 Ohms resistor replaced where NO technical fault ever could cause a 47 Ohms resistor to burn....
- some other burn flaws
- protection circuits diodes cut out (maybe even by Audioscript, its importer company)
The cards were refurbished, the bias circuitry was replaced by a "vbe multiplier" circuit, employing a BD329 TO126 transistor.
The unknown-brand C783 transistor was replaced by a 2N3585 one.
Notice the VBE multiplier BD329 transistor between the card and the heatsink on the mostright picture, it is mounted using a nylon bolt.
Although the big TO-3 power transistors were still good, I decided to mount MJ15001 and MJ15002 ones, because the high amount of power the receiver can deliver.
RIAA input and microphone input card PB755
This card was not easy to remove, as cables did obstruct. The card was bench tested and the plan was to see if there was any distortion and whether renewal would be beneficial
Right away, also here distortion figures were not alike, and it was decided to just refurbish and test the transistors later.
The refurbished card.
Together with some from other boards, a total of fifteen 2SC1345 transistors were tested.
Four of them appeared seriously deteriorated, as can be concluded from the HFE graph of ten of those, including the four bad ones, below.
Whereas the input signal transistors of the RIAA equalizer are set to a very low collector current, having a very low HFE one in these position would definately compromise the circuit very much, as HFE was almost gone at very low currents.
On the Audiokarma audio forum, this Hitachi 2SC1345 is on some "always replace" list. The bad behavior seems to correlate with the specific transistor package of it.
The PB756 tone control / pre amplifier.
This card was rather dirty, capacitors did leak and attacked leads of other components.
The mike mixer PB759 card.
This one was restuffed, also.
The various switching, PB204 and PB761 cards.
All pushbutton switches were taken apart, cleaned, and remounted. As usual, the spring contacts behave like fleas, and try to escape.
The Tuner related circuits.
The FM tuner front end was untouched, the AM tuner did had its few electrolytic capacitors replaced, and the little AM moise filter pcb carrying a slider switch was left alone.
Luxman importing company "Audioscript", well-known for their service, used to test evey single Luxman device, and they also had an urge to modify as they thought approppriate.
Apparently they decided an "anti-birdie" filter was needed.
The FM IF strip, card PB353was totally recapped. It also has its trimming potentiometers replaced.
Also the anti-birdie filter was recapped, and it has two jumpers on its card, and it was relocated.
It was checked whether there was an audible difference tuning adjacent stations, but I could not hear any difference whether the circuit was in use, or not.
The stereo indicator LED was replaced by a high-brightness type, as it was hardly visible.
Also the anti-birdie filter was recapped, I made it jumper-selectable, and it was relocated.
The refurbished card including the anti-birdy filter, which is technically in series with the stereo decoder chip input:
The schematic of the anti-birdie filter:
At the left, both small electrolytics making one bipolar one, were reversed, and from in between them the jumper is attached in case the signal is routed directly back to the decoder chip, as it was, before.
The filter board PB757 card.
This one was restuffed, also.
The receiver backlighting.
As the tuner meters are severely compromised/discolored due to lamp heating, it was decided to go for LED lighting.
The strips consist of strings of 6 LEDs having one series resistor each string.
Because of an obstructing metal part and the need of a certain width, half a string having extra current regulating parts are on the left part of a strip piece, going behind the tuning meters.
Therefore, the three most left LED's should be tweaked for brightness after the others are set up for the wanted brightness.
As noted in the power supply section, the power is derived from a special circuit, made for this.
An additional trimming potentiometer is used to regulate the lighting of the tuning needle, which has a high-brightness LED now (its lamp was defective...)
The plastic "veneer-alike" was treated using a polymer floor finish.
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