Reliability of electronics

Do you have a question? Post it now! No Registration Necessary

Threaded View
As discussed elsewhere, I commented on the appalling reliability of  
certain items purchased from Jaycar and I expressed my opinion that  
Jaycar should not be relied on for anything sophisticated. Like  
capacitors and transistors.

It got me thinking though. I've been in the service business for quite  
awhile and, when I was Marantz service manager I was issued with a  
confidential list of reliability figures for various Marantz models. The  
list included any reported problem within the 3 year warranty period.  
Here's some of the models I recall:

Model 1070. 0.5% failure rate. Which, I might add, includes the early  
variant which suffered relay problems.

Model 1060. 4% failure rate.

Model 4230. 63% (yes, SIXTY THREE) failure. I put it down to the use of  
very early TO220 pack output devices. These were not reliable back in  
the early 1970s.

All the amplifiers fitted with TO3 output devices demonstrated quite  
respectable reliability, except....

Model 500. 100% failure rate. In fact, each Model 500 usually required  
service several times during it's warranty period. I budgeted 10 hours  
to repair each one. As a consequence, of the 3 amplifiers imported by  
Marantz, only to were sold to the public. It was cheaper to bury the  
last one in landfill. I negotiated a price and I still own the beast. It  
is a highly desirable amplifier. The Absolute Sound reported: "The  
Marantz Model 500 would be issued with our 'best power amplifier ever'  
if only we could manage to get one to operate for more than six weeks  
without blowing up. Designed in 1963, it used, unusual for the time,  
full complementary symmetry outputs. Unfortunately, the Voltage rating  
on the output devices was marginal.

I was a warranty agent for another major brand, when DVD players were  
first released. I was instructed by the Australian agent that their  
first DVD player would certainly fail within the warranty period. They  
were expecting a 100% failure rate. I was told it would be a busy time.  
They were correct.

Re: Reliability of electronics
On 30/05/2022 5:24 pm, Trevor Wilson wrote:
  Designed in 1963,

**Oops. Released to market in 1972, so likely designed in 1971-2.

Re: Reliability of electronics
Trevor Wilson wrote:
=================
Quoted text here. Click to load it

** The model 500 dates from 1973.  
   Each channel used 8 x TO3 transistors with SJ prefixes (  SJ2404 and 2405)  
   So specially selected types made by Motorola.  

   https://www.hifiengine.com/manual_library/marantz/500.shtml

   Rated power was 250W at 8ohms, so 8 devices should be plenty.
   Weight was 83 pounds  -  which is absurd.  




.....   Phil  

Re: Reliability of electronics
On 31/05/2022 9:01 am, Phil Allison wrote:
Quoted text here. Click to load it

**If you've downloaded the service manual, you can see the complexity of  
the beast. SOA adjustments are very comprehensive. The fault with the  
amp lay with the VCEO of the output devices. There was very little  
margin for mains fluctuations. Marantz finally solved the problem by  
specifying 200 Volt, Japanese output devices, rather than the Motorola  
ones originally fitted.

BTW: The Model 500 would typically deliver well over 300 Watts @ 8 Ohms.  
As I recall, around 320 Watts, both channels driven.

Yeah, it's a heavy sucker. Fan cooled too, so heat sink mass is not  
huge. Big power transformer and 4 huge main filter caps.

It was replaced by the Model 510/M, which was far more reliable, more  
compact, lower mass and sounded like shit. Series/parallel output  
devices. Yuk.




Re: Reliability of electronics
Trevor Wilson wrote:  
Quoted text here. Click to load it


**  That assertion makes no sense.  
 Facts:  
 1.  Output transistors do not operate in Vceo mode.  
 2.  They are only exposed to * half* the DC supply at idle or moderate volumes.
  

Quoted text here. Click to load it

** MJ numbered power BJTs all exceed their Vceo ratings on test.
   They way exceeded the ( higher) Vcer rating too - as it almost matches the Vcb rating.  

   SJ numbers have no published ratings.  


.....  Phil  

Re: Reliability of electronics
On 31/05/2022 10:59 am, Phil Allison wrote:
Quoted text here. Click to load it

**Correct. All the US built Marantz models used Motorola devices with an  
SJ prefix. Even some of the early Japanese ones used Motorolas as well.  
Very unusual. I measured a few back in the day. As I recall none of the  
Model 500 output devices exceeded 160 Volts. I may still have a few  
originals lying around. If I locate them, I'll measure the breakdown  
Voltages. Don't forget: It was 1973. High voltage, high power PNP  
devices were very scarce.

Re: Reliability of electronics
 Trevor Wilson wrote:  
 =================  
Quoted text here. Click to load it

** Measured with open base ?   Not how they are used.  

Quoted text here. Click to load it

**  If you do,  put  100ohms  between B and E.
     Makes at least a 10% increase .  
    
Quoted text here. Click to load it

**  SJ types were factory selected from stock, mostly for Vbe matching.
    Crown, SAE and Peavey used them all the time.  

 Total PITA for repairers, who had zero clue what the types really were.  

BTW  

if the Marantz SJs lacked adequate Vce,  examples would have commonly failed bench testing.  
So I don't buy the idea.  



......  Phil  
    






Re: Reliability of electronics
On 31/05/2022 11:52 am, Phil Allison wrote:
Quoted text here. Click to load it

**Will do.

Quoted text here. Click to load it

**Yep.

Quoted text here. Click to load it

**Point taken. When the Japanese devices were installed, the Model 500  
became reasonably reliable. If I recall correctly, most amps failed at  
switch on, rather than under use. I could be wrong.


Re: Reliability of electronics
Trevor Wilson wrote:
=================
Quoted text here. Click to load it


**  I once used to see a lot of Phase Linear 400 mk2 amps.  
    A revised version of the famous PL400 hi-fi model.  
    Complementary MJ output devices and input op-amps on the pcb.  
   These were all used in PA systems - not a good idea.  

   Saw a lot of blown output stages and many that simply went DC taking speakers with them.
   Nothing to do with Vce or even SAO limits.  

The first problem was due to overheating of output devices - since owners had to devise fan cool themselves.
The installed temp cut out was useless, since all TO3s were mounted using thick, pink silicone thermal pads.  
I called the "thermal insulators" as they allowed devices to get 50 C hotter than when mica and grease was used.  

Going DC was due to 5W ww resistors that fed +/- 16V zener regulated rails for the op-amps.  
The resistors were all faulty,  going bright green inside and hence open cct.  

 Did a nice trade in fitting relay speaker protectors in many power amps.  
( wired the RIGHT way so DC arcs were eliminated)  


......  Phil  


Re: Reliability of electronics
On 31/05/2022 1:03 pm, Phil Allison wrote:
Quoted text here. Click to load it

**Good plan. FWIW: The Model 500 never overheated. Thermostat  
controlled, two speed fan cooled. Output devices were all mica/thermal  
paste mounted. Even after repair (using original output devices) the  
amps failed. Only after the output devices were substituted with  
Japanese types did reliability significantly improve. The amp could run  
all day at 40% max power. Easy. Even into 4 Ohm loads.

Re: Reliability of electronics
Trevor Wilson wrote:
=================
Quoted text here. Click to load it

**   Were the SJs in steel or Aluminium paks?  

Early 70s Motorola TO3s had a big problem with thermal expansion of chip headers.  
The silicon and the header had differing tempcos of expansion.  
The end result was the chip developed micro cracks.  

Such devices were speced at a mere 5000 thermal cycles.  
OK for some apps but not class AB audio.  
Sudden, unaccountable failure was the norm.

Aluminium paks got dumped and were never seen again.  


.....  Phil  


Re: Reliability of electronics
On 31/05/2022 2:02 pm, Phil Allison wrote:
Quoted text here. Click to load it

**Like all Motorola TO3 devices of the early 1970s, they were in those  
horrible aluminium packs.

Quoted text here. Click to load it

**Yep. I recall reading the RCA white paper on the issue.

Quoted text here. Click to load it

**Yep. Steel or copper is the way to go for TO3 devices. RCA won the  
argument.


Re: Reliability of electronics
On 31/05/2022 2:02 pm, Phil Allison wrote:
Quoted text here. Click to load it

**BTW: The Marantz Models: 240, 250, 250M, 1120, 1200/B, 140, 2270, 2275  
all used Motorola aluminium cased To3 devices. All demonstrated  
reasonable reliability. None were fan cooled like the Model 500. The  
Model 500 ran much cooler than all those models under normal operation.

Re: Reliability of electronics
On 31/05/2022 2:08 pm, Trevor Wilson wrote:
Quoted text here. Click to load it

Quoted text here. Click to load it

**Oh and with all those models, a visual inspection of the output  
devices would frequently and quickly reveal the problem - A tiny pinhole  
in the case, where, presumably, a piece of white hot silicon ejected  
itself from the header.

Re: Reliability of electronics
Trevor Wilson wrote:
=================  
Quoted text here. Click to load it

**  Ha ha,  no way is that true.  

What really happens is the Al feed wire ( aka fuse) from chip to TO3 emitter pin vaporises.  
This gives a path for a DC arc to jump from the pin to the inside top of the pak.  
A neat hole then gets drilled until the arc self quenches.

Hitachi TO3 lateral mosfets were famous for doing that !!!  


.....  Phil  
  



Re: Reliability of electronics
Trevor Wilson wrote:
---------------------------------
Quoted text here. Click to load it

** The chip in a TO3 can heat in milliseconds - or at least a small part of it can.
   This is why excursions beyond SOA limits are often fatal.  
   High Vces are the killer - aka "second breakdown".  

  Motorola 2N3055s  and MJ802/4502 in Al paks were OK - I used heaps of them.  
  Big chip devices like the MJ15003/4  and MJ15024/5 were not so lucky.  

......  Phil  



Site Timeline