Newby from London, stuck witha an LC6502C !!

[Dr Jefyll]

BigEd wrote:

I agree with Garth - it looks like the LC6502C is a Sanyo 4-bit microcontroller. [...] I think you're going to need an exact replacement, unless the problem is a flaky clock or reset line.

Hi Mike. I think it's clear we're talking about a microcontroller, coincidentally similar in part number but otherwise unrelated to the sort of 6502 that's our theme on this forum. Nevertheless we're willing to help if we can.

Ed mentioned Clock and Reset, and there are other external things that need to be checked before you conclude that the LC6502C is defective. For example there's the 4 x 4 matrix keyboard with associated diodes which you mentioned. If a keyswitch or a diode were shorted then that would upset operation of the unit even though the LC6502C itself is OK.

That's just one example. Maybe it's pertinent and maybe it isn't, but I can readily imagine others. Unfortunately I'm just guessing, not having seen the schematic. The point is, I think you may be too hasty in concluding the LC6502C is responsible for the malfunction. IOW, the solution might be much easier than you suppose.

Please supply a schematic image -- preferably a scan, but something legible at least. And, do you have access to an oscilloscope?

cheers,

Jeff

[BitWise]

I found a schematic and there is plenty on that board that could go wrong.

If it is indeed the micro-controller that has blown I'd remove it and build a 18F PIC based emulation to plug in to the original DIL holes. Basic functions like button scanning to control the input and volume should be pretty simple. the volume display could be a bit trickier but probably not much.

I'm in the UK it you fancy a crack at it.

[mikefromlondon]

Thanks Micheal for looking into this, yes indeed it is described as a 4 bit Micro, with ROM and RAM, so does that mean it is not the same as the generic 6502 processor used in Atari and other earlier computers such as Vic 20,(I bought that as my first home computer mostly for playing games! I remember the tape recorder that came with it to store programs on audio cassettes, and all those instructions such as Load "Hangman" etc etc! )
Later on I bought the 64K Commodore!

So it is an altogether a different kind of chip from the normal 40 pin 6502. Mrantz no longer support any spares for this amp, what a shame.

I think once I remove my sound chip, this should send the input signal directly to the volume control pots and then to the next pre-amp stage where it passes through 2 op amps to control Bass & Treble control, using a slider potentiometer, except I cannot initiate the Loudness control as it worked through that sound chip, so this will be the only feature I might loose, but then again if I experimented with some caps and resistors across the volume pots to kick in Loudness at low volume, should not be a problem, ideally the amp should have been restored to its original circuit if the parts were available. but thanks for your time looking into this.

[MichaelM]

Mike:

It is not a 6502 processor like the one most on this forum program and develop with. I did find that there were some sites offering the Sanyo LC6502C for sale. However, I'd be cautious in ordering just any old LC6502C from these sites. From the data sheets it is clearly a mask-programmed ROM-based microcontroller. These are generally built with masks that are customized during the final stages of manufacture with a customer-supplied program.

Most vendors of these type of devices provide an ID for the custom part by which it is possible to order another batch. I've never encountered a situation where these custom mask-programmed parts could be ordered by anyone except the original customer. It is surprising, therefore, that what appear to be Asian parts brokers, are offering the part for sale. It may be that your amp vendor simply used a special purpose part developed by Sanyo for the general market, and that is what these brokers are selling.

That doesn't jive with my understanding of these type of parts, so I would recommend caution if you decide to order one or more of these processors from a broker. You may be able to determine from your Amp supplier if it used general purpose LC6502 part. If so, the brokers may be offering that version for sale.

The PIC microcomputer's are very capable processors, and I would probably recommend hooking up with BitWise on a joint project. Now if you really want jump into the deep end, you and BitWise could make use of my PIC16C5x FPGA core.

[mikefromlondon]

Thank you Micheal once again for your worthwhile effort into looking at this for me, I would appreciate if you can give me some pointers to the broker's contact details.

As a last resort I may look at other options, first let us see if I can get hold of it in its original format, ready masked to Mrantz spec.
regards
Mike

[MichaelM]

Here's one address: http://www.hqew.net/buy-components/LC6502.html

I'd be careful. There doesn't seem to be any connection between the LC6502 and the custom program mask-programmed into the part listed for the parts supposedly available.

Here's another which includes a dash number that could be a custom program ID code, or simply a date code: http://www.seekic.com/newstock/TX2_9910 ... 3157_.html

I wouldn't buy anything unless you can determine what program is loaded into the ROM.

Good luck

[mikefromlondon]

BitWise wrote:

I found a schematic and there is plenty on that board that could go wrong.

If it is indeed the micro-controller that has blown I'd remove it and build a 18F PIC based emulation to plug in to the original DIL holes. Basic functions like button scanning to control the input and volume should be pretty simple. the volume display could be a bit trickier but probably not much.

I'm in the UK it you fancy a crack at it.

Sorry BitWise, I must have missed your post earlier, hence a late reply, according to my experience, most chips when they blow,they usually start drawing a lot of current pulling the +5v rail down and chips getting hot to touch, mine doesn't seem to be doing that, so i may have to conduct further tests like resetting ect, once I have figured out which pins are reset etc, so i will let you know how I get on, but for now I will be busy for the next few days on another work related project.

If you could also let me have the electronic version of the schematic, i would appreciate, and I could confirm if it is the same as the paper version i have that came with my unit.

thanks again
kind regards
mike

[BitWise]

mikefromlondon wrote:

If you could also let me have the electronic version of the schematic, i would appreciate, and I could confirm if it is the same as the paper version i have that came with my unit.

I found a 14MB PDF containing a bad scan of the 453/553 service manual. Its not great quality but you can just about make out the circuit. PM me your email address and I'll try to post it to you.

[mikefromlondon]

Micheal, thanks for the links to getting hold of that chip from various companies in HK, but I am sure ordering one costing about 20usd, willbe futile as the program may not be masked for Mrantz or for any other, as these are 4 bit Microcomputers, or controllers. i found a bit more information about them by typing Sanyo LM6502C, there you have the layout of the processor and all its data buses and so on, but still with no pin numbers! and showing various other aspects such as rom and ram areas,clock and so on.

[mikefromlondon]

I think I am going to experiment with this Digital Pot http://docs-europe.electrocomponents.co ... d2a9fc.pdf by interfacing it to Marantz'z volume control chip - TC9177P, as already i have tried using normal mechanical pots and it works fine, since I cannot mount huge mechanical pots on the front of my Amplifier, (as you need twin for a stereo operation) therefore this Microchip could just be the solution I was looking for without requiring a processor to do the job. This way I could use the existing push buttons to do increment and decrement using a slow speed clock to push in pulses to the microchip's u/d control pin, in conjunction with c/s pin. As for the input select, again it is not a problem, I could interface a simple digital latch to control various inputs, as analog gates ate controlled by ttl 5v levels.

Will let you know how I get on, I just hope I can get a Log pot instead of a linear pot. The type I am going to experiment with is MCP 4024, a 50K ohm pot, already I am enjoying the fantastic sound of this amp using the mechanical pot.

This digital pot was designed by Microchip to function specifically without a need for a processor. their quote :
The non-volatile wiper enables the MCP4021/2/3/4 to
operate stand alone (without microcontroller control).