Futile Attempt To Revive A Micro Controller In YAMAHA Tape Deck Model K-340
After experiencing a lot of successful repairs, here is a pathetic story in which this lovely Yamaha Tape Deck could not be saved! As all attempts failed and a service manual could not be provided by the customer, though available on payment basis, I had to reluctantly pack up and return the set. Here is what happened, before which let us look at the inside of this lovely deck, which was brought to me with unscrewed top cover:
The complaint reported by this new referral customer was that this set was lying unused for a long time and it was put to use recently and it was working very well too. But after he moved the Deck to a different place in his home, it did not get on and no functions worked. Usually, when the set is switched on, LEDs in the display panel would glow in full one after the other as a part of self-check done by the Micro Controller. But nothing worked except that the Tape Motor was running when switched on. In many decks that I have seen, the motor running immediately on switch on was a peculiar design and I have no idea why should it be so. Perhaps the whole mechanism depends on the preliminary rotation for any further functional engagements.
When I checked the deck in front of the customer, this was the case. I checked for DC voltages and found these to be ok. The customer, a qualified IT Engineer himself, reported that one transistor regulator and 5V IC regulator were getting hot and I too found the same. As an immediate remedy could not be found without removing the board as the Deck was not having a detachable bottom plate, I sent the customer off saying that I would have a look at it whenever I get free.
Later, I took it up after finishing a couple of successful repairs, for a detailed study of the complaint. I had to remove the front panel and the fixing screws of the board from the rear, and all the connectors so as to take the board out to have a view of the bottom side of the PCB. I observed a couple of dry solders, which I thought might have been the cause and quickly patched it up with fresh solder. Then looked for and found a few more, which also I retouched. The board had a typical varnish coating, which did not prevent or mix with the solder. Then checked the press to on buttons on the control panel and did not find any leak or malfunctioning. The ESR of caps was also well within the range.
I managed to get the datasheet of the Micro Controller IC, which was in Japanese. I got it translated to English online using Google Translator: (Please use cntrl+upward arrow to zoom)
I connected temporary extension wires for the three AC inputs from the transformer and kept the board on top of a component box in order to study the voltage readings.
Let us look at some more pictures before proceeding further:
I checked the voltage to pin 41 and found it to be 5V. The voltages at crystal pins 1 & 42 were also present. I used my DSO and checked the wave forms at both ends and got the following result:
I took the readings of Voltages at each pin of the 42 pin IC and also checked for any more wave forms showing some signs of life. I even changed the crystal and did a dry solder patch up of the IC pins, even though they all looked fine. I removed the load and checked whether the IC was starting. Then removed the mechanical control IC, BA 6229, as any problem in the IC could also cause a shut off. I removed the resistor array (RML S8 103J) and downloaded its datasheet online and checked up using Multimeter for any cross leakage or change of value. This was supposed to be a common one end and each pin was another end of a 10K resistor. It was found to be perfect in reading. So put it back.
But nothing kick started the Micro Con. Then I removed the uController IC itself, as this process would apply some heat to all pins and perhaps it would wake up. Then I put it back. Let us look at a few more pictures:
Since status quo was maintained, I started my desperate way of communicating my predicament to my techie friends and seeking their help. I also sought help from an expert who also was an authorized service point for Yamaha. As per directions and suggestions of these friends, I replaced the filter caps, though these were found to be ok. One techie friend suggested that pin 7 (the reset pin) be disconnected from the board and just touched with a screw driver pin a few times. According to him, this crude method would kick start the IC and sometimes it would wake up. When I tried this way, there was response as the LEDs glowed :
But the IC did not wake up at all and probably the internal RAM would have got corrupted or defective. Then I desperately tried to get a replacement IC through my contacts and the customer also tried his best. While I was waiting for any gleam of hope of luck, I checked almost all the components around the main IC and even replaced a reset transistor and its capacitors. But there was nothing wrong and the main IC remained muted! As these are antique models none of the parts were available! I was at a dead end and was sad that nothing could wake up this set and make it return back to normal working. These are some disappointments we have to put up with and the only solace is the feeling that this could be one among hundreds that we have handled. So, for a change, and breaking away from the usual conclusion of the article, disappointment prevented satisfaction to get entry into the collection bag, leaving dismay to set in! The contentment like a doctor whose patient died, was that I did my best to the best of my knowledge and belief. I kept the removed parts in a cover and taped it on the bottom and informed the customer to pick it up against a nominal recovery of cost of components and efforts put in.
P.S. During the visit of the customer to pick up the set, we discussed about the need of a service manual to make doubly sure that the Main IC is at fault. He agreed and paid advance for purchase of the service manual which was available in https://www.servicemanuals.net/en/ I got the manual promptly and studied it carefully and thoroughly. Did a few more investigations in the set as per chart prepared in Excel with the sad conclusion that the Main IC was faulty. I even tried replacing the 5V regulator with LM7805 as in the set it was 78N05 (300mA). But nothing worked. (The readings given in the chart are without loading the cassette)
If any of the readers know where I can fetch a replacement, please do include in your comments!
This article was prepared for you by Parasuraman Subramanian from India. He is 74 years old and has more than 30 years’ experience in handling antique equipment like Valve Radio, Amps, Reel Tape Recorders and currently studying latest tech-classes conducted by Kerala State Electronics Technicians’ Association. He has done graduation in BBA degree, private diploma in Radio Engineering and retired as MD of a USA company. Presently working as Consultant to Hospital and other institutions.
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Albert van Bemmelen
September 7, 2024 at 7:32 pm
Maybe this LM6405G is still available?
Parasuraman S
September 7, 2024 at 9:13 pm
I saw that already. But it is loaded with a different program as the suffix is 2081 and not 1911. Then, we need to get service manual of that set and there is no way to know in which set it was used!
Anyhow, many thanks for your input!
Rich
September 8, 2024 at 12:13 am
I know your frustration. I repair a lot of control boards that result in a similar experience. Lots of time troubleshooting only to discover it leads to the microcontroller more often than not. As a result, I purchased a low cost logic analyzer. Now the first thing I do is check the microcontroller. Thank you for sharing your experience.
Parasuraman S
September 8, 2024 at 12:33 pm
May I know which low cost logic analyser you are using? Perhaps I can afford to buy it!
Many thanks for sharing my woes and showering cooling solaces!
Yogesh Panchal
September 8, 2024 at 6:13 pm
Sir, It is frustrating but good attempt.
Frank
September 8, 2024 at 9:30 pm
Interesante intento de reparacion.
(Escribo en español, esperando que estos datos puedan servir)
Controlador de 4 bits Yamaha LM6405G-1911 fabricado por Sanyo en la pletina de casete Yamaka K-340. El prefijo LM no tiene relación con el Linear Monolithic de National Semiconductor: es un producto de Sanyo hecho a medida para Yamaha. El sufijo -1911 indica la versión de software incorporada. El LM6402 o LM6405 fueron la opción de Yamaha para la mayoría de sus pletinas de casete después de 1981 o 1982. La pletina Yamaha K-200, casi idéntica, usaba el LM6405G-2081, la K-540 usaba el LM6402G-1919, etc. La venerable Nakamichi ZX-7/ZX-9 usaba el LM6402A-052.
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Interesting attempt at repair.
(I write in Spanish, hoping that this information can be useful)
Yamaha LM6405G-1911 4-bit controller manufactured by Sanyo in the Yamaka K-340 cassette deck. The LM prefix has no relation to National Semiconductor's Linear Monolithic: it is a Sanyo product custom-made for Yamaha. The -1911 suffix indicates the built-in software version. The LM6402 or LM6405 were Yamaha's choice for most of their cassette decks after 1981 or 1982. The nearly identical Yamaha K-200 deck used the LM6405G-2081, the K-540 used the LM6402G-1919, etc. The venerable Nakamichi ZX-7/ZX-9 used the LM6402A-052.
Parasuraman S
September 10, 2024 at 8:09 pm
Many thanks for this wonderful information and comments!
Parasuraman S
September 9, 2024 at 5:55 pm
Thanks, dear Yogesh, for your consoling comments!
Greg Balsley
September 9, 2024 at 9:37 pm
https://www.sierraic.com/LM6405G
Parasuraman S
September 11, 2024 at 7:55 am
Thanks for the lead. I have sent this to the customer!
Waleed Rishmawi
September 10, 2024 at 1:57 am
Sorry I do not have such information about such IC. That is a lot of work spent on that device. Yamaha brands are very complicated and very hard to find.you did what is needed to be done although mission was not accomplished but experience was gained and hard work was spent but we move on and keep doing our best.. thanks for sharing and have a blessed day my dear friend
Parasuraman S
September 10, 2024 at 8:12 pm
Many thanks for your compassionionate comments, dear friend!
Maurice
September 14, 2024 at 10:26 pm
You can find simple logic analysers as low as 5 euro/dollar on aliexpress. And you can use opensource software.
I ordered one but not used yet because off not much time yet.