Servicing TEAC A500 Stereo Deck
Before starting reading this article, I request you all to refresh my article on this Deck, published earlier By Jestine Yong on August 29, 2016:
At that time of servicing the deck (July, 2016), I had suggested to the customer for replacement of all electrolytic capacitors as a periodical maintenance, since most of these were in the brim. But he did not agree as he holds an opinion that company’s original capacitors should not be changed unless and until required, as it might affect the audio quality, especially the tone and other effects. Well, since he is an expert in audio, I did not insist and budged to it. This is a point, I would like the expert readers of this article to do comment and clarify.
This was bought by another customer as it was in his use since then. It was brought to me on 17th June, 2018 with the complaint that the relay was chattering. As usual, the first step is to clean the set very well, which I did. Powered it up and left it on and indeed the ‘bird’ started chirping! I disconnected the power, and checked the relay and its surge protection diode and did not find anything wrong. When I powered the relay externally, it stayed on and was not getting hot. Naturally, our attention will be on the power supply section. When I checked the ESR of the capacitors, these were way out and I decided to replace them. When I was desoldering the caps, one leg of a capacitor was found loose and it just came off when I desoldered the other leg! Another had leaked, cracked at bottom and rusted!
After replacing the capacitors in the power supply section, the ‘bird’ stopped chirping! I replaced even the filter capacitor near the relay. Now, as had happened in July, 2016, the control system started its misbehavior, exactly the same way it did earlier! Since I already had the experience of troubleshooting this earlier, I replaced all the electrolytic capacitors on this board and checked the transistors one by one. I did not find anything wrong with it when checked with Analogue Multimeter. In the process, I suspected that the IC had become defective. Removed it, as it was on a socket and checked it separately, keeping it on a breadboard, and applying the power. The required output voltages were not available on two pins, indicating that it indeed was defective. Since I did not want to replace a new one and try it out, without combing the entire control board thoroughly, I put the same IC back, though I had a new one with me (as mentioned in my earlier article). Since the partial defect might only affect certain functions of the IC, it did not matter at that time. But I was yet to lay my hands on the culprit, which surely were one or more transistors on the board. While I was in the process of checking each section, the IC became hot and I switched off the set immediately and noticed that it had developed a crack on top.
So, I had no alternative but to replace it. But I did not want to do so without checking the board further. That’s when I decided to declare another war with this set. I removed every transistor on the board (41 numbers in total), writing down the reference numbers on the board and that on the transistor. I kept my Peak Atlas permanently connected to three pins on a small breadboard to avoid using its clips each time for checking the 41 transistors. It served as a test jig. I marked the transistor numbers on the circuit diagram too. Then noted down the condition of the transistor alongside, after putting a tick mark for having checked it.
The transistors were misbehaving in such a way that it will show defect when inserted in the breadboard, but will show ok when rechecked. In fact, it was some sort of comic like Tom and Jerry! But I caught a couple of real culprits too! I had segregated the transistors based on the numbers, i.e., C945 (NPN), A933 (PNP), D313 (NPN), C1741 (NPN) and C1645 (NPN). So, when checking, I also segregated it based on the HFE, like a quality inward checking in ‘Goods inward department’, and kept out the defectives! I rechecked the defective transistors by connecting the test leads directly.
So, the decision was to replace all the 41 transistors on the board, because of intermittent behaviors of some. I bought replacement transistors and subjected it to quality checking like before, segregating it on HFE basis. I wanted to use transistors which have closer HFE in each section. This is another way of ensuring proper functioning. Even in the new transistors, I found four of them defective!
After quality checking, I replaced all the transistors one by one, putting a round mark on the list which I had prepared earlier and simultaneously putting a tick on the circuit diagram whenever a section was completed. I kept the circuit diagram beside to populate the transistors with closer HFE in each section.
Here is the board put back in its place, after completion of the work, replacement of the IC and its socket (reason for failure of the earlier IC, due to loose contact):
Powered the set and found it to be working very well. Ran it for several hours.
Ran the tape and checked all the functions including recording. It was working superfine now!
Reassembled the set and transferred it to delivery room! (Sit out of my house!)
I forgot to mention that I had replaced all the electrolytic capacitors in the deck this time. Here is the picture of the components replaced, as well as those found defective in inward quality checking.
Thus, my ‘satisfaction list’ bulged further and extended itself farther! Looks like my satisfaction bag is like Lord Ganesha, who is believed to be capable of swallowing everything in this world, but still remain hungry! (LOL)
By the way, this is my HUNDREDTH article being published by Jestine Yong, and I thank him as well as all of you who have encouraged me and kept me driving ahead! A BIG THANK YOU to one and all! I am so excited over this achievement that I feel like dancing! (LOL)
This article was prepared for you by Parasuraman Subramanian from India. He is 69 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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You may check on his previous repair article below:
https://jestineyong.com/burst-fbt-found-in-21-crt-tv-with-china-kit/
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Robert Calk Jr.
November 20, 2018 at 2:24 pm
Thanks Parasuraman. Congratulations on article 100! I'm not sure that that cassette deck is worth the time and money that you have spent on it. But thanks for the article.
I always hook my analyzer probes directly to the transistors no matter how many that I check. That way you have a more secure connection with less added capacitance and resistance. You can buy new grippers.
As for your question about him refusing before to have the e-caps replaced, I would have refused the job if he didn't agree to at least replacing the e-caps in the power supply section. But I'm just a hobbyist.
Parasuraman S
November 20, 2018 at 7:02 pm
Thanks! Yes, you have a point there about directly connecting the grips. But I used this method for easiness and to avoid the need for engaging all the three grips each time because of the bulk quantity of components to be checked. As far as refusal by the customer, we cannot do anything when he is a close friend! Otherwise I would have refused!
Robert Calk Jr.
November 21, 2018 at 3:07 am
Yes but when it stops working soon after you repaired it, it is you that looks bad, not your friend.
Parasuraman S
November 21, 2018 at 1:20 pm
Yes, true. But not with the same customer. Both the seller and buyer are my friends. In certain cases, when customers who are close to me are adamant, I have to budge giving weight to the relationship than perfection. In this case, when the A was selling to B, A wanted to keep the repair charges to the minimum so as not to overshoot the marketable price of the device. B took a chance, but burnt his fingers! But he does not mind, as he wants to use it and might not resell without taking its life! A is always like that, and he seldom allows me to replace capacitors as he holds a strong opinion that the audio quality will get affected! Well, we have to deal with all kinds of customers in our field!
Robert Calk Jr.
November 22, 2018 at 1:24 am
If he is concerned about audio quality I wonder why he hasn't moved into CD players? One of the best things I did was to trash my cassette player and buy a CD player. If he has cassettes that aren't available on CD, he can get a device and program that will allow him to transfer his cassettes to CD's. I used "Audacity" to transfer my dad's home recordings he had on cassette to CD's. It worked great!
Albert van Bemmelen
November 20, 2018 at 3:56 pm
This repair again proves the professional and meticulous way in wich you patiently remove every bad component and disorder in failing consumer electronics! Congratulations with achieving this memorable repair count Mr.Parasuraman!
James
November 20, 2018 at 4:50 pm
An amazing amount of work and dedication there, and very inspiring, thanks for sharing your work it's beautiful 😉
Andre Gopee
November 20, 2018 at 6:13 pm
I agree with Robert, I would not take the job. Once E-Caps begin to go bad, it is wise to replace all with good e-caps. When I am testing transistors and I get different reading I usually use different testers to see if I am getting the same results. I hope the customers appreciate the job you did and compensates well. Great Job.
Suranga Electronics
November 20, 2018 at 7:00 pm
Hi. Parasuraman.
Wow.. Good Repair Job. Well done
Audio Expert !
beh
November 20, 2018 at 7:48 pm
Thanks for your all efforts to rebuild this old machine, but you did not told any thing about bad mechanical parts of cassette compartment itself by my experience rarely you may find the parts in the market unless otherwise in salvaged parts .I am sure you had this problem as well as other problems specially in capstan ,and roller or motor and belts and door springs and eject button and /or other mechanical parts ......
cheers
behzad
Parasuraman S
November 20, 2018 at 11:50 pm
The cassette mechanism is very sturdy and nothing was bad in it.
Carlo Alberto Birocco
November 21, 2018 at 5:16 am
Mr. Parasuraman,
it seems a complete rebuild of the deck, not only a restoration!
Only your mighty perseverance could lead to fix this issue.
Good job! Bye
Carlo Alberto
Yogesh Panchal
November 29, 2018 at 4:19 pm
EXCELLENT!
Raju Varghese
December 2, 2018 at 4:31 pm
Dear Parasuraman,
Good Morning!!! hope you are doing well...
Excellent job and great attempt.