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Fusible resistor in A-1

Nashou66

Nashou66

AK Subscriber
Subscriber
Reposting this as it got lost in the server issue AK had today.


What is an acceptable resistor the FR102 in the A-1. It is a Micron 68 ohm but it has a 60mA rating, that is what threw me. Most I see are wattage, but this is current rated. I did a search on Mouser etc but came up empty on any Current resistor fuses.

Nashou
 
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I got this response from a member i forgot who it was.

"You will not find this kind of fuses resistors on MOUSER . You have to choose modern type if you don't have original type .

I am sure that you know U=R x I and P = U(2)/ R so you have your answer

0,244 W !"

I then asked where these numbers came from to figure out the .244 watt resistor. I know we have the 68 ohm and the 60mA fuse.


Then I was told to just use a 1/4 watt fusible resistor.

But I know that the way those fusible resistors work is they get real hot and burn, but I don't think fast enough for that circuit. Id rather get the
safety of the proper current limit of 60mA's WITH OUT the heat.

So talking with a very knowledgable tech he suggested to use a regular or even the fusible 68 Ohm resistor with a 62mA pico fuse in series. Which is basically
what the original Micron HW 29468 is in a single case.


Id rather be safe than blow more parts while diagnosing the amp.

Thanks guys !

Athanasios
 
Good luck trying to solder pico fuses without damaging the fusible element.
 
hello Nashou66

I said "you never find such resistor on Mouser " because you will not find the same model and brand not that you will not find 68 ohm !!
Of course you will !!
but what is the trouble with your " resistors " ? Are they good ? bad ?
Follow what Avionic said he knows about what he is talking about
I have hundred pieces of this kind of resistors and sending you one from France would be silly in regard of the cost of 10 bought at MOUSER !
 
Thanks Guy's

Resistors blew while scoping the drive transistors for the main power transistors. Blew R102 and the fusible.

My fault I tried to keep the contact made while I reached to change a scope setting. Ugh, well it blew the main power transistors too.

I ordered those from UTSOURCE got all 4. I have ordered parts from there for some hard to find Flyback amps for
my Electrohome Marquee 9500LC CRT Front Projectors vertical deflection board.

Nashou
 
Well finally after tracking down the distortion on the left channel It was R113, the .47 ohm 5 watt resistor. I replaced
a bunch of parts that were bad. One of the drive transistors, the 330 ohm resters, the fusible, then I accidentally
shorted the main output transistors . I was still getting distortion after I got the amp running. So I figured that since I had sound I'd better adjust the DC offsets and other
parameters of the amp. thats when I got to the idle current and it had no reading and no adjustability . Just read .001 mV's. So i looked at the points that the
Left channel Cap board read from TP2 and TP4, i then realized that the board drawings have it backwards. Those test points are for the Right channel CE and RO respectfully.
SO I looked at where the signal goes from CE and LO and they go through R113. So I tested it in circuit and got 2.3kohm's, I pulled it and it read OL , shorted.

I had a 1 ohm 5 watt i pulled form a crossover re build and used that for now
and all is well.

here is what a 1 kHz tone on the -E signal looks like , good right channel top and the one with R113 blown bottom.

25054969674_124680360e_c.jpg



I ordered the Ohmite Audio Gold Resistors from partsconnexion for all 4 in the amp.
Not sure if they'll improve the sound much for the extra money but this is a nice amp.

http://www.partsconnexion.com/prod_pdf/ohmite.pdf


Now that this is almost finished I can move onto the Yamaha A-3 repair.

25116469579_1abbfb5614_c.jpg
25414095335_4be30c0bfa_c.jpg



This will be fun too! No , service manual , Schematics or User manual . :D

Athanasios
 
Last night I was working on fixing a hum and channel drop out on this A-1. Not sure if it was the Philips AF877 turntable connectors or the
A-1's phono inputs. So I took the panel off and cleaned the phono input board and connectors. Put her back together and tried again. A little better but then realized it might be the right plug from the TT. So i re wired the connector and the right was fine but now the left was iffy. But it was late and went to bed. Went to work came home and the Ohmites arrived in the mail. Relaxed a bit and heard some strange noises in the basment. Hmm went to investigate and the A-1 was still on ! I left it on all night, it was warm and making strange noises from the right speaker. OH NO I thought ! After all this work !!! I let it cool for a bit then hooked up a source to check it out. Damn it right channel is now distorted.

Well i got the ohmites so i decided I'll install those and then diagnose the issue. I pulled the old microns and when I did i decided to test them all for Shits and giggles. sure enough another one was out on the right channel this time. it was the same issue. installed the new ohmits and all is well again. Tomorrow I will re solder the left phono cable on the AF-877 and hope that was the phono issue.

Here are the Ohmite Audio Gold resistors installed. I used the cloth insulators as well as heat shrink on the exposed leads.

25950847066_3a71952212_c.jpg


Almost done here .........I hope . ;)

Athanasios
 
Hello
The original resistors you have replaced are not fuse resistors . They are cement resistors .The white resistors we can see on your picture are emiter resistance and need to be able to protect your amp by the fact they should no burn . I don't think that the model you use is correct for this purpose .
Good quality cement resistors can be bought on MOUSER . If you choose these OHMITE resistor for a question of "quality of sound" it is not necessary at all here . The sound of your A1 will not be improved by any manner at all .Did you think to choose the "non inductive" version ?
Replacing your adjusting potentiometers will be much better choice and bring you reliability of adjustment .
 
Thanks Patrice, Yes i know these are not the ones I started the thread about. But I found one to be open on the originals, and then another also went open. So I ordered these Ohmites for those that were open and I figured Id replace all four in that circuit. I had some other parts i needed as well from the same source so I added these to the order to save on a separate shipping cost, that made up for the slight cost increase of the Audio Golds.

Also I thought these resistors tie together the output transitors and act as a balancing resistor between the two? Still learning here..... but anyhow the old ones may have been getting tired. I do plan on replacing all the trim pots as well. I used a Yeago fusible for the 68 ohm fusible.

Also I think the relay needs changing. I am getting a static sound intermittently from the right speaker and the relay protection goes on . Then after some time the speakers come on again with less static but then it goes on again , turning the speakers off. This may not happen for
a half hour to full hour then happen every few minutes. And this happens with no source connected and with any input selected. What could this be?

Athanasios
 
Many relays can be snapped apart and the contacts cleaned with some very fine abrasive paper. 800 on up is good, but I like even finer polishing films. If the contacts aren't pitted at all, don't use abrasive paper, just pull some regular paper through them with a bit of DeOxit on it. Make sure the relay voltage matches the coil and if not, troubleshoot that part of the power supply.
 
ConradH said:
Many relays can be snapped apart and the contacts cleaned with some very fine abrasive paper. 800 on up is good, but I like even finer polishing films. If the contacts aren't pitted at all, don't use abrasive paper, just pull some regular paper through them with a bit of DeOxit on it. Make sure the relay voltage matches the coil and if not, troubleshoot that part of the power supply.
Click to expand...

Relay 101 can be opened right on the board . I sprayed De Oxit in that a while ago. But can RY102 also be opened? It is the clear one.

And How do I check the relay voltage so they Match the coil?

PS: I ordered new relays for RY102 and new trim pots .

Thanks

Nashou
 
Don't know them specifically but if it's got a plastic case it probably comes apart. If it's potted, then no. Almost all relays have the voltage printed on the case or encoded in the part number. What often happens is the part of the power supply that feeds the relay coil gets a bad cap or other part. The relay then gets enough voltage to work, but the holding force is weak and the contact goes a bit intermittent or the sound gets distorted.
 
ConradH said:
Don't know them specifically but if it's got a plastic case it probably comes apart. If it's potted, then no. Almost all relays have the voltage printed on the case or encoded in the part number. What often happens is the part of the power supply that feeds the relay coil gets a bad cap or other part. The relay then gets enough voltage to work, but the holding force is weak and the contact goes a bit intermittent or the sound gets distorted.
Click to expand...


Understood ! Thanks !

I did notice on the PS board that the two heat sinked transistors/regulators were loose from the heat sinks. Might be over heating lowering voltage output. I have to look at schematic to be sure if they are involved.



Nashou
 
Double check if you have any DC offset on the channel with protection relay working after a certain lap of time . Make this measurment between emitor of each output transistor and ground . You should have zéro volt (not more than 10mV)
Changing it by a new one will not cancel the problem ..In a unit old like this one , it is always a good idea to use brand new relays
 
clinic-audio said:
Double check if you have any DC offset on the channel with protection relay working after a certain lap of time . Make this measurment between emitor of each output transistor and ground . You should have zéro volt (not more than 10mV)
Changing it by a new one will not cancel the problem ..In a unit old like this one , it is always a good idea to use brand new relays
Click to expand...

After I changed the .47 Ohm 5 W resistors I re checked all the voltages and Offsets( except the VR board >200mv setting) the pots are definitely in need of changing as they wont stay
set and drift up and down but finally settle, somewhat ;) . But I think they might rise once I move it from my Work bench to my testing location where they drive a pair of IMF TLS80's I am working on as well.
The Drive board test points on right settled at 6mv the left is the one that fluctuated If my memory is working ok. At work tonight so no more checking till tomorrow or later tonight.

I use a dummy load for testing, a pair of 8 ohm 100W resistors on a heat sink.

nashou
 
Oh And Patrice this happens when no source is connected and I think with the volume down , this is why it leads me to a relay issue.
 
Conrad was right !!!

I removed the voltage regulators on the PS board and the heat thermal grease was tired out and the heat sink was very loose on it.
I noticed before the heat sinks were not even very hot but i felt a lot of heat coming from that area.

Here you can see the darkening of the PCB. I did as another member did and raised the heat sink off the board with a small washer, reapplied thermal paste
and installed the parts and gave her a listen. Nice and clean for a half hour. Also the heat sinks got hot this time around. Working as they should pulling heat away from the IC's so
they work at optimal performance.

25895840722_2ea4fbc468_c.jpg
25895840662_226860b4cd_c.jpg
 
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