400A Repair
Hi Barchetta,
I thought twice about whether or not to repost this,
as I'm sure many folks saw it the first time.
However, I wanted to perhaps offer you some timely encouragement in the form of a completed example
that might bolster your resolve in case of difficulty.
(My apologies to those who have seen this before)
To rework the Front Plate and the Rack Handles,
I started out with heavy grit (100) sandpaper
on a power sander to remove several bad dings in the
metal, then gradually worked my way up to 600 grit
wet paper (water sanding by hand). I finished
up with #0000 steel wool and detergent to remove
oils and residue and polish the surface to bring out
the shine.
To protect the finish, I then shot the plate and handles
with a thin coat of clear enamel. The whole project was a LOT
of hard work, but I have discovered over the course
of many years of restorations that the pieces I work
hardest on are the ones I value the most in the end!
Best regards,
Terry Keith
Hi Barchetta,
I thought twice about whether or not to repost this,
as I'm sure many folks saw it the first time.
However, I wanted to perhaps offer you some timely encouragement in the form of a completed example
that might bolster your resolve in case of difficulty.
(My apologies to those who have seen this before)
To rework the Front Plate and the Rack Handles,
I started out with heavy grit (100) sandpaper
on a power sander to remove several bad dings in the
metal, then gradually worked my way up to 600 grit
wet paper (water sanding by hand). I finished
up with #0000 steel wool and detergent to remove
oils and residue and polish the surface to bring out
the shine.
To protect the finish, I then shot the plate and handles
with a thin coat of clear enamel. The whole project was a LOT
of hard work, but I have discovered over the course
of many years of restorations that the pieces I work
hardest on are the ones I value the most in the end!
Best regards,
Terry Keith
Thanks Terry.. I have a lot of automotove finish experience.. So this part will be "easy" for me.. I also have some of the proper equipment to get the job done quickly.. Not sure if I will go your route though.. I'm a but of a stickler for the original look.. I may bring mine in and have it anodized (or do it myself; not too hard really) and try and source a plastic logo badge like my other 400a has. But not I am thinking WAY too far ahead since I have 12 transistors laying in front of me!
Steve: From Jon? Original Motorolas. Used $8. and new $15. I just used a continuity test. One or 2 were shorted all directions BE and C (C is the mount right?). I dont think power is an issue for a continuity test?? I mean if they are open in all directions is that questionable? For example B to E both polarity directions?
I'll try and follow your links to one of the testers in case you think I need to get one... let me know and I will see about ordering one... Ya know; there is a shop I might be able to stop into and ask them to test them.. hmmmm
Edit: any of these work?
http://cgi.ebay.com/B-K-Model-162-T...ameZWDVWQQrdZ1QQcmdZViewItem#ebayphotohosting
http://cgi.ebay.com/Digital-transis...oryZ1504QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
j
Steve: From Jon? Original Motorolas. Used $8. and new $15. I just used a continuity test. One or 2 were shorted all directions BE and C (C is the mount right?). I dont think power is an issue for a continuity test?? I mean if they are open in all directions is that questionable? For example B to E both polarity directions?
I'll try and follow your links to one of the testers in case you think I need to get one... let me know and I will see about ordering one... Ya know; there is a shop I might be able to stop into and ask them to test them.. hmmmm
Edit: any of these work?
http://cgi.ebay.com/B-K-Model-162-T...ameZWDVWQQrdZ1QQcmdZViewItem#ebayphotohosting
http://cgi.ebay.com/Digital-transis...oryZ1504QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
j
An anodizing shop will dip the parts to remove the existing anodizing. It will remove a thou or two but the part will be clean.
Then, you can either have the parts brushed or polished and re-dipped clear or black.
I'd do all of the heatsinks at the same time while it's apart.
You can even have any imperfections in the metal tigged up so there are no gouges or deep scratches (if there are any).
It will look like new then.
It shouldn't cost too much.
I like the digital tester in your second link. The sockets are very convenient. I want one!!!
I just wish you had one good known transistor to test with your meter so we know that your testing procedure and meter are correct. Then, I'd trust all of your other readings...
Then, you can either have the parts brushed or polished and re-dipped clear or black.
I'd do all of the heatsinks at the same time while it's apart.
You can even have any imperfections in the metal tigged up so there are no gouges or deep scratches (if there are any).
It will look like new then.
It shouldn't cost too much.
I like the digital tester in your second link. The sockets are very convenient. I want one!!!
I just wish you had one good known transistor to test with your meter so we know that your testing procedure and meter are correct. Then, I'd trust all of your other readings...
Hi barchetta,
Okay, I'll try to help here.
Buy all new outputs from the same batch. Buy a couple extra. Build a basic circuit to measure beta and try to get the positive and negative banks of transistors to match in beta (or hFE = gain). Use the others for the cascode positions.
Transistors do last a long time but do have a failure mechanism. There is a failure rate and as Apogee stated :
-Chris
Okay, I'll try to help here.
Buy all new outputs from the same batch. Buy a couple extra. Build a basic circuit to measure beta and try to get the positive and negative banks of transistors to match in beta (or hFE = gain). Use the others for the cascode positions.
Transistors do last a long time but do have a failure mechanism. There is a failure rate and as Apogee stated :
When an output shorts, some other parts are stressed even though they did not fail at that time. It makes sense to replace the lot. You will own the amp for a long time I bet. Decide if you want to do the other side at the same time. Do not mix transistor types.
-Chris
anatech said:
Aparently you have not tried to source these.. there is no "batch". Not in Motorola brand anyway.. and Steve is pushing me to be brand loyal here.. nope; a batch is not available unless you know something I do not. But I do hear you about replacing them all and I had planned on it since they are all dead anyway as I mentioned.
Any thanks for the anodizing comments.. I think if the aluminum is treated with a chemical though it can just have additional anodizing added.. pretty sure.. that would save a ton of work if thats the case!!
Zen Mod said:
hehe
even if Chris is just a human.......(or isn't ? repair techs are rarely humans) - he's certainly in repair business from time when your and mine GrandPa were in shorts............
I can't really understand this.. if your point is that he already knew they were hard to source in batches thats fine.. but it doesn't help me any if I do not know where they are. If someone has a source please post it.. otherwise lets just stay on topic.
Apogee said:
I will pull a good one tonight and tell you what my test looks like.. that should make you feel much better.. but I am just going by what I have been told to test.. and thats to do a simply test across the e and B to see if it looks like a simple diode.. and most look like air to me
like I said one or two were DEAD shorts.. ALL of them (B,E,C). I think I will bring them into a repair shop.. buy some interconnects and ask them to test them real quick..
barchetta said:
it is your job and task to repair that amp,even with help ;
it's also your job to carefully read entire thread ,just to try to squeeze every ounce of useful information ......
Chriss didn't tell you in this post which transistors you need to find ; I think that he already (or someone else ) wrote that you can use some more modern ,or less ancient, type of outputs.
and-btw , parts are always made in batches ............ are they coded as batches or they aren't ,that's another issue .
but -mostly they are coded........even in hysteric Motorola way ......in that case we need Code Machine for their codes........
btw- you don't need anyone else to check transistors for you:
( regarding stayin' on topic- just think that-when you repair amp or Porshe,you also work on self-repairing.......
Attachments
Zen Mod said:
it is your job and task to repair that amp,even with help ;
it's also your job to carefully read entire thread ,just to try to squeeze every ounce of useful information ......
Chriss didn't tell you in this post which transistors you need to find ; I think that he already (or someone else ) wrote that you can use some more modern ,or less ancient, type of outputs.
and-btw , parts are always made in batches ............ are they coded as batches or they aren't ,that's another issue .
but -mostly they are coded........even in hysteric Motorola way ......in that case we need Code Machine for their codes........
btw- you don't need anyone else to check transistors for you:
( regarding stayin' on topic- just think that-when you repair amp or Porshe,you also work on self-repairing.......
PLEASE I am asking this NICELY.. leave me alone.. I do not want your advice, your comments, your anything.. just go bother someone else. Thanks!
barchetta said:I will pull a good one tonight and tell you what my test looks like.. that should make you feel much better.. but I am just going by what I have been told to test.. and thats to do a simply test across the e and B to see if it looks like a simple diode.. and most look like air to me
On good devices, the BE and CE look like diodes. On bad devices
the CE is usually a short.
Don't obsess over batches and stressed transistors - let's
just get this thing running, and if you have problems in the
future you will be able to tackle them with your newfound
skills and confidence.
I think I've got some of the 5876 and 5878's in a bag, and
I'll send you enough to replace the known bad devices.
Nelson Pass said:
On good devices, the BE and CE look like diodes. On bad devices
the CE is usually a short.
Don't obsess over batches and stressed transistors - let's
just get this thing running, and if you have problems in the
future you will be able to tackle them with your newfound
skills and confidence.
I think I've got some of the 5876 and 5878's in a bag, and
I'll send you enough to replace the known bad devices.
Mr. Pass.. no no no.. I can get these.. THANKS.. no no.. you have done too much already! I'll just order these from Jon.. and your post confirms.. all of them were bad on the one side.. I'll call him tonight..
thanks for the extrememly generous offer.
I'll see if he can't outfit me with the caps and resistors too at the same time.. he could save me a bunch of hassle.
barchetta said:
Actually.. if I do re-anodize this unit I might ask if I could send the front plate to you for a signature.. that would be an awesome last touch to this unit!! Since you are feeling so generous and all I thought I would ask!
Left a VM for Jon.. I will get these ordered and get back to you guys when I get them and all the other parts installed.. I'll need some help with bias I think.. I noticed my existing unit might be running cool.. I can hold the heat sinks as long as I want after its warm and I noticed the right side heats up slower than the left.. probably out of adjustment?
I just got a private message from the moderator here and have decided that its best if I leave this forum permanently.
Steve, Mr. Pass, I appreciate all you help.. you have both been very kind.. its unfortunate it has come to this.
Trust me I will get this amp up and running..
Moderator(s): Please feel free to delete my account if you wish.
Thanks
Joe
Steve, Mr. Pass, I appreciate all you help.. you have both been very kind.. its unfortunate it has come to this.
Trust me I will get this amp up and running..
Moderator(s): Please feel free to delete my account if you wish.
Thanks
Joe
What the...!?
I know things got off to a rocky start, but I was under the impression everything was going smoothly. Will someone please explain to me in plain English what's going on here?
Joe,
Once upon a time I was "the" moderator here. It was the only time that there has been only one moderator at this site. I didn't really have any authority or power; it was more of a figurehead position. There's one policy that I was adamant about, and I defended it to all comers...everything and I mean absolutely everything I ever said was said here on the site. It was--and remains to this day--public record. Always. None of this sneaky-sneaky stuff. This is a perfect example of why I felt it was necessary to do things that way. I, for one, see no reason for you to leave the site. In a case like this, I'd like to know who said it, and why.
Back when I was moderator, this crap didn't happen.
Grey
I know things got off to a rocky start, but I was under the impression everything was going smoothly. Will someone please explain to me in plain English what's going on here?
Joe,
Once upon a time I was "the" moderator here. It was the only time that there has been only one moderator at this site. I didn't really have any authority or power; it was more of a figurehead position. There's one policy that I was adamant about, and I defended it to all comers...everything and I mean absolutely everything I ever said was said here on the site. It was--and remains to this day--public record. Always. None of this sneaky-sneaky stuff. This is a perfect example of why I felt it was necessary to do things that way. I, for one, see no reason for you to leave the site. In a case like this, I'd like to know who said it, and why.
Back when I was moderator, this crap didn't happen.
Grey
GRollins said:
Well; I was told I was too thinned skinned by the "chief moderator". Oh and how lucky I was to be getting this information (no kidding? really?!.. like I havent expressed my deep appreciation???) I was not asked to leave.. but hot damn if I am going to be told its "My job" to do this and "my job" to do that.. by someone here and not respond back... the whole tone of the post here was just so off the wall compared to how it was going..
So; I just got off the phone with Jon @ Vintage.. and I am excited to find out I was testing those damn things wrong. (you just cant use any old ohm tester). and he explained how to do it with my diode tester on my multimeter.. and he explained ALL sorts of things to me.. how to set bias .. what breaks; what you should replace.. blah blah.. all great stuff. All this in about 5 minutes (I didnt want to keep him.. let him go as quick as I could).. What a guy! I wish I could afford him! He probably does a fantastic job!
yippeee.. off to order parts!
Oh and he explained how to tweak my GOOD 400a.. its running way too cool.. and he said I can really smooth out the top end.. (but I am not touching that one until this one is fixed)..
P.S. things were great here until a certain someone HAD to chime in.. the rest of you guys have been great.. I guess if I were moderator the personal email would have gone to the "other guy".. but of course thats how it looks from my side..
Okay; once again Steve has convinced me to swallow my pride and come back. I can see where I may have come off being flippant and I apologize for my poor wording. He explained that there are many who are too timid to ask that are benefiting from this thread. In this spirit I'd like to try and "give back" in the only way I know how...
In regard to testing transistors for those that have very limited knowledge and very limited equipment available.. (sound like anyone??).. here is some data:
When testing the 2n5876/8 transistors it was suggested to run resistance (Ohms) tests across the Emitter Base and Collector.. and that there should be a little diode network from the collector to base and base to emitter. While this is of course true a simple Ohm meter does not always work (I suppose it does sometimes depending on the meter used and the actual component.) To illustrate:
Here is the base to emitter with an Ohm meter: note it read infinite (open)..
Now; MY multimeter has a diode tester on it thank goodness.. when I switch to it sometimes I get a little shock from the test leads.. so I assume the output is higher from the poor little 9volt transistor battery inside.. now here is what that test looks like in both directions:
Note: same polarity but test indicates a diode will allow current in this direction..
Now the other way..
This one shows "open" in not so knowledgeable terminology..
Edit: I decided to shoot and post one more in the interest of clarity.. this is what the meter looks like in diode test mode with an open circuit..
Same with the collector test (which is the mount itself of course..).. from the base..
So this one is good.. a bad one shows (on my tester) current in both directions.. I did not see one open in both directions with the diode tester.. not to say that could not happen cuz I am sure it could given enough current..
I hope this helps someone and if I made an error I am absolutely certain beyond any doubt that someone will correct me! And sorry to bore the hell out of others.. but I think this type of info is in the spirit of this forum..
Joe
In regard to testing transistors for those that have very limited knowledge and very limited equipment available.. (sound like anyone??).. here is some data:
When testing the 2n5876/8 transistors it was suggested to run resistance (Ohms) tests across the Emitter Base and Collector.. and that there should be a little diode network from the collector to base and base to emitter. While this is of course true a simple Ohm meter does not always work (I suppose it does sometimes depending on the meter used and the actual component.) To illustrate:
Here is the base to emitter with an Ohm meter: note it read infinite (open)..
An externally hosted image should be here but it was not working when we last tested it.
Now; MY multimeter has a diode tester on it thank goodness.. when I switch to it sometimes I get a little shock from the test leads.. so I assume the output is higher from the poor little 9volt transistor battery inside.. now here is what that test looks like in both directions:
An externally hosted image should be here but it was not working when we last tested it.
Note: same polarity but test indicates a diode will allow current in this direction..
Now the other way..
An externally hosted image should be here but it was not working when we last tested it.
This one shows "open" in not so knowledgeable terminology..
An externally hosted image should be here but it was not working when we last tested it.
Edit: I decided to shoot and post one more in the interest of clarity.. this is what the meter looks like in diode test mode with an open circuit..
Same with the collector test (which is the mount itself of course..).. from the base..
So this one is good.. a bad one shows (on my tester) current in both directions.. I did not see one open in both directions with the diode tester.. not to say that could not happen cuz I am sure it could given enough current..
I hope this helps someone and if I made an error I am absolutely certain beyond any doubt that someone will correct me!
And sorry to bore the hell out of others.. but I think this type of info is in the spirit of this forum.. Joe
I'm getting feedback on this both on and offline. I appreciate your clarification as to whether you were being asked to leave the site or not, as that was bothering me considerably. On the other hand, I can understand how an e-mail that sounded the way this one apparently did could be upsetting to you.
Who's at fault here?
Everyone.
Okay, not everyone...not literally...but it looks to me as though there's enough blame to spread around. My guess is that there are certain personality types that you don't get along with. I, myself, may be a marginal case, so I've remained on the sidelines for the most part. In any event, it seems that you and Apogee have been getting along swimmingly, and that the poor amp has been getting proper care.
In the process, you might begin to feel that you can trust at least some of the members here. If that journey begins with Apogee, then take the first steps with my blessing.
I'll know this thread was a success if I catch you on ebay bidding on another dead Threshold.
Grey
Who's at fault here?
Everyone.
Okay, not everyone...not literally...but it looks to me as though there's enough blame to spread around. My guess is that there are certain personality types that you don't get along with. I, myself, may be a marginal case, so I've remained on the sidelines for the most part. In any event, it seems that you and Apogee have been getting along swimmingly, and that the poor amp has been getting proper care.
In the process, you might begin to feel that you can trust at least some of the members here. If that journey begins with Apogee, then take the first steps with my blessing.
I'll know this thread was a success if I catch you on ebay bidding on another dead Threshold.
Grey