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 Post subject: Masterworks M2894 restoration
PostPosted: Mar Thu 22, 2012 5:17 am 
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Joined: Mar Thu 22, 2012 4:51 am
Posts: 9
I am in the process of setting up my electronics hobby shop and new to the site. I recently acquired a vintage Masterworks M2894 shortwave radio that is not working. As I wanted to restore this radio while learning the "how to", I purchased the schematics and repair manual from the Sams Photofacts but his this does not include the disassembly of the radio.

I studied the case carefully but the location of the screws to fully remove the chassis from the case is not at all obvious. All I was able to do was remove 4 of the screws that was outside the case but this does not allow me to remove the entire chassis.

I would greatly appreciate if anyone has information or suggestions re how to go about this. Obviously I have searched the net quite a bit but can not find much info on this.

By the way I find this site very useful and plan to be active as I both learn and contribute in the future. Eagerly await any suggestion to my problem with restoring this nice radio. Thanks to all in advance
Rama


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 Post subject: Re: Masterworks M2894 restoration
PostPosted: Mar Thu 22, 2012 12:37 pm 
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Location: Virginia
Welcome to the ARF forums!

The Sam's Photofacts generally offer a schematic diagram, nominal voltages, alignment procedures, parts lists & a good
pictorial of the circuit board, (front and back). I've never seen them mention how to disassemble a cabinet or chassis.

Taking it apart without breaking it is half the fun! - So take your time and don't force anything.
Wish I could help you, but I've never handled that particular radio. If you get frustrated, stop and try again later.

Once you do get that puppy apart, all that it should require is to clean the bandswitch and volume control.
Personally, I use 90% isopropanol alcohol and Q-Tips from the drugstore. Cheap and very effective.
Replacing the electrolytic capacitors is recommended if its more than twenty years old. Alignment is at your discretion.

If you can post photos, we may see something you're missing.

Good luck!
~ Mitch ~


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 Post subject: Re: Masterworks M2894 restoration
PostPosted: Mar Fri 23, 2012 3:14 am 
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Joined: Mar Thu 22, 2012 4:51 am
Posts: 9
Thank you Mitch for your response and tips. Yes I am studying this carefully to find out how to take it apart without wreaking something that I may not be able to Fix. I have been watching and reading a lot about restoring radios (both tube and transistors). I used to fix radios as a kid back in India in the 70's. We are about 20 years behind the US then! I used to dream of having a hobby shop when things were way over I could afford. Now all that is history and I have been in the US for 35+ years but just started to get back to my childhood hobby....after my retirement!.

Anyway better late than never as they say and I enjoy the hobby and more than ever have the opportunity to learn and do things I could never have imagined possible some 40 years ago!
Rama


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 Post subject: Re: Masterworks M2894 restoration
PostPosted: Mar Sat 24, 2012 1:36 am 
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Joined: Oct Mon 26, 2009 10:02 pm
Posts: 2468
Location: Indianapolis, IN
Welcome to ARF, Rama !

As Mitch mentioned, posting a few interior photos might help us identify what needs to be done to safely remove chassis... At times a subassembly may need removal to gain access to "hidden" mounting screws, and there could be metal "tabs" on chassis which engage molded slots in case which requires it to be shifted or "angled" slightly to disengage...

Wish you luck with your hobby as I also got my start as a child & just re-entered it a few years ago with some of the radios I had kept for around 40 years...

Let us know your progress...

John


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 Post subject: Re: Masterworks M2894 restoration
PostPosted: Mar Sat 24, 2012 1:38 am 
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Joined: Oct Mon 26, 2009 10:02 pm
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Location: Indianapolis, IN
accidental repeat...


Last edited by xrhonda91 on Mar Sat 24, 2012 1:40 am, edited 1 time in total.

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 Post subject: Re: Masterworks M2894 restoration
PostPosted: Mar Sat 24, 2012 1:39 am 
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Joined: Oct Mon 26, 2009 10:02 pm
Posts: 2468
Location: Indianapolis, IN
Accidental repeat #2---wonder what happened ? Could moderator please remove these two mistakes ? Thanks...


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 Post subject: Re: Masterworks M2894 restoration
PostPosted: Apr Wed 18, 2012 11:02 pm 
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Joined: Mar Thu 22, 2012 4:51 am
Posts: 9
As a follow up to Mitch and John's suggestions, I am posting the pictures of the radio. I still have not figured out exactly how to take out the chassis. Any help is appreciated. This is my maiden project and hope to restore this nice looking radio. I will update as I make progress.


Attachments:
MW2894 battery holder open.jpg
MW2894 battery holder open.jpg [ 70.17 KiB | Viewed 1157 times ]
MW2894_battery holder rightside.jpg
MW2894_battery holder rightside.jpg [ 67.27 KiB | Viewed 1157 times ]
MW2894_side.jpg
MW2894_side.jpg [ 52.73 KiB | Viewed 1157 times ]
MW2894_back.jpg
MW2894_back.jpg [ 73.37 KiB | Viewed 1157 times ]
MW2984_front.jpg
MW2984_front.jpg [ 79.26 KiB | Viewed 1157 times ]
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 Post subject: Re: Masterworks M2894 restoration
PostPosted: Apr Thu 19, 2012 5:48 am 
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Try removing the nuts holding the volume/tuning/selector/etc.
I'll bet the front will come off after that.

~ Mitch ~


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 Post subject: Re: Masterworks M2894 restoration
PostPosted: Apr Fri 20, 2012 2:34 am 
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Joined: Mar Thu 22, 2012 4:51 am
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I also noticed that the screws holding the handle engages with a couple of tabs on the chassis inside. There are a couple of screws that is at the bottom which seems to attach to the battery compartment of the chassis. So this may be one of those multiple attachment points. I will give that a try Mitch and let you know.

Rama


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 Post subject: Re: Masterworks M2894 restoration
PostPosted: Apr Fri 20, 2012 2:35 am 
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Joined: Oct Mon 26, 2009 10:02 pm
Posts: 2468
Location: Indianapolis, IN
Are there screws recessed into "feet" and in handle brackets where they mount to case ? Do see two on the bottom close to each other... Looks as though the chassis & front panel will remove as a unit from the case when the appropriate fasteners are removed...

Keep us posted & good luck...

John


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 Post subject: Re: Masterworks M2894 restoration
PostPosted: Apr Sat 21, 2012 8:51 pm 
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Joined: Mar Thu 22, 2012 4:51 am
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Made progress here in getting the chassis out. It turned out to be simple with two screws on the top that holds the handle bracket and the two at the bottom that attaches to the battery compartment. The whole front slid out smoothly along with the front panel. Felt real good yesterday getting this out. See some pictures.

The real fun now begins with the trouble shooting as this radio is just dead. All it does when I plug in is a constant hiss with no response from the volume control or the band selector. Does anyone has suggestions where to focus. I did check the various voltages on the rails and they seem fine. So there is power getting to the various parts of the radio. I also checked for any broken connections but nothing obvious. I can see signs of someone been inside this radio before. All caps are Rubicon and all the transistors are the old Ge type (Toshiba mostly). I am suspecting some of the RF and IF stage transistors to be suspect as the voltages were far too low compared with the specs from service manual. Anyway this will be an interesting maiden project and I am sure many out there have lot more expertise than me so looking for any advise that can speed up my diagnosis and restoration. Thanks to John and Mitch for feedback and encouragement.
Rama


Attachments:
MW2894 back chassi.jpg
MW2894 back chassi.jpg [ 78.57 KiB | Viewed 1102 times ]
File comment: The chassis without the front panel
MW2894  front chassi.jpg
MW2894 front chassi.jpg [ 82.61 KiB | Viewed 1102 times ]
File comment: The bottom two screws holding the battery compartment was part of the 4 screws holding the cover to the chassis
MW2894 bottom screws.jpg
MW2894 bottom screws.jpg [ 47.56 KiB | Viewed 1102 times ]
File comment: The screws holding the handle (pencil pointer) was the key to removing the chassis
MW2894 top screws.jpg
MW2894 top screws.jpg [ 57.07 KiB | Viewed 1102 times ]
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 Post subject: Re: Masterworks M2894 restoration
PostPosted: Apr Sun 22, 2012 3:26 am 
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Joined: Oct Mon 26, 2009 10:02 pm
Posts: 2468
Location: Indianapolis, IN
Hello Rama,

Would clean/inspect bandswitch contacts & replace electrolytics as these are common causes of failure... Sometimes just rotating bandswitch very quickly from stop to stop will remove enough oxidation to allow it to work... How much difference do you see in those transistor voltages ? Are there electrolytic caps used in circuits where leakage could cause the problem ?

If you're getting a "hiss", the audio may be okay...

Keep us posted...

John


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 Post subject: Re: Masterworks M2894 restoration
PostPosted: Apr Sun 22, 2012 5:31 am 
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Joined: Mar Thu 22, 2012 4:51 am
Posts: 9
Thanks John for the suggestions. I have cleaned all the switches and the band switch with contact cleaner followed by gentle blow drying (no heat). I have listed some typical voltages for the signal transistors and the IF amps. The values in the () are measured vs the typical values given in the service manual.
Q1, RF Amp; C=-5.4V (-0.6), E=-3.6(-0.6), B=-3.7(-0.5), Q2 FM Mixer, C=-6.2(-0.4), E=-0.9(-0.2), B=-1.0(-0.6), Q3 FM Oscillator, C= (not given), E=-0.8(-0.5), B=-1.1(-0.8

Most of the other transistor voltage values were ok some where about 10 to 25% lower but not as bad as these. Not sure if these are due to transistor shorts or some other component causing the low values. I have read about the older Ge transistors growing whiskers and shorting etc. These signal transistors are really small TO packages as well. I was planning a systematic signal tracing but these voltages seem pretty diagnostic but I can't tell the cause..yet. Not sure if I should take out the these two transistors out of the board and test them before doing anything else.

I did not see any visible leaks or bulges by the electrolytics. Is it still good idea to replace all of these?

Rama


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 Post subject: Re: Masterworks M2894 restoration
PostPosted: Apr Sun 22, 2012 6:09 am 
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Joined: Oct Mon 26, 2009 10:02 pm
Posts: 2468
Location: Indianapolis, IN
Yes---most of the time there is no "visible" evidence of electrolytic failure in transistor radios... Sure wouldn't do anything with transistors yet---could you scan sections of schematic where they are used ? Is the RF amp transistor for the FM circuit also ? Does the gnd. lead of multimeter connect elsewhere for those voltage measurements ?


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 Post subject: Re: Masterworks M2894 restoration
PostPosted: Apr Sun 22, 2012 1:53 pm 
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Joined: Oct Mon 26, 2009 10:02 pm
Posts: 2468
Location: Indianapolis, IN
Thought about something else after last post, but not sure since I haven't even glanced at a schematic for a multi-band radio with FM for many years since my collection focus is high-perfomance early AM only sets ( with only a few exceptions )... Thinking the bandswitch "kills" the front end of FM section when other bands selected to prevent the 10.7 mHz LO from causing interference---perhaps you can examine your schematic & maybe one of the experts here will comment on this...

John


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 Post subject: Re: Masterworks M2894 restoration
PostPosted: Apr Sun 22, 2012 3:17 pm 
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Posts: 2082
Location: Sunnyvale CA
rschandran wrote:
=

I did not see any visible leaks or bulges by the electrolytics. Is it still good idea to replace all of these?

Rama


Generally, yes. These low-voltage types tend to just dry out and lose capacity. So they won't show any indications of a problem just by inspection. The smaller they are, the more likely they are to have failed, in my experience.

The brand of capacitor makes a huge difference on their reliability. The types in this radio appear to be among the more reliable. There's a fair chance they are OK, but it's cheap and doesn't take long to replace them and will eliminate one of the possibilities. The transistors from this era Japanese radios tend to be quite reliable.

Brett


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 Post subject: Re: Masterworks M2894 restoration
PostPosted: Apr Sun 22, 2012 4:54 pm 
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Joined: Mar Thu 22, 2012 4:51 am
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Thanks guys for the suggestions. I have posted the schematics. I will plan to replace all the electrolytics and see what happens before I do anything with the transistors. I appreciate the help from the forum members whose collective knowledge is just priceless :D

BTW, I find the restrictions in being able to add any file other than a "jpg" very annoying. I had to go through 3 conversions of my pdf files to get a jpg format that too in a <800x800 pixels. It took me almost 30 min to go through all this steps to be able to post two files. Not sure if this is for a good cause or there are alternatives.

Rama


Attachments:
MW2498 schematics1.jpg
MW2498 schematics1.jpg [ 93.23 KiB | Viewed 1079 times ]
MW2498 schematics2.jpg
MW2498 schematics2.jpg [ 96.79 KiB | Viewed 1079 times ]
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 Post subject: Re: Masterworks M2894 restoration
PostPosted: Apr Tue 24, 2012 9:33 am 
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Posts: 465
Location: San Diego, CA
The exact same voltage on the collector and emitter of Q1 indicates a shorted transistor. Replace it.
Rick


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 Post subject: Re: Masterworks M2894 restoration
PostPosted: Apr Tue 24, 2012 5:05 pm 
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Joined: Mar Thu 22, 2012 4:51 am
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gridleakrick wrote:
The exact same voltage on the collector and emitter of Q1 indicates a shorted transistor. Replace it.
Rick


Thanks Rick and I was thinking of the same thing. My question is whether to replace all the three or just the one. I am in the mind to replace all the transistors besides the E-lytics in the radio as I have got it all taken apart.

Also as an educational part for me, does the short in one of the front end transistors cause the immediate dependent followers (Q2, & Q3) to have much lower voltages as well. One final question is as the transistors in this radio are no longer available, are there drop in equivalents? I found the NTE quotes equivalents but not sure they are drop in. Appreciate feedback.

Rama


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 Post subject: Re: Masterworks M2894 restoration
PostPosted: Apr Wed 25, 2012 1:33 am 
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Location: San Diego, CA
"Also as an educational part for me, does the short in one of the front end transistors cause the immediate dependent followers (Q2, & Q3) to have much lower voltages as well."

Yes. The following transistors are probably good but it wouldn't hurt to test them. It would be a good learning experience for you.
Rick


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