Fisher 450T issues

cmpat

New Member
Hi Everyone,

I picked up a Fisher 450T from the thrift store a while back and am just getting around to looking at it. Upon powering it up, I get what sounds like normal audio. But after a few seconds the source fades out and a hum fades in, and I can't hear the music anymore. I replaced the large caps in the power supply with no change. Looks like one pair of output transistors is original Motorola and the other pair has been changed to a pair labeled SYL ECG.... Could mismatched outputs cause this behavior? Also I can't seem to find any info or cross reference for those Motorola, labeled 02060-7 and 01060-7. Does anyone have a suggestion there? My only test equipment at this time is a DMM, so any trouble shooting help would be appreciated. Thanks.

IMG_4707.JPG IMG_4702.JPG IMG_4705.JPG
 
Sounds like problems in the POWER SUPPLY to begin with. Check the POWER SUPPLY DC OUTPUT Voltages. Any that are out of spec by 10% need to be troubleshot, and repaired. Replace all electrolytics in the Power Supply area with 105*C rated low leakage caps (Nichicon UKL are fine). Check and replace any Zener Diodes that don't meet spec's.
 
Agreed that it is likely a power supply issue. However, it is not necessarily the output stage, especially since you replaced both main filter caps. Could be a preamp stage dropping out. Without a lot of digging into the circuit, you can start by connecting an external source (tuner or CD player) to the Tape Monitor jacks and/or taking a signal from the Record jacks to an input on another system.

Additionally, check voltages on all the other power supply points. The main supply only feeds the power amplifier stage. All other power comes from a separate supply, even a separate transformer winding. If voltages are ok, then you can connect a small capacitor (start with 0.1 µF) in series with headphones and connect between the power supply points and ground, listening for hum. There are 4 electrolytic capacitors in this supply but my copy of the manual is poor and I can't read the numbers.

Might also try to get this moved to the Fisher forum.
 
Thanks for the replies, guys. I apologize if it might take me a while to post. I have very young kids and they keep me pretty busy these days.I did have time to hook the Fisher to another receiver's Tape In and I got good clear sound from the AUX and Tuner sources. I will start trying to check the voltages you mentioned, as I have the chance. I have a free download service manual, so I'll see how far it gets me before I may have to track down an original copy. Will also inquire about moving the thread to a better location.

Also something I didn't notice before, when I listen to the Fisher through speaker outs I don't hear any source audio at all, just the hum. It's only when I listen through headphones with the speakers switched off that I can hear music for 5 seconds or so, then it will fade to hum. Not sure if this will help figure anything out, but thought I'd mention. Thanks again, will post again when I have a chance to take the cover off.
 
Hi again, guys. I'm back to the 450T after the holidays. I haven't done any more recapping, but did test voltages on the Power Supply board and found some things amiss. Terminal 9L and 9N, which are connected to the Driver board, are way off:
9L: Spec = -42V Measured = -4.8V
9N: Spec = +42V Measured = +80.8V

That's with speakers off. There is a small change with speakers on, more like -1V and +85V respectively. Together they do add up close to 42+42V = 84, so it would seem that the current is possibly being misdirected somewhere? Not sure at this point what else to check. There are some diodes nearby on the PSB, and on the Driver board side there is a resistor nearby that looks a little crispy. Unfortunately the service manual scan that I have is missing the page for the Driver board layout, so I may need to go ahead and buy an original.

One other PSB voltage that was off:
9EE: Spec = +11V Measured = +6.75V

I did also pull and test the output transistors according to the big AK thread I found, and they seem to be ok. Voltages are a little different for the original vs. non-original, but in the same ball park. Values below in case it might be relevant.
non-original pair:
Q809 (PNP): 0.56V, 0.56V, 0V, 0V, 0V
Q811 (NPN): 0.47V, 0.46V, 0V, 0V, 0V

original pair:
Q812 (NPN): 0.48V, 0.48V, 0V, 0V, 0V
Q810 (PNP): 0.53V, 0.52V, 0V, 0V, 0V

Any further advice is appreciated.... Thanks
 
Rebuild the power supply board. Resistors, Zener Diodes, diode Bridge (4 diodes), and caps. FISHER ran these extremely HOT and they literally cook themselves to death. Get the power supply voltages correct 1st and then worry about the rest. Thisi s common practice Bets are after the voltages are in line, a lot of the downline problems will go away. But you'll need to check the rest of the boards anyway. 9EE is probably due to the Zener diode (CR957 15v 3w) being shorted among other things. The power supplies were fairly tough for the era, but they haven't aged well in a lot of cases. It's like that old saying "She fell off the top of the FUGLY Tree, and hit every branch on the way down!"

If you got the HIFIEngine manual, I agree it's for shit. Rick Stout at www.stereomanuals.com has repop's for the 450-T. NO AFFILIATION! 90% of the manuals I've bought or gotten over the years have come from Rick, whether, FISHER, PIONEER, Sansui, etc. All have been reproductions. Most are better than the originals. Clear drawings, legible writing, extraneous pixels removed, schematics are not cut into pieces. And to me I can read them without my glasses. Schematics are usually single sheet and are good enough for enlargement @ Office Depot or Staples on a 36" x48" Sheet. They do get pricey tho at times. He combined 2 manuals that were produced for the 450-T and it's export versions the 395-T, and 505T. So it's quite large @ 96 pages. The price code is G-19 which is $27.00 plus 6.00 for priority shipping. Sure it's pricey, but you'll not get a better manual, even an original. The original will have faded paper, water spots, and generally a poor attitude to age.

Ultimately it's up to you. How motivated are you to rebuild the 450-T, and is the 450-T worth the $33.00 for a manual ?

The 500-TX uses the same basic amp module so you can use that for wiring points and possibly parts. The suffix on the number is different ( 1 off) but the main part number is the same. I wouldn't have any problem using the 500-TX schematic for the board. HIFI's copy is one I scanned from a copy from Rick. It's a real good scan.
 
.....
voltages on the Power Supply board and found some things amiss. Terminal 9L and 9N, which are connected to the Driver board, are way off:
9L: Spec = -42V Measured = -4.8V
9N: Spec = +42V Measured = +80.8V
.....

I assume that these voltages are measured between the points indicated and ground. If so, you have a HUGE problem with a bad ground someplace, possibly the power transformer center tap lead itself, and that +80.8 V could very well have blown up a few things.
 
Hey Larry & Fred, thanks for the info.

Yes, for voltages I measured between the points and chassis ground.

Re: the question of how much effort & expense it’s worth to fix up, I’d say some for sure. Being a thrift store purchase I haven’t invested too much yet. If it’s a matter of buying a quality manual and rebuilding a board or two, I say ‘Yes’. It did have a nice rich sound to it when I ran the preamp through another receiver, plus looks cool too. If it’s a worst case scenario like bad transformer, then I’ll have to think on it and look into the available options. Not sure which to attempt first: (learn how to) test the transformer, or pop in some diodes, etc. and see if the issue clears up.

Larry, yeah, thanks for catching my typo on the transistor tests. I was referencing the same thread as you, but testing in the order mentioned in post #1. Where I listed 0V should actually be OL or no reading. Going in the order of post #11, and working from Left to Right on the board, I get:

Non-original pair:
Q809: 0.56V, 0.56V, OL, OL, OL, OL
Q811: OL, OL, 0.45V, 0.46V, OL, OL

Original pair:
Q812: OL, OL, 0.48V, 0.49V, OL, OL
Q810: 0.53V, 0.53V, OL, OL, OL, OL

Again, I appreciate it. Looking forward to hearing how you guys might proceed on this.
 
Those transistors are fine. The transformer sounds to be working fine as your preamp section is working . Contact Rick and get the manual. Once you get that, start it up and take voltages on ALL PINS on the power supply and shut it down again. Like I said in the previous post, I'm betting the power supply is toasted and a rebuild (including the Main Filter caps)should get the voltages back in spec. Once that is done you can start on the Main Amplifier and work back to the EQ/Phono board.

On the 1uf 70V lytics, use a Cornell Dublier DME series Film cap 1uf 100V. Do this on all boards that spec them. These are the GREY PLASTIC coated lytics with the value/voltage stamped into the top as so: 47/100. On the Power supply us Nichicon UPW or UHE series low impedance caps and for the rest use UKL Series Nichicon lytics. Bump the voltage up 1 or 2 values. This is because the all voltage is higher today, and the B+ voltage is less than 5 volts below the cap voltage in most circuits. When you put it on todays voltages the original caps are overvoltaged and stressed, leading to a "blowout" in a lot of cases. If it's a 6v cap, a 25v is ok. I use 50V caps from most everything except for the 6V. and the 100V for the 70V.

The Main caps are kind of weird. This is what I got off the manual. DOUBLE CHECK with VISUAL VERIFICATION. C954 is a 2000uf 55V. Use a 3300uf 80V. C955 is a 500uf/80V use a 1500uf/100V . The DIODE Bridge (FISHER used individual diodes here) use a 1n or uf 5406. C956 looks like a 2000uf @ 55V OR 65V (visually verify!) Use a 3300uf 80V
and the C960 is 1000uf/40v use a 2200uf 63v.

Zener diodes are a bit tricky. CR957 is 15V 3W (Use a 15v 5W).CR966??? is a 36V 2W (use a 36V 4W here). Use 1/2w resistors (metal film) for resistors that have no wattage marking. The larger resistors that have blackening of the board under it, double the wattage and mount it OFF the board about 1/4"-3/8" . CR955 use a 1n or UF 5406.

Remove the transistors 1 by one and do the 6 way test. Mark it and the board for orientation so you can put it back if ok.

ALL PARTS can be gotten @ mouser Make up a list for the parts to be bought and post it. Either Fred or I will vet it. Then you can get it all in one shot. Make note of the part# from the board

FOR EXAMPLE
Board part, value/voltage., New part. .Mouser part #
CR955 SID51C052-19 1n5406. 863-1N5406RLG

Larry
 
To test the power transformer, disconnect all the secondary leads. Apply primary voltage and measure all secondaries INCLUDING the center tap on the main secondary. That winding should measure approximately 30 V between each red wire and the red/yellow center tap. This part of the supply is not used by the preamp, so a working preamp does not verify this supply.

If the transformer is ok, then, as Larry says, rebuild the power supply board completely. It will not be that expensive, maybe $10-20 plus the main filter capacitors. Make sure those ground connections are good, especially where the transformer center tap is connected to the chassis.
 
Ok, I made some progress. In doing the transformer test I was getting around 63V between the 2 red wires, but when I tested between the red and the center tap I was getting between 1 and 10V per side, and these numbers would change some whenever I repositioned the multimeter clip. Seems the culprit was the clip on the end of the center tap lead: I guess it was grabbing mostly insulation and not making good contact with the wire itself. I pulled the clip off, exposed some wire, checked voltages and got 32V per side. I had broken the clip pulling it off so I soldered the center tap wire back to the post. Put all the transformer wires back, and checked power supply voltages. 9EE is still reading low, around 6V, but looks like 9L and 9N are now sitting close to where they should be, +/- 42V.


I decided to fire it up, and what do you know, it works, though not perfectly. Ran it for about 5 minutes and the heat sink on the outputs was too hot to leave my finger on it. Also made a loud pop/crack through the speakers when I turned it off. Do you guys still recommend rebuilding the power supply in this case?
 
Rebuilding the power supply is not going to hurt, but it appears there is a problem in or around the output stage if the heat sink is getting too hot to touch in normal use. Unfortunately, the service manual at my disposal does not show the power amplifier itself, so I may not be able to help much unless you can find a schematic.

Getting the ±42 V where it should be is a big step, so it is not floating all over the place.
 
FRED; Pull the 500-TX manual from hifi engine for now. The board main number is the same with a diff suffix. That should suffice until the op gets a manual from Rick Stout
 
Hey guys, yeah I've been using the Hifiengine manual that's missing the page for the power amp. I can go ahead and order a complete manual. I notice that the 500-TX manual has instructions at the beginning for setting idling current, etc, which the 450-T manual doesn't seem to have. Lots of info on the auto tuner but not much on the amp itself. Would the bias procedure be the same?

Here's a closeup of the output schematic from my manual (unfortunately a little fuzzy), if it helps for anything. The only specs I see are the 240mV from the preamp and the 21.9V, is that to the speaker selector?
 

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cmpat; The 21.9v is the MAX AC voltage that the amp is capable of putting out to the speakers. The 240mv is the input from the preamp section. The +42V and -42v are the Main Rail voltages. FISHER used the same basic amp in more than 1 receiver with minor differences. Hence the suffix #.

For Example if you look at the 250-T/400-T manual, the 250-T and 400T use the same board (between them) but the output devices on the 250-T are TO-220 and the 400-T uses TO-3 devices. The main difference between them is the output devices and the Rail voltages and uprated drivers to handle the higher input voltages of the 400-T. It's possible that the 450-T and 500-TX, using the same basic board(but with a different suffix) are close enough that you could use the 500-TX for basic troubleshooting, but that's as far as I would go unless you check the board for each and every part and and voltage both in and out, and compare them with the 500-TX board. If everything matches (and I do mean everything) you could try the bias instructions while on a DBT (after marking the original positions). If you can get the idle and offset to spec on the DBT and you don't get smoke or an explosion of parts:biggrin:, then it's probably ok to try it again on wall voltage. DO NOT set idle and offset on the DBT and then go straight to the wall. RESET the pots back to original positions 1st.

Please DO get the 450-T manual so you have an accurate, CORRECT MANUAL. Rick is the BEST source for them, even tho it does cost. Every one of my FISHER and PIONEER units that is a keeper has a manual from Rick. Even my consoles. It gets expensive after a while but I get a manual without all the scanning crap and fuzziness that comes from 3rd,4th.5th generation scans and copies. Most of the copies out in the 'net come from a few sources, but all of them (I'm talking about a FISHER 400 manual with all the crap, tech writing, owner notes on it, etc.) have all the same mistakes and junk on them. Some are 10th generation copies and quite poor(and these are from guys looking to make a buck even on E-prey). Rick's repops are all 1st gen from the originals, then cleaned up for extraneous crap on them, voltages, values, and part #'s are double-checked and made correct if necessary. They get scanned on Professional quality photo scanners, not consumer quality scanners everyone has at home. They are then checked again and any bloopers are removed and corrected, then the original is scanned again. Schematics are scanned to fit 1 or 2 11x17 sheets with folds as original. Scanned pages are single sided, vs. doublesided, with the back side on it's own sheet. Heavy Card Stock is used for the covers. When the inside pages are correct, it's all staped using 4-5 staples on the edge, and this is re-inforced with Duct tape along the spine. He leaves enough room so you can use a 3 ring binder punch and install them in a binder. Again, I'm not affiliated with Rick or his Co. I am a long time and extremely satisfied customer.

Larry
 
.....
Here's a closeup of the output schematic from my manual (unfortunately a little fuzzy), if it helps for anything. The only specs I see are the 240mV from the preamp and the 21.9V, is that to the speaker selector?

Those numbers are in boxes, indicating that those are not measured static voltages. They are signal voltage at that point for maximum output.
 
.....
If everything matches (and I do mean everything) you could try the bias instructions while on a DBT (after marking the original positions). If you can get the idle and offset to spec on the DBT and you don't get smoke or an explosion of parts:biggrin:, then it's probably ok to try it again on wall voltage. DO NOT set idle and offset on the DBT and then go straight to the wall. RESET the pots back to original positions 1st.
.....

I'd actually set bias to minimum after the DBT test just to be safe. The original position could be too high. With the twin ±power supply, I don't think there is an offset adjustment. If there is excessive DC on the output, then there is a problem.
 
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