Author Topic: 200A - low volume after recap/transistor replacement  (Read 262 times)

Offline sonoflee

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200A - low volume after recap/transistor replacement
« on: September 13, 2017, 07:56:24 PM »
I have an old wurlitzer 200A that has been sounding noisier and noisier over the years, so I decided to spruce it up a bit.  Rerouted wiring, replaced the neon bulb with an LED, replaced all the electrolytics, replaced some resistors, and got a new set of transistors.  One package of transistors was mislabeled (and I didn't double check the label on the transistor), so I ended up installing the wrong one in TR10 - it was a PNP where an NPN was supposed to go, so it blew up and took one of the onboard fuses with it.   

Replaced transistor (and fuse) with the correct one eventually, and it works again... but the volume is way too low.   It's quieter than a regular speaking voice at max volume, so quiet I have to put my head close to the speaker to be sure it's working.  When you max out the tremolo knob, it gets a bit louder, but not much. 

At this point, I'm pretty stumped and looking for advice on what to test next. I'm good with a soldering iron, but not the best at troubleshooting a circuit. I did go through and pulled test values to compare everywhere I could find them on the schematics - I'll add those below in case they might help.  Thanks for reading!

transistorPointschem. valuetested value
TR1E1.952.09
B2.452.63
C4.14.26
TR2E3.43.6
B4.14.2
C8.88.4
TR3E0.680.65
B1.251.21
C5.9(varies)
TR4E00
B0.680.65
C5.9(varies)
TR7E0.640.61
B0
C-22-24
TR8E0.640.61
B0
C-22.5-25
TR9E-0.65-0.57
B00
C0.570.5
TR10E0
B0.650.5
C2224.36
TR11E22.524.4
B2224.4
C
TR12E0
B-0.65-0.57
C-22-24.6
TR13E-22.5-24.87
B-22-24.6
C00
TR14E-22.5-24.7
B-22-24.15
C-0.65-0.56
TR15E0.961
B1.51.56
C43.8
TR16E2.92.6
B43.8
C7.78.12
TP191514.42
22.524.4
TP18150150.6

Offline pianotuner steveo

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Re: 200A - low volume after recap/transistor replacement
« Reply #1 on: September 22, 2017, 07:28:35 PM »
Have you tried unplugging the reed bar and temporarily testing the jack with audio from a phone, iPad, etc? This will tell you if the problem is in the amp or reed bar ( unless there is a problem in both places)

If the amp works with this test, check the reed bar voltage. Be careful, it's about 150vdc...
1960 Wurlitzer model 700 EP
1968 Gibson G101 Combo organ
1975 Rhodes Piano Bass
1979 Wurlitzer 206A EP
1980 Wurlitzer 200A EP
1980 Wurlitzer 270 Butterfly Grand
2000 Yamaha acoustic piano
2004 Hammond XK3
2009 73A Rhodes Mark 7
2009 Korg SV-1 73
....and a few guitars...

Offline tjh392

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Re: 200A - low volume after recap/transistor replacement
« Reply #2 on: September 23, 2017, 03:39:40 AM »
The 200a is the one with without the audio jack to the reed bar it's a push connector fit to the PCB.

Also worth mentioning that on a 200 the phono to the reed bar has a fair bit of voltage so it's best not to connect your iPhone. Someone else on the forum suggested on a 200 that you should use the unused mic input.

Anyway getting back to it, could it be that the mislabelled transistor took some of the others out with it?
Rhodes Stage 73 1975 with Satellite System, Wurlitzer 200a 1976, Hohner String Performer

Offline pianotuner steveo

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Re: 200A - low volume after recap/transistor replacement
« Reply #3 on: September 23, 2017, 08:15:31 AM »
The voltage for the reed bar does not come out of the phono jack input on the board when you unplug the reed bar. Or at least it shouldn't since this is an audio input... It is wise to test to make sure there is no voltage there before plugging in an external audio source, but the voltage comes from the reed bar preamp if I remember correctly.

Are you 100% sure that ALL 200A's have no RCA jack? I thought the earlier ones still had the RCA? Or is my memory shot?  I rarely ever work in Wurlitzers anymore and it's been years since I've opened a 200A. I worked on 1 145 last year and haven't seen another since...
1960 Wurlitzer model 700 EP
1968 Gibson G101 Combo organ
1975 Rhodes Piano Bass
1979 Wurlitzer 206A EP
1980 Wurlitzer 200A EP
1980 Wurlitzer 270 Butterfly Grand
2000 Yamaha acoustic piano
2004 Hammond XK3
2009 73A Rhodes Mark 7
2009 Korg SV-1 73
....and a few guitars...

Offline sonoflee

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Re: 200A - low volume after recap/transistor replacement
« Reply #4 on: September 25, 2017, 08:21:12 AM »
Thanks for the suggestions!

testing the preamp vs amp is definitely worth trying, steveo. I'll test for voltage and give that a shot with an old cd player or something rather than an iPhone just in case there are any issues, then report back.

tjh392: that was my thought too, but I've removed and tested all of the other transistors out of circuit and they test OK.  tested most of the caps and they also seem fine, and I'm not seeing any obvious damage elsewhere.  Reflowed a bunch of solder joints this weekend and no change - it sounds really good when it's on, but just has really low volume.

If any other ideas come to mind, please keep them coming!

Offline cinnanon

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Re: 200A - low volume after recap/transistor replacement
« Reply #5 on: September 25, 2017, 08:33:44 AM »
 I'd go with a new amp.  Just think how much time you can / would have saved! I'm surprised nobody has come up with an amp kit by now. Solder by numbers.

Offline pianotuner steveo

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Re: 200A - low volume after recap/transistor replacement
« Reply #6 on: September 25, 2017, 02:22:36 PM »
Not everyone has the extra money lying around to just pop in a new amp. I've been wanting to get one for a few years, but other things come up that are higher priority such as sudden brake failure just last week for example.

Does your amp board have the trim pot? If so, us it turned down?
1960 Wurlitzer model 700 EP
1968 Gibson G101 Combo organ
1975 Rhodes Piano Bass
1979 Wurlitzer 206A EP
1980 Wurlitzer 200A EP
1980 Wurlitzer 270 Butterfly Grand
2000 Yamaha acoustic piano
2004 Hammond XK3
2009 73A Rhodes Mark 7
2009 Korg SV-1 73
....and a few guitars...

Offline cinnanon

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Re: 200A - low volume after recap/transistor replacement
« Reply #7 on: September 25, 2017, 07:58:42 PM »
I think that though transistors test OK, they can still function improperly under load

Offline sonoflee

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Re: 200A - low volume after recap/transistor replacement
« Reply #8 on: September 25, 2017, 08:10:23 PM »
Thanks for the additional ideas! I would love to buy a new amp, but it's not a financial possibility right now. 

Good news: Just checked it out with a cd player and my phone playing a test tone (400hz sine wave) into the amp, and it's WAY louder through the speakers...  Before I start digging into the preamp as the culprit, is the headphone out of my phones/ancient discman at an appropriate level (compared to the level of a working preamp out) to test this, or do I need to use a line level source?  If it matters, it was plenty loud even with the phone/cd volume very low.

Thanks!

Offline pianotuner steveo

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Re: 200A - low volume after recap/transistor replacement
« Reply #9 on: September 26, 2017, 07:09:07 AM »
If you haven't done so yet, look up the correct schematic for your model- amp and preamp. I think you are missing the voltage to power the reed bar.

Since the  amp works, the next step is to see if the reeds are getting their 150vdc. (It can vary a bit, but it should be pretty close) be careful. When I was a teen and didn't fully understand the powered reed bar, I got zapped a few times!  Even though it's D.C. It's still a lot of voltage. What I would do next is take the reed bar preamp Pcb off ( with the power off!) and inspect it for cracks, broken traces, bad (cold) solder joints. Repair anything that looks suspicious.

I'm not sure why you are asking about a line level source. You have determined that the amp works fine.
1960 Wurlitzer model 700 EP
1968 Gibson G101 Combo organ
1975 Rhodes Piano Bass
1979 Wurlitzer 206A EP
1980 Wurlitzer 200A EP
1980 Wurlitzer 270 Butterfly Grand
2000 Yamaha acoustic piano
2004 Hammond XK3
2009 73A Rhodes Mark 7
2009 Korg SV-1 73
....and a few guitars...

Offline sonoflee

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Re: 200A - low volume after recap/transistor replacement
« Reply #10 on: September 26, 2017, 08:51:35 PM »
I learned my lesson about the reed bar when I was younger as well!

Tested tonight, it read ~ 131 vdc at the reed bar, and 143 vdc at the "+150 V" test point on the amp.  Is that within range, or too low?

I went through the preamp pretty thoroughly & reflowed all the solder joints last weekend, and didn't find any cracks or breaks.

Offline cinnanon

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Re: 200A - low volume after recap/transistor replacement
« Reply #11 on: September 26, 2017, 09:16:40 PM »
Not everyone has the extra money lying around to just pop in a new amp. I've been wanting to get one for a few years, but other things come up that are higher priority such as sudden brake failure just last week for example.

Well then I'm tapping out!  My amateur electronics knowledge won't do this thread much good.  Even VV doesn't repair these amplifiers. Godspeed!

Offline pianotuner steveo

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Re: 200A - low volume after recap/transistor replacement
« Reply #12 on: September 27, 2017, 08:59:59 AM »
I'm more of a piano tech than electronics tech, but that seems to be within range to me. Does anyone else have any suggestions?  It really sounds like it is in the preamp now since you said the amp works. The preamp board grounds to the reed bar with its mounting screws if I remember correctly. Have you checked to be sure it is grounded?
1960 Wurlitzer model 700 EP
1968 Gibson G101 Combo organ
1975 Rhodes Piano Bass
1979 Wurlitzer 206A EP
1980 Wurlitzer 200A EP
1980 Wurlitzer 270 Butterfly Grand
2000 Yamaha acoustic piano
2004 Hammond XK3
2009 73A Rhodes Mark 7
2009 Korg SV-1 73
....and a few guitars...

Offline sonoflee

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Re: 200A - low volume after recap/transistor replacement
« Reply #13 on: October 12, 2017, 09:59:14 AM »
Just an update - I ended up buying a never-used Vintage Vibe preamp on ebay for pretty cheap, and everything's back to the correct volume.  I think that there must have been a broken trace on the old preamp that I just couldn't find.  Thanks to everybody, especially pianotuner steveo, for the help!

Offline pianotuner steveo

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Re: 200A - low volume after recap/transistor replacement
« Reply #14 on: October 12, 2017, 07:34:16 PM »
No problem, that's why we're here... I  hope you didn't through out your original preamp, it can be repaired..... or sell it as is to someone who can repair it....
1960 Wurlitzer model 700 EP
1968 Gibson G101 Combo organ
1975 Rhodes Piano Bass
1979 Wurlitzer 206A EP
1980 Wurlitzer 200A EP
1980 Wurlitzer 270 Butterfly Grand
2000 Yamaha acoustic piano
2004 Hammond XK3
2009 73A Rhodes Mark 7
2009 Korg SV-1 73
....and a few guitars...