tonyj
Junior Member
Jukebox Newbie
Posts: 93 
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Post by tonyj on May 18, 2021 20:03:05 GMT
If the bottom device is a diode, getting resistance readings in both directions isn't typical for a standard diode. One way should indicate open as it should be reversed biased IMO
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TCW
Full Member
Indianapolis, Indiana USA
Posts: 222
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Post by TCW on May 19, 2021 17:28:24 GMT
I think its for voltage regulation in biasing and not a standard diode. - Tom
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Post by Ron Rich on May 19, 2021 18:12:35 GMT
Tom,
Hint:-- It ainna "diode" ! Ron Rich
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TCW
Full Member
Indianapolis, Indiana USA
Posts: 222
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Post by TCW on May 20, 2021 13:50:00 GMT
Ron.
Ok its not a (stabistor) Forward Reference Diode or Forward Regulating Diode or Switching Diode. I thought its use is voltage regulation or stability. It appears to be a silicon device in glass. It sure would help if it had something written on it. I have an amp laid up waiting for me to figure it out and I don't know what it is or a spec to replace it with. What do you know?
Tom
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Post by Ron Rich on May 20, 2021 13:54:53 GMT
Hi Tom,
Nope-- not a "stabistor", if connected to the white wires. Ron Rich
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TCW
Full Member
Indianapolis, Indiana USA
Posts: 222
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Post by TCW on May 20, 2021 16:32:56 GMT
Yes, its connected to the white wires... some sort of variable resistor? If so, what varies it. Heat, current? And most importantly, what's the part number???  |
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Post by Ron Rich on May 20, 2021 21:19:09 GMT
Tom,
Where did you find that-- The 4 on the right are a symbol for a tri-stabistor, and a diode. The one on the left is a symbol for a thirmistor-- in this case a 10 k, 10% one-- which looks to be OK to me, from whut you rote--- ?? Ron Rich
Ron Rich
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TCW
Full Member
Indianapolis, Indiana USA
Posts: 222
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Post by TCW on May 21, 2021 4:50:24 GMT
I found it in my 93 manual in Section 5 regarding the preamp single line drawing. Unfortunately the quality of the image like the entire manual is pour. I can't tell you what the letters are next to the symbol (maybe a #t but it should be +t°) but I did expect to see more of a hockey stick shape when expressing a thermistor symbol, not an arrow.  This looks like a good candidate. rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F332969556601 |
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Post by Ron Rich on May 21, 2021 17:15:59 GMT
Tom,
Attsa why I said in the Hi Newbies post--BUY, the manual-- do not try to use poor quality "downloads"
That's a pos thirmister-- see the "errors known" post, in the FAQ's section. Ron Rich
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TCW
Full Member
Indianapolis, Indiana USA
Posts: 222
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Post by TCW on May 21, 2021 21:23:08 GMT
Ron, You are correct. "ROWE Ami: All of their service manuals contain MANY errors/omissions-- way too many to doc. here ( I have the 17th printing of the WP 100 manual, which still has errors in it ) !! One of the most glaring is in the amplifier sections of the manuals starting around the R-93, all through the CD's as far as I can tell- Many show the biasing diode section as a single diode-some show it as a stabistor, others show it as a tri-stabistor ( 1N4157), some show it as the tri-bistor, plus a single diode (1N4148)in series, and others show a pos thermistor (Rowe # 70037004-- P-10 k, 10% ) connected between pins one (white wires) on both Darlington outputs. The last version is correct --Tri, in series with the diode & thermistor." As far as the printed manual I would recommend buying from a source known here and listed in the FAQ. Before becoming a member I ordered a paper copy and got a print of a poor quality PDF for my efforts and hard earned money. Some people think good enough for them should be the standard for you as well.  Tom |
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TCW
Full Member
Indianapolis, Indiana USA
Posts: 222
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Post by TCW on May 24, 2021 21:28:12 GMT
I think the newest Rowe CD machine we had on our route was a "F". We only had one of that model and the title pages were always breaking. I have never encountered any of the Rowe amplifiers with the self adjusting bias driver boards. Your pictures and parts listing will certainly help others with those boards. Information about them is very sparse out there. Thanks for posting.  If I had to guess what your problem might be, it could be a leaky diode. Hey Ken, Just curious, was your hunch on it being a power diode or something on the driver board itself? - Tom |
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Post by Ken Layton on May 25, 2021 4:59:45 GMT
On the driver board.
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TCW
Full Member
Indianapolis, Indiana USA
Posts: 222
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Post by TCW on May 26, 2021 13:19:48 GMT
Ken,
Correct, When I was pulling Q7, an MPSA56, the emitter leg stayed behind. Due to an over active of imagination I pulled Q10, a TIP31C. it was fine. I did some more checking. You know how you check diodes in circuit and some will conduct in both direction due to circuit conditions (design). I compared my findings to a good board and several on the damaged board didn't conduct in both directions. What that said to me was something was open. It wasn't even discolored, R26 was open. This is wired directly to the base of Q7 so no surprise other than there was no visible damage.
What I found on the driver board that had failed:
Q7, an MPSA56
R26, 180Ω
R29, 180Ω
R30, 470Ω
Tom
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