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Author Topic: [SOLVED] Rowe R-88 Phono power supply repair info needed  (Read 3159 times)

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Mark Barnes

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[SOLVED] Rowe R-88 Phono power supply repair info needed
« on: July 09, 2020, 12:07:52 pm »
I'm helping out a friend with a Rowe R-88 phonograph jukebox. 
The phono power supply unit is providing +8 VDC, +28 VDC, but is not providing 28VAC.
I've disassembled the phono power supply unit, and the transformer windings produce good AC voltages.
Looking at the circuit board for that PSU circuit board, P/N 60887301 (which we have reason to believe the entire PSU is actually from an R-84 or R-85 unit), I identified one small TO-92 transistor as shorted.  There are three small TO-92 transistors on the board.  Out of circuit it's shorted, and a component tester read it as a 75-ohm resistor (that's how bad it is).
The transistor has a National Semiconductor logo, and is numbered "927" on top, then "S300H" and has the emitter, base, and collector pins labeled.  I've googled and I'm not coming up with what this is.  The other two small transistors have a different marking, "922" and then the same "S300H". 
I'm looking for any information I can get on this.
If there is a schematic for the P/N 60887301 circuit board,
or an identification of what the "927" National Semiconductor transistor is, or any suitable substitute.





« Last Edit: September 06, 2020, 08:15:32 pm by Mark Barnes »

Ken Layton

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Re: Rowe R-88 Phono power supply repair info needed
« Reply #1 on: July 10, 2020, 10:48:26 pm »
From the Rowe # 3-65355-11 (June 1985) R-88 Shop Service Manual:

Should have Rowe # 6-09357-01 Power Supply Assembly in it.

These transistor locations cross to these part numbers:

Q501 and Q502 are NPN. Rowe # 7-00311-01. Motorola # MPSU01A. National Semiconductor # NSDU01A. RCA # SK3199.

Q503 is NPN. Rowe # 7-00300-08. Motorola MPSA06. RCA SK3479. Old Rowe # S300H.

The SHOP service manuals have not been reproduced. They are double sided 11 x 17 (NOT folded) pages throughout the manual (approx 100 pages). The last couple of pages give reference numbers from Rowe numbers to what the exact generic part is. These SHOP manuals were very expensive back in the day because only Rowe distributors could afford them.
« Last Edit: July 10, 2020, 11:09:03 pm by Ken Layton »

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Re: Rowe R-88 Phono power supply repair info needed
« Reply #2 on: July 11, 2020, 10:18:15 am »
Ken, THANK YOU.  That's awesome info.

So this R88 definitely has had its phono PSU replaced with one from an R84/R85, part number 6-08873-01.  The transistor in question that I'm working with is Q503.  It looks like boards 6-08873-01 and 6-09357-01 use either the same circuit or nearly the same circuit but with a different layout.  Transistors Q501 and Q502 look bigger and beefier on the 6-09357-01 board, but Q503 appears to be the same on both.  From your information I was able to find suitable replacements, including the Fairchild 2N5551 with the same current rating and greater voltage handling and similar gain. 

If you possibly have the schematic for the 6-08873-01 board from the R84/R85, is that something you can share?  I'd like to be able to work off the manufacturer's schematic if possible, but as this is a single-layer board I can trace it if I have to.

Again, THANK YOU for your help with this.

Ken Layton

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Re: Rowe R-88 Phono power supply repair info needed
« Reply #3 on: July 11, 2020, 10:57:40 am »
Sorry, I don't have schematics for any R84 or R85 boards.

I own "shop" manuals for the R88/R89 and the R90/R92 jukes. The shop manuals have schematics to all the boards. It wasn't until the CD100 series that Rowe started including all board schematics in the "field" manuals.

John Robertson at flippers.com has made his own list of Rowe transistor cross references here:

https://www.flippers.com/pdfs/ROWE-AMI_TRANSISTOR_CODES.pdf

I think you'll find it most helpful.
« Last Edit: July 11, 2020, 11:01:43 am by Ken Layton »

Mark Barnes

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Re: Rowe R-88 Phono power supply repair info needed
« Reply #4 on: July 12, 2020, 12:05:43 pm »
Thanks for that link to the cross references.
The components for the R88 photo PSU looks almost identical to that on the R84 board.  I think a schematic for the R88 board would still be very useful to me for putting this R84 board back into service.  Would have have a scan of that R88 board schematic?

Mark Barnes

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Re: Rowe R-88 Phono power supply repair info needed
« Reply #5 on: September 06, 2020, 08:15:02 pm »
Solved the problem of the missing 28 volt AC line.
The 28 volt secondary winding from the transformer comes into the circuit board on two pins.  One of the two pins is tied to ground.  The other ties to the pin that 28 volts AC goes back out of the board on.  So. . . there's not a whole lot of places where it could be getting sucked down.  All the 28 volt AC line does on the board is go through a diode to half-wave rectify it to around an average of 13 volts DC, then goes through a dropping resistor to the red LED that lights up indicating the 28 volt AC line is good, with the cathode grounded.  (That LED was of course out.) 

It was out because the LED itself was shorted.  Lifting a leg on the half-wave rectifier diode brought back the 28 volt AC line, and replacing the LED fixed the problem.
Yeah, the LED that indicates 28 volts AC was bad, causing the 28 volt AC line to drop down to around 17 volts AC.  That's all it was.

Of course, that Q503 transistor was shorted; not sure what its purpose is without a schematic, but the Fairchild 2N5551 replacement is a suitable replacement and doing fine in the circuit. 

While I was in there I re-capped the entire board with new caps.  There's two large electrolytics and three small 2.2 uF electrolytics.   The large electrolytics showed signs of overheating and swelling, so re-capping seemed like a prudent step. 

This jukebox has definitely been retrofitted at some point in history with the older R84/R85 power supply, but it apparently works, so this job is officially complete.

Ken Layton

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Re: [SOLVED] Rowe R-88 Phono power supply repair info needed
« Reply #6 on: September 06, 2020, 09:21:19 pm »
For me, I don't think I've encountered a shorted conventional LED, but it does happen. I always keep several types/colors of conventional LEDs  around for replacement/repair jobs when I find bad ones.

Mark Barnes

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Re: [SOLVED] Rowe R-88 Phono power supply repair info needed
« Reply #7 on: September 07, 2020, 04:56:31 pm »
Yeah, it's a first for me too.  I've never run into a shorted LED before.  The simplicity of that leg of the circuit made it really easy to just mentally deduce what must be wrong with it.  It was easy to test the secondaries of the power transformer since its wires all go to a connector.  It was simple to just disconnect the connector and measure the secondary outputs with them out-of-circuit.  Once I knew I had the 28 volts AC on the transformer, it was pretty straightforward to work out the problem since it literally does nothing on the board other than light the 28 v.a.c. LED.