Fidelity transistorised Playmaster - reverse engineering? - Page 7 - UK Vintage Radio Repair and Restoration Discussion Forum

Borderer · 3rd Jan 2023, 8:03 pm

Ben, Following this with interest, although I no longer have the machine.

Diagram in post 18 is for a different machine. Not sure it is the same. From memory, the Fidelity was positive to chassis but someone else will be able to confirm.

Photos in post 1 and 105 show the rectifier location at the RH end of the board and you can make out the rectifier connections.

The 16 volts that you have must be at the input to the rectifier - the heater and HT of course come direct from the transformer.

ben · 3rd Jan 2023, 9:03 pm

Thanks. Replaced missing rectifier bridge, 1000uF smoother (+ve gnd), replaced missing 1000uF cap on output stage. Replaced 1x 25uF/25v cap which had leaked and had leg hanging off.

Now there is hum and a slight crackle from speaker if volume adjusted.
If REC selected green segment in magic eye lights up, but just as one dull blur.

So, some progress but still not operational. Will keep at it.

DMcMahon · 3rd Jan 2023, 9:13 pm

Quote:

Originally Posted by Chris55000

I've just checked "up top", & I'm thinking you'll find the "Playmaster TR8" or the "Playmaster TR9", both of which you can buy "up top" will meet your needs

Should not Playmaster above have read "Playmatic ?

David

DMcMahon · 3rd Jan 2023, 9:27 pm

Quote:

Originally Posted by ben

Perhaps someone reading this could confirm something. From the diagram in post 18, am I to assume that the positive output from the rectifier is in fact fed to chassis and the negative to the output stage? Or is that diagram for a different setup?

Since the entire rectifier was removed and there are no board markings, I'm largely in the dark.

+ve ground and -ve to the supply rail on the Fidelity Playmatic TR8/TR9 schematic, with -24V at reservoir capacitor C27.

The TR8/9 are a 2 valve hybrid with EM87 Magic Eye and ECH83.

David

Chris55000 · 3rd Jan 2023, 9:41 pm

. . .Oh dear, I'll have to get those Playmaster remains out from under my bed and get on with some more drawing–out me thinks – (it got put on one side because of holidays, eye–surgery, repair work for another Member, now complete), and the panel I got being only part–complete, hence me having to puzzle some of it out still!

Chris Williams

ben · 28th Nov 2023, 11:15 pm

I recently looked at my moribund unit again. A dodgy design to begin with and an example which had missing parts and had been got at -a glutton for punishment am I!

One of the output pair was s/c, I replaced the AC128 and AC176 with an AC187 /AC188 pair which I had to hand, now there's quite a strong output but the signal is of terrible quality, very distorted/fuzzy and a bit of buzz. The winding for track 1 of the R/P head is o/c, so am awaiting a suitable replacement. Erase does not work. For all I know the erase head may be open too!

The odd display on the EM87 was due to a green (signal?) and a yellow wire having detached themselves from the pcb. Now when Rec is selected the display is a bit jittery, but not blurred.

I will do some more tests on the resistors and erase head if/when I get a new R/P head.

3rd Jan 2023, 8:03 pm	#121
Borderer Tetrode Join Date: May 2009 Location: Hereford, Hereford and Worcester, UK. Posts: 93	Re: Fidelity transistorised Playmaster - reverse engineering? Ben, Following this with interest, although I no longer have the machine. Diagram in post 18 is for a different machine. Not sure it is the same. From memory, the Fidelity was positive to chassis but someone else will be able to confirm. Photos in post 1 and 105 show the rectifier location at the RH end of the board and you can make out the rectifier connections. The 16 volts that you have must be at the input to the rectifier - the heater and HT of course come direct from the transformer. Last edited by Borderer; 3rd Jan 2023 at 8:22 pm.

3rd Jan 2023, 9:03 pm	#122
ben Dekatron Join Date: Aug 2006 Location: Madrid, Spain / Wirral, UK Posts: 7,498	Re: Fidelity transistorised Playmaster - reverse engineering? Thanks. Replaced missing rectifier bridge, 1000uF smoother (+ve gnd), replaced missing 1000uF cap on output stage. Replaced 1x 25uF/25v cap which had leaked and had leg hanging off. Now there is hum and a slight crackle from speaker if volume adjusted. If REC selected green segment in magic eye lights up, but just as one dull blur. So, some progress but still not operational. Will keep at it. __________________ Regards, Ben.

3rd Jan 2023, 9:41 pm	#125
Chris55000 Nonode Join Date: Aug 2007 Location: Walsall Wood, Aldridge, Walsall, UK. Posts: 2,868	Re: Fidelity transistorised Playmaster - reverse engineering? . . .Oh dear, I'll have to get those Playmaster remains out from under my bed and get on with some more drawing–out me thinks – (it got put on one side because of holidays, eye–surgery, repair work for another Member, now complete), and the panel I got being only part–complete, hence me having to puzzle some of it out still! Chris Williams __________________ It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed!

28th Nov 2023, 11:15 pm	#126
ben Dekatron Join Date: Aug 2006 Location: Madrid, Spain / Wirral, UK Posts: 7,498	Re: Fidelity transistorised Playmaster - reverse engineering? I recently looked at my moribund unit again. A dodgy design to begin with and an example which had missing parts and had been got at -a glutton for punishment am I! One of the output pair was s/c, I replaced the AC128 and AC176 with an AC187 /AC188 pair which I had to hand, now there's quite a strong output but the signal is of terrible quality, very distorted/fuzzy and a bit of buzz. The winding for track 1 of the R/P head is o/c, so am awaiting a suitable replacement. Erase does not work. For all I know the erase head may be open too! The odd display on the EM87 was due to a green (signal?) and a yellow wire having detached themselves from the pcb. Now when Rec is selected the display is a bit jittery, but not blurred. I will do some more tests on the resistors and erase head if/when I get a new R/P head. __________________ Regards, Ben.