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Analogue Electronic Repairs

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Analogue Electronic Repairs

Repair of all things electronic, analogue and digital. Vintage HiFi and valve equipment a speciality.

03/05/2026

It's been a very busy start to the year with a lot of uninteresting business as usual type stuff. I thought this David and Goliath fault on a vintage PSU was worth posting. This is what a professional 20A linear PSU looks like, an uncomfortable one person lift and not much better for two people over relativity short distances! The unit presented with no regulation, output over Voltage for selected coarse range at full smoothed rectified Voltage. Removing the plug in PCB containing the regulator circuit resulted in no output, eliminating the pass transistors. A quick check in circuit showed resistive (not short circuit) junctions B-E B-C on VT1, out of circuit checks confirmed this. Both VT1 and VT2 replaced with BC558. So the mighty Farnell B30/20 was defeated by the lowly 2N3702, but not for long! The specifications for this unit are quit impressive, 70's design, built early 80's still going strong.

31/12/2025

Taking some time during the holidays to repair some 8" speakers, practice makes perfect...

25/12/2025

Providing some hope at Christmas. Recently my Tektronix 2430A developed a fault on channel 1 where it would appear to go from normal (pic 1) to maximum gain when 20MHz bandwidth selected, this occurred within 10 mins of initial power up. Setting X to 5ns/div would resolve an approximation to a sine wave, 2nd pic. My thoughts immediately went to CCD issues - sad face. Reading through the service manual pointed to issues with the peak detect, U 440 (ch1). So as a check ch1 and ch 2 (U340) units were swapped along with cleaning (IPA and cotton buds) of the contacts and chip pads. The problem has not reoccurred since reassembly, running good for 3+ hours (pic 3). Fingers crossed!

09/11/2025

Tone don't work...

02/11/2025

So a Guy (no pun intended) that I do a lot of repairs for had an unexpected 'smoke on the water' moment while setting up for a gig recently. These RIFA capacitors carry one cast iron guarantee - they will fail. There are much better alternatives that can be fitted before the inevitable bang happens. Nord stage. The Howling Clowns Guy's Guitar Repair

27/10/2025

New toy day (Polar B2000A). So that's 1 dead ROM and multiple RAM chips identified in no time. Now to find some spares at a reasonable price. Commodore 32k PET .

26/10/2025

No it's not the power button. Yamaha P-45B keyboard. Power will not latch, but works OK if power button held down. 57 screws later (praise the gods of low torque impact drivers!) the power switching board is exposed. Momentary action power switch takes /PSWI low (micro input) via D104 also via D103 takes FT101 g low, turning on 12V supply. Micro responds to /PSWI with PSWO high latching FT101 on - or should do. Looking at PSWO, 3V3 supplied to R105 but instead of expected ~0.6V at TR101 base there was ~1.2V. Immediately suspect TR101, replaced, all working as should. TR101 b-e junction on Polar T1000 analogue signal analyser (video) and curve tracer. Both show abnormalities. 57 screws replaced, plus PCB mounting screws and it's on it's way back home.

05/10/2025

Moog mother-32, dead. Despite the lack of available service information the well laid out PCB, with labelled test points made fault finding relatively easy. R51 2R2, forming a filter network with C28, was found to be high - ~45Ohms. Resulting in loss of 12V to subsequent 10V and 5V rails. I'm seeing quite a lot of SMD resistors failing this way despite being operated well within their rated power dissipation. I can't prove definitely but I suspect the bond between resistive element and end cap is to blame. BTW, the number of fixings to remove for access on these is insane! 🤣

29/08/2025

Because hFE is not a single value.
Because low Voltage testing does not always find the driver transistors that once again take out the newly installed outputs.
Because capacitor leakage current can be measured 150VDC - nA.
Because so much more.....
This vintage unit has prevented more headaches than paracetamol!

28/08/2025

New (to me) scope day. I have been looking for this combination for quite a while, not so common in the UK. High sensitivity differential input plug-ins with low & high frequency cut off filters for noise reduction. Ideal for low level audio work.

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