Hello all! I recently bought a Quad 44 that came with a faulty FM4. It couldn't pickup stations and was drifting. After opening it up I saw a number of faults, leaking capacitors and a blown AFC capacitor. The battery though had been replaced and had not leaked on the board, which was nice. I scraped away the paint around the areas of the leaking electrolyte until the copper was clean, put some flux and solder on and cleaned up with a solder braid. No traces seems to have received any serious damage. After that I performed a full recap and replaced some resistors that had taken some damage.
It's now working, stations are precisely at the frequency they should be and reception is good. The bandwidth ends at 104.3 which seems kinda low though. The problem I'm faced with is that at turn on number 3 on the pre set is on, and the rest of the pre set's, as well as the "Tune" button, is not selectable. So it's stuck at number 3. I've measured the 1n823 diode and there's 6.21volts across it. I've also replaced all 1n4148 diodes. I've also replaced the LED diode which was broken. The rail voltage sits at exactly 12volts. Could this be a fault with the TMS1000 chip? Anyone else had this problem and know's where to look next?
It's now working, stations are precisely at the frequency they should be and reception is good. The bandwidth ends at 104.3 which seems kinda low though. The problem I'm faced with is that at turn on number 3 on the pre set is on, and the rest of the pre set's, as well as the "Tune" button, is not selectable. So it's stuck at number 3. I've measured the 1n823 diode and there's 6.21volts across it. I've also replaced all 1n4148 diodes. I've also replaced the LED diode which was broken. The rail voltage sits at exactly 12volts. Could this be a fault with the TMS1000 chip? Anyone else had this problem and know's where to look next?
There is an upgrade for the FM4 CPU that makes it more stable and also doubles the number of presets by storing two on each button. The new CPU is available from Dada Electronics. That should sort your problem.
If you still can't get the required tuning range, then check the tuning reference zener. If the reference voltage is 6.2v the range is 21.5MHz, so the tuner can be set by adjusting L6 to cover 87.5 to 109 MHz as per the Quad specification. At 6.0 volts the range is 20.8Mhz, so the tuner could be set to cover from 87.6 to 108.4, which still more than adequately covers the FM band for most counties. If I recall correctly there's a mod to the voltage regulator used for tuning that makes it more stable with temperature variation; check with Dada.
If you still can't get the required tuning range, then check the tuning reference zener. If the reference voltage is 6.2v the range is 21.5MHz, so the tuner can be set by adjusting L6 to cover 87.5 to 109 MHz as per the Quad specification. At 6.0 volts the range is 20.8Mhz, so the tuner could be set to cover from 87.6 to 108.4, which still more than adequately covers the FM band for most counties. If I recall correctly there's a mod to the voltage regulator used for tuning that makes it more stable with temperature variation; check with Dada.
Thanks John! Have emailed Quad about it now, it's currently sold out at Dada. I actually have 2 FM4's, both that have been faulty and been repaired by me. I tried the IC1 from the working unit in this faulty one, and now it works flawlessly! Tuning range is all good. Nice to know that it was the chip that was at fault. Happy holidays!
You could try Dada Australia http://dadaelectronics.com.au/drupal/forsale Esmond may have stock. I believe he is a member here also.
Yes I do have stock, and I also have a couple of salvaged working original IC1s as well. Thanks for the mention.
EJP
EJP
Hi ejp, I am trying to source an original processor (IC1) for my Quad FM4. I must have fried it when, cleaning up battery spillage, I inadvertently soldered R21 (470 ohms) to pin1 (12V to IC1) instead of R19 (470K ohms). I read your interesting post dated 20-12-24 where you mentioned you had a couple of original IC1's. I know it is a long shot, but if you do still have one please let me know.
I live Dorset UK.
Many thanks, Kanchenjunga
I live Dorset UK.
Many thanks, Kanchenjunga
